Robert E. Horton Medal

Information on the Horton Medal

The Robert E. Horton Medal is given annually to one honoree in recognition of outstanding contributions to hydrology. Established in 1974, the Horton Medal is named in honor of Robert E. Horton, who made significant contributions to the study of the hydrologic cycle. Medal recipients typically work in one of the following disciplines: biogeosciences, cryosphere, Earth and planetary surface processes, hydrology, nonlinear geophysics and near surface geophysics.

Woman Biological Researcher Taking a Water Sample from a stream.

Award Benefits

AGU is proud to recognize our honorees. Recipients of the Robert Horton Medal will receive an engraved medal, as well as the following benefits with the honor:

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    Awardee will be made an AGU Fellow (if the honoree has been an AGU member for three consecutive years and is not already a Fellow)
  • 2
    Recognition in Eos
  • 3
    Recognition at the AGU Fall Meeting during the award presentation year
  • 4
    Four complimentary hotel nights at the AGU Fall Meeting during the award presentation year
  • 5
    Two complimentary tickets to the Honors Banquet at the AGU Fall Meeting during the award presentation year


To better understand eligibility for nominators, supporters and committee members, review AGU’s Honors Conflict of Interest Policy.

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    Nominees: The nominee should be a senior scientist, but is not required to be an active AGU member. They should be in compliance with the Conflict of Interest Policy.

  • 2

    Nominators: Nominators must be active AGU members and in compliance with the Conflict of Interest Policy. Duplicate nominations for the same individual will not be accepted. However, one co-nominator is permitted (but not required) per nomination.

  • 3

    Supporters: Individuals who write letters of support for the nominee are not required to be active AGU members but must be in compliance with the Conflict of Interest Policy.

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Nomination package

Your nomination package must contain all of the following files, which should be no more than two pages in length per document. For detailed information on the requirements, review the Union Awards, Medals and Prizes Frequently Asked Questions.

  • A nomination letter with one-sentence citation (150 characters or less). Letterhead stationery is preferred. Nominator’s name, title, institution, and contact information are required. The citation should appear at either the beginning or end of the nomination letter.
  • A curriculum vitae for the nominee. Include the candidate’s name, address and email, history of employment, degrees, research experience, honors, memberships, and service to the community through committee work, advisory boards, etc.
  • A selected bibliography stating the total number, the types of publications and the number published by AGU.
  • Three letters of support not including the nomination letter. Letterhead is preferred. Supporter’s name, title, institution, and contact information are required.

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Horton medalists are evaluated by the following four criteria: scientific excellence, scientific impact, broader impact, and reputation and leadership. Specific criteria include:

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    The scientific excellence of the candidate’s body of work over a sustained period of time (this medal is for lifetime achievement) and the publications that have resulted, as well as the insights gained (including contributions across the earth and space sciences).
  • 2
    How the candidate’s work has made a significant impact on his/her field overall, and/or to its growth, through influencing current and future research—articulate these contributions and their importance in a way that can be understood by peers and those outside their research field
  • 3
    Who has benefitted from the work, and the candidate’s recognitions and notable service to his/her field, aligning these with AGU’s mission and vision.
  • 4
    The nominee’s international reputation in his/her field.
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Past recipients

Martinus Van Genuchten


S. Majid Hassanizadeh was awarded the 2019 Robert E. Horton Medal at AGU’s Fall Meeting 2019 Honors Ceremony, held on 11 December 2019 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



Majid Hassanizadeh has made seminal contributions to hydrological sciences through pioneering and highly impactful research in the formulation of fundamental theories for flow and transport in porous media and is most deserving of receiving this honor. With this recognition, he joins a group of world leaders and pioneers who changed the field of hydrology with lasting scientific and broad societal impacts.

Dr. Hassanizadeh, in his almost 40-year-long career, has made significant contributions to the fundamentals of porous media processes that have led to a new paradigm in modeling critical porous media–related processes in the hydrologic cycle, geologic media, and industrial systems. Early in his career, in collaboration with William Gray, he developed a rigorous and unified approach based on averaging and the principles of physics and thermodynamics, referred to as the “hybrid mixture theory” and “averaged thermodynamic approach” for basic porous media process formulation. The approach has been employed to derive new and advanced theories for non-Fickian and high-concentration dispersion and nonequilibrium capillarity and to extend Darcy’s law for two-phase flow. This work identified a new macroscopic state variable for two-phase flow, called fluid-fluid specific interfacial area, which explicitly accounts for the physics of phase interfaces and allows physically based modeling of capillary effects. He also derived a theory that allows computing the distribution of fluid saturation fields as well as the spatial and temporal variations of the average interfacial area. His pioneering work has contributed some of the few new additions to theories of two-phase flow that have existed for decades. These formulations have also resulted in a vast body of research by mathematicians, experimentalists, and numerical modelers. The power of the averaged thermodynamic approach was further demonstrated through the introduction of the new concept of the “representative elementary watershed” that allows for physically based modeling of hillslope processes and channel networks.

Majid’s services to the field as an editor and associate editor of leading hydrology journals, organizer of major conferences, and mentor of young researchers are unparalleled. As a scientist with a vision and a sense of service to the community, he set up the International Society for Porous Media (InterPore), dedicated to establishing porous media science as a new discipline. Majid’s leading role in porous media research has earned him numerous awards and recognitions, including the Royal Medal of Honor of the Netherlands (Knight of the Order of the Netherlands Lion), which is one of the highest civilian awards.

—Tissa Illangasekare, Colorado School of Mines, Golden


I am extremely honored to receive the Horton Medal. After a long journey in research and education, it is the most rewarding feeling to know that many have found value in my work. I am grateful to my nominator, Tissa Illangasekare, and supporters Mike Celia, Rien van Genuchten, and Günter Blöschl, who have followed my work closely and, most importantly, have offered their sustained support and valuable friendship.

When I was a child in Iran, I was always fascinated by natural springs, where the water seemed to appear from nowhere. Also, qanats that bring groundwater to the land surface by gravity were a mystery to me. Reading through Persian literature, one notices the precious role groundwater played in the rich Iranian history and civilization. No wonder, in pursuing advanced studies, I chose groundwater as my focus. My Ph.D. research was in obtaining generalized laws of fluid flow in porous media. Under the guidance of William Gray, I was able to develop a unified approach based on combining volume averaging and rational thermodynamics for deriving equations governing fluids flow and solute transport in porous media. This work led to a truly generalized Darcy’s law for two-phase flow and a related nonequilibrium capillarity formulation. According to standard two-phase flow theory, capillary pressure is equal to the difference in individual fluid pressures, and saturation is the only state variable needed to describe the flow behavior. My work allowed me to question these long-standing assumptions. In particular, it showed that we need to include information about how fluids are distributed in the pores at a given saturation, and it naturally led to the introduction of fluid-fluid interfaces as a new state variable for fully characterizing two-phase flow. There is now overwhelming evidence that at any given saturation, fluids within pores can be distributed in many different configurations. The developed interfacial area model of two-phase flow and the nonequilibrium capillarity model have allowed us to describe complex processes in industrial porous media, such as diapers, fuel cells, and paper.

I am very aware that lifetime achievements, recognized by the Horton Medal, are not achieved by one individual. I have been blessed to have had the best people to help me realize this achievement. I am enormously grateful to my family, students, collaborators, and colleagues for their countless contributions over the years, helping me to get here. I proudly share this recognition with them while dedicating the medal itself to all Iranian scientists who, under very trying conditions, continue exploring new knowledge in many creative ways.

—S. Majid Hassanizadeh, Department of Earth Sciences, Utrecht University, Netherlands

Dennis P. Lettenmaier was awarded the 2018 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 12 December 2018 in Washington, D. C. The medal is for “outstanding contributions to hydrology.”



Over the past 3 decades, Dr. Lettenmaier has grown into the foremost pioneer in hydrologic land surface modeling. His key overall contribution in this evolution has been to take the lead in the macroscale parameterization of land surface variability, as it controls runoff production, integrated with a full land surface energy balance, including the effects of vegetation. With newly available global data sets, this combination of energetics appropriate for different scales has represented the critical step toward the study of continental and global hydrology, a challenge made by Eagleson in the 1980s to the hydrologic community. The foundational references by him and his collaborators have been widely used by scientists from as many as 54 different countries.

In parallel, Dr. Lettenmaier led major breakthroughs regarding the effects of climate and climate change on the hydrologic cycle. This work indicated how climate change issues can result in vastly different responses in the timing and amount of surface runoff, allowing the development of strategies for threatened arid-region basins. In systematic analyses of climate change in cold regions, he and his team developed a quantitative basis for estimating the fraction of snowmelt in the annual runoff of major river basins, and they explored the relative controls of temperature and precipitation changes on mountainous snow packs, causality of flood frequency changes, snowpack-associated runoff, evaporation, and, most recently, novel algorithms for frozen soils and permafrost representations and for snow interception and blowing snow.

Beside these two main lines of enquiry, Dr. Lettenmaier has made successful explorations of other areas as well. For instance, regarding the hydrologic aspects of the Anthropocene, he investigated and evaluated the relative impacts of climate change and land cover changes in coastal lowlands. In a major improvement in drought assessment, with his associates he put forth a severity-area-duration method, allowing unbiased comparison of envelope droughts over large continental areas.

These scientific contributions are widely acknowledged, and Dr. Lettenmaier has already been recognized with several prestigious awards. In addition, he has distinguished himself by his unselfish cooperation and leadership initiatives, as borne out by the numerous committee and editorial responsibilities he has assumed over the years. The Horton Medal is awarded in recognition for “outstanding contributions to hydrology.” Unquestionably, Dr. Lettenmaier is a perfect embodiment of this ideal: His superior contributions through his intense dedication in scholarship and service place him among the very best in our hydrologic community.

—Wilfried H. Brutsaert, Cornell University, Ithaca, N.Y.


I want to thank my nominator, Wilf Brutsaert, for his kind words, and Dan Cayan, Randy Koster, and Soroosh Sorooshian, who wrote in support of Wilf’s nomination. I also thank the many students, postdocs, and staff who’ve worked with me over the years. This award is really about them.

I was lucky that my career coincided with a major transformation in hydrology and that it came about at an opportune time for me. In the mid-1980s, I was asked to participate in Environmental Protection Agency’s (EPA) report to Congress on the effects of climate change on the United States. EPA wanted a study of climate change effects on California’s water resources. I thought we could investigate a single reservoir to which we would perturb inputs on the basis of assumed changes in precipitation and evaporative demand. The response was “not good enough, we need you to do all of California.” I really had no idea how, but with postdoc Thian Yew Gan doing the hydrologic modeling and Dan Sheer the reservoir operations, we glommed something together. The exercise made clear to me that we simply didn’t have the tools to do large-scale hydrologic prediction at that point. Shortly thereafter, discussions with Eric Wood led to conceptualization of the VIC model, followed shortly thereafter by Xu Liang’s dissertation work that developed the first version of the model. That in turn led to further development work by many students and postdocs at the University of Washington and Princeton University. It also led to a host of studies on topics we (or at least I) hadn’t begun to think of in those early days—drought work (Kostas Andreadis and Kingtse Mo), data assimilation (Kostas Andreadis), and Arctic hydrologic processes and change (Laura Bowling, Fengge Su, and Jenny Adam), among just a few. In more recent years, we’ve turned our attention from “what will happen if” questions to “what has and is happening” in the spirit of what Rich Vogel has termed hydromorphology. In that vein, I think in particular of Phil Mote’s declining mountain snowpack papers and current student Mu Xiao’s recent Water Resources Research paper on causes of declining Colorado River streamflows. All told, it’s been a great ride.

In closing, I want to thank AGU, which has been my professional home for well over 40 years. I think especially of AGU’s motto “unselfish cooperation in research,” which typifies the many collaborators I’ve worked with over the years; it’s their shoulders on which I stand. Thank you to all.

—Dennis P. Lettenmaier, University of California, Los Angeles

Eric F. Wood was awarded the 2017 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 13 December 2017 in New Orleans, La. The medal is for “outstanding contributions to hydrology.”



The awarding of the Robert E. Horton Medal to Eric F. Wood recognizes him for major advances he has made toward ­process-­based representation of global hydrology through developing hyperresolution models and enhancing them dynamically with remotely sensed observations using novel methods of data assimilation.

Eric was a pioneer in fundamental research on scaling and similarity of catchment hydrologic responses. He introduced the “representative elementary area” concept that showed that catchment response could be represented in terms of “building blocks” of some minimum size. This breakthrough launched him into the era of spatially distributed hydrologic modeling. Eric was the first to develop a distributed modeling framework that accounted for the effects of topography and land ­surface–­atmosphere interactions involving coupled ­water–­energy dynamics. Many of the distributed modeling concepts Eric pioneered found their way into the Variable Infiltration Capacity (VIC) macroscale hydrology model, which is the default land surface parameterization scheme in many global circulation models used in global change science.

Building on the success of distributed models at river basin scales, Eric Wood and his colleagues extended the modeling all the way to the globe and used the models to make predictions of river flows, floods, and droughts, discovering interesting regional and global patterns. At the continental and global scales, Eric made major contributions to increasing the predictability of streamflow by taking advantage of both soil moisture and precipitation data from satellites. He developed new conceptualizations of radiative transfer that allowed ingestion of radiation data directly into hydrologic models. Eric’s research also showed that knowledge of initial soil moisture provides the main source of forecasting skill and that the potential for improved forecasts was limited by the accuracy of precipitation estimates. Eric’s frameworks for improving predictability have been adopted by major weather forecasting centers around the world to routinely assimilate satellite estimates of land surface conditions into numerical weather prediction models. This enhanced forecast methodology has led to significantly improved drought forecasts.

Finally, through his leadership within global programs such as the World Climate Research Programme and the Global Water and Energy Experiment and his involvement with national organizations such as NASA and the National Oceanic and Atmospheric Administration (NOAA), Eric has steered global water research along his vision of global, distributed hydrology. The promise of global hydrology, deemed impossible only a few years ago, has now been realized through the efforts of Eric Wood, and he is therefore a deserving recipient of the Robert E. Horton Medal.

—Günter Blöschl, Vienna University of Technology, Vienna, Austria


I’m honored that AGU selected me to receive the Robert E. Horton Medal, and I thank Professor Günter Blöschl for the kind citation that provides a summary of my contributions. Over the past 40 years many people contributed to my research—over 30 Ph.D. students, 30 postdocs and research staff, and many collaborators. While space limitations preclude listing all of them and the ways they contributed, I would like to provide a perspective on the evolution of the research summarized in the citation. In the early 1980s, Keith Beven encouraged me to think about ­process-­based hydrologic processes that led to my “Representative Elementary Area” concept. Understanding the impact of landscape variability on water and energy fluxes has been an unresolved research problem, but the work of M. Sivapalan, W. Crow, and C. ­Peters-­Lidard indicated that ignoring such variability leads to biased surface fluxes. Including spatial variability in land surface models led to my ­30-year collaboration with Dennis Lettenmaier in the development of the Variable Infiltration Capacity model, which started with Xu Liang’s Ph.D. dissertation in the early 1990s at the University of Washington. Twenty years later, I proposed the development of hyperresolution land surface modeling (LSM)—30 to 100 meters at continental scales—to capture this variability, which led to the development by my student Nathaniel Chaney of HydroBlocks, which we’ve run at 30 meters across the contiguous United States. In the mid-1990s a strategy was developed for using VIC and remote sensing from small-scale modeling (focusing on processes) to ­continental- to global-scale modeling (focusing on the global water cycle). With Dennis Lettenmaier and his group, we developed the first ­continental-­scale, long-term forcing data set for LSM as part of the North American Land Data Assimilation System (NLDAS), which was used by Justin Sheffield to develop a ­VIC-­based objective drought index and by Ming Pan to develop assimilation systems with remote sensing data. Within the NLDAS project we also used NOAA’s Climate Forecast System seasonal forecasting model to develop seasonal hydrological forecasting and, recently, a multimodel forecast system with my postdoc Niko Wanders. The experience over the United States allowed us to expand to a global domain, where we now run historical and ­real-­time flood and drought monitors as a climate service to help users improve their decisions. I see my Robert Horton Medal as a medal shared with all of my students, research staff, and collaborators who contributed to the work and with the NASA and NOAA program managers who funded my research. I gratefully thank them all.

—Eric F. Wood, Princeton University, Princeton, N.J.

Thomas Dunne was awarded the 2016 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 14 December 2016 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



This is an award that is long overdue. Tom Dunne has been a major influence in hydrology and geomorphology for the past 40 years in a variety of environments, from Vermont to East Africa, the Andes, and the Amazon. Tom’s methodology has been instructive regardless of the domain of his research. During a period when there has been a tendency for researchers to concentrate either on experiments or on computer models, he has always, like Robert Horton, aimed to transfer the knowledge obtained from careful field experiments to the appropriate representation of processes in models. Tom has done this in an exemplary way: runoff generation mechanisms (from hillslopes to the entire Amazon); channel networks (landscape evolution and river habitat); weathering, hillslope erosion, sediment routing, and sediment budgets; river mechanics, meandering, and floodplain depositional processes; and watershed management and river restoration. He has done so at scales from small plots to the Amazon. At times his methods have been unorthodox, such as his approach to simulating the effects of cattle on infiltration rates in East Africa (which makes for a highly entertaining seminar that inspires students).

Tom is a true research scientist, but that has not meant that he has neglected the application of the science to practical problems—that is essentially what his book with Luna Leopold, Water in Environmental Planning, is all about. He has also been prepared to devote time to the wider interests of the hydrological and geomorphological communities, serving on numerous national and international committees, including working for the United Nations.

All of the supporting letters refer to Tom’s inspiring influence on his students and younger colleagues. In his case, it can really be said that he has nurtured them through his intellectual curiosity, by his active contribution to their fieldwork, and via the weekly paper discussion (or dissection) sessions at his home. Many of those students have, of course, gone on to be outstanding hydrologists, geomorphologists, and ecohydrologists in their own right.

Tom’s name is already linked to that of Horton through the descriptions of Horton and Dunne overland flow mechanisms in hydrological textbooks. As Bill Dietrich expressed in his supporting letter, “He took up the charge of Horton’s ‘hydrophysical’ approach and contributed many fundamental insights about surface processes and landscapes. Our understanding of hydrology and geomorphology has been greatly advanced by both his scholarly publications and his intellectual leadership.”

—Keith Bevin, Lancaster University, Lancaster, U.K.


Thank you to Keith Beven and the other supporters of this nomination for providing me with such an honor, and to the audience for letting me enjoy it with you. The heartwarming aspect of the award is that it reminds me of the influences of the communities and institutions in which I have been fortunate to participate. The geography departments at Cambridge and Johns Hopkins impressed on me the importance of constructing theory based on field investigations (working on what Keith frequently emphasizes are our epistemic uncertainties about how landscapes function), and of spending at least a portion of one’s research efforts on topics of societal value. Nairobi and McGill Universities exposed me to the subarctic and tropics, expanding my appreciation of the environmental range of Earth. And in the multidepartmental communities at the Universities of Washington and of California, Santa Barbara colleagues strengthened my geophysical education and expanded the geographical range and time depth of my studies and also my interest in hydrologic and geomorphic contributions to environmental conservation and restoration from the Pacific Northwest to the Amazon Basin. I am mindful that it was possible to learn new things in all the roles I had in these institutions from undergraduate to aging professor. I learned that diversity of scientific approaches and of geographical exposure is valuable and enriching.

But this is also a night to reflect on Robert Horton. He has guided me since my undergraduate days when I was taught that his hydrophysical approach was the key to understanding the fluid mechanical processes driving the formation and hydrological functioning of landscapes. I had to be informed later of the roles that Earth plays in providing the material properties, boundary conditions, and time frames in which those landforms and those functions evolve. But Horton has broader lessons for all of us. He distilled his working engineer’s experience as an observer of nature and his multi­lingual reading into foundational studies across the processes and scales of the hydrologic cycle. In the 1930s, he published a scientific agenda for hydrology and was a ­­­co-­founder of the Hydrology section of AGU in the face of considerable early skepticism about whether hydrology was truly a scientific field. For that, we should be particularly grateful to Robert Horton for providing us with this community and with an opportunity to ask continually whether our own work supports his optimistic vision of what we might accomplish.

—Thomas Dunne, Bren School of Environmental Science and Management, University of California, Santa Barbara

Günter Blöschl was awarded the 2015 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2015 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



Günter Blöschl has been not only a phenomenal researcher, educator, and synthesist but also a visionary leader in catchment hydrology.

Günter’s research has spearheaded a whole-system view that envisions observable spatial hydrologic patterns as manifestations of internal dynamics. Günter’s early work on snow patterns unraveled how patterns of snow albedo, melt, and redistribution are controlled by topography. He devised novel methods to infer the organization of water flow paths from measured soil moisture patterns. He systematically analyzed spatial flood processes to discover regional patterns of rain on snow and flash floods, each having a distinct spatial scaling behavior. He introduced new frameworks for diagnosing flood regime changes across Europe using regional process indicators, permitting attribution of anthropogenic effects. Within the field of sociohydrology he cofounded, he brought out emergent long-term dynamics resulting from two-way feedbacks between humans and floods.

Günter is a true visionary and an innovative thinker, and the many concepts he has introduced have made a huge impact. His scale concepts are used widely across several fields, beyond hydrology. The patterns approach he pioneered has been influential in the way hydrologists look at patterns and processes through the prism of scale. Günter is a synthesizer. Through a synthesis across processes, places, and scales (as part of Predictions in Ungauged Basins) he linked the process representations of low flows, floods, and runoff hydrographs through the concept of water balance, helping to unify the entire field of catchment hydrology.

Günter’s quest for bridging theory and practice has resulted in the adoption of his concept of “flood frequency hydrology,” which enriches statistical approaches with process understanding, by the official flood estimation guidelines in several European countries. The ensemble flood warning system he developed is now used operationally in the Danube River. In these ways, Günter has made a huge impact on both the scientific community and society as a whole. There is no greater evidence of his stature as a geoscientist than his service as president of the European Geosciences Union and his recent election as president of the International Association of Hydrological Sciences.

Günter Blöschl’s innovations grounded in observations, deduction, and theory bear remarkable similarity to the thinking espoused by Robert Horton himself. His visionary and unselfish contributions to the advancement of the field therefore make him a most worthy recipient of the Horton Medal.

—Upmanu Lall, Columbia University, New York, N.Y.


I am delighted to receive this medal and humbled to join the roll of past recipients, including such luminaries as Walter Langbein, Charles Theis, and Mikhail Budyko. I thank Manu Lall for leading the nomination and for his generous citation.

Manu highlighted my work linking patterns to processes. I have always been fascinated by patterns of flowing water and how they come about. One of my favorite pastimes as a child was to sit and watch the flow of water and, where there was an opportunity, to build little dams in mountain creeks or at the beach to divert the water and shape its flow. This may well be the reason why, later in my career, the deductive approach to learning from patterns struck a chord with me. Quoting Sherlock Holmes, “The case is one where we have been compelled to reason backward from effects to causes.” Perhaps we in hydrology too should give greater emphasis to deductions, as opposed to the usual practice of calibrating preconceived models to data, to parallel Sherlock Holmes’s proverbial successes.

Manu also wrote about my passion for bridging theory and practice. I’ve been fortunate to have had Dieter Gutknecht as a mentor who introduced me to hydrology at the crossroads of science and engineering, which soon became second nature to me. Over the years, there have been numerous unexpected synergies, hardly planned but a confluence of circumstances, such as when flood design issues inspired novel estimation methods or when regional process interpretations helped improve practice. The recent 50th anniversary special issue of Water Resources Research again provided an opportunity to reflect on the perennial problem of theory versus practice. As global water pressures mount, interaction between human and water systems is enjoying a great revival, with renewed focus on feedbacks and coevolutionary processes. This is an exciting prospect that, I hope, will lead to a happy synthesis of two theses often mistakenly considered antitheses.

While I take pride in receiving the Horton Medal, I share it with Rodger Grayson, Andrew Western, Ralf Merz, Duro Paraj-ka, Robert Kirnbauer, Alberto Viglione, Bruno Merz, Jan Szolgay, Siva Sivapalan, Hubert Savenije, Alberto Montanari, and many other colleagues, as well as generations of my students, who have greatly shaped my intellectual development. My final words of thanks go to my wife, Elisabeth, and our wonderful children, Roman, Agnes, and Margit, for their love and support over many years.

—Günter Blöschl, Vienna University of Technology, Vienna, Austria

W. James “Jim” Shuttleworth was awarded the 2014 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 17 December 2014 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



Professor W. James Shuttleworth has brought innovative research, novel scientific thinking, and outstanding leadership to the interface between hydrology and other Earth science disciplines. He has motivated young hydrologists to move beyond established boundaries and brought the hydrologic and atmospheric sciences together to foster the growing field of terrestrial hydrometeorology.

A cornerstone of Jim’s career has been the development of theoretical and experimental methods that underlie the prediction of natural evaporation and are now the foundation for the land-atmosphere models used in numerical weather and climate prediction. He is regarded as the leading international expert on evapotranspiration, and his work led a transformation to physics-based formulations based on the laws of conservation of mass and energy. It is, therefore, no surprise that he was asked to write the chapter on evaporation in the Handbook of Hydrology.

Jim pioneered the modern era of environmental investigations in the Amazon River Basin, where his team developed the capability to measure surface-atmosphere exchanges, ultimately revealing that theories about seasonal variations of evapotranspiration there were wrong. His precedent of combining research with training young scientists is a key aspect of the Large Scale Biosphere-Atmosphere Experiment (LBA).

Jim was arguably the first hydrologist to understand the importance of the hydrology-ecology interface to climate and weather prediction. His papers established a subfield of hydrology devoted to large-scale modeling and prediction. He helped organize and lead large international multidisciplinary research initiatives to improve the representation of surface exchanges in meteorological models and to acquire the data required to test and improve them.

Perhaps most noteworthy, however, is Jim’s leadership in developing terrestrial hydrometeorology as a major discipline of Earth system science, resulting in the world’s first graduate degree program in this subject at the University of Arizona. Characteristic of this leadership, he published the first textbook on the subject, and it is destined to become a classic and basic text for similar academic programs elsewhere.

In summary, Professor Shuttleworth has been an intellectual leader in the field of hydrology for over 40 years and has contributed to broad philosophical perspectives in hydrology, as well as hydrologic understanding and prediction based on careful integration of observations and theory. He has been a prime motivator in vigorous discussions that have been illuminating but never divisive. He is a true gentleman, recognized for his honest commitment to advancing science for the benefit of society, and a consummate example of AGU’s motto “unselfish cooperation in science.”

—Hoshin V. Gupta, University of Arizona, Tucson, Ariz.

—Dennis P. Lettenmaier, University of Washington, Seattle, Washington


I am humbled and honored to receive this year’s AGU Horton Medal and sincerely grateful to my nominators, Hoshin Gupta and Dennis Lettenmaier, and to those who wrote in support.

I am lucky to have worked in hydrological science research during 40 years in which it grew hugely in the range of other environmental sciences with which it interacts and in acknowledgment of its importance to humanity. My career was carried forward by this growth.

I am lucky to have worked in two centers of excellence during periods when each experienced the zenith of their success. First, I worked at the UK Institute of Hydrology (IH) when that institution, under Jim McCulloch, was the flag bearer of officer innovation in process studies of surface hydrology. At IH I discovered my passion for understanding natural evaporation and worked with colleagues, including John Gash, Colin Lloyd, Dave McNeil, Chris Moore, Han Dolman, and Howard Oliver, to establish routine application of the eddy correlation method to measure surface exchanges. It is also where, working with Luis Molion, Carlos Nobre, and many, many Brazilian colleagues, we ventured into the then novel hydrometeorological quantification of Amazonian rainforest and where we joined the battle for large-scale quantification of surface-atmosphere exchanges, working with international colleagues, including Jean-Claude Andre, Hans Bolle, Piers Sellers, and Pavel Kabat.

I am lucky because I was next recruited by Soroosh Sorooshian to join the Department of Hydrology and Water Resources (HWR) at the University of Arizona, a unique and massively productive center for hydrological science research. There I work in a stimulating environment with colleagues, including Hoshin Gupta, Tom Maddock, Juan Valdes, Paul Brooks, Shlomo Neuman, and Marek Zreda, to extend studies of surface exchanges with greater emphasis on using remote sensing and on research implemented through talented graduate students, including Paul Houser, Altaf Arain, Russ Scott, Dave Gochis, Omar Sen, Ismail Yucel, and Chawn Harlow, to name just a few. It is where I have been most active in science management, working in National Research Council committees and the International Geosphere-Biosphere Programme, Global Energy and Water Cycle Experiment, and Climate Variability and Predictability programs, and where my interest in using hydrological research to aid policy arose, fostered via the International Association of Hydrological Sciences’ Hydrology for the Environment, Life and Policy (HELP) program and as director of the Semi-Arid Hydrology and Riparian Areas Science and Technology Center.

But I am lucky most because I married my wife, Hazel, who, throughout 50 years of marriage, has been my consistent supporter and who has given me my children, Craig, Matthew, Nicholas, Jonathan, and Amy, and 11 grandchildren and three great-grandchildren!

—W. James “Jim” Shuttleworth, University of Arizona, Tucson, Ariz.

Soroosh Sorooshian was awarded the 2013 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 11 December 2013 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



I am proud to introduce Soroosh Soroosh­ian, distinguished professor of civil and environmental engineering and Earth system science at the University of California, Irvine, as the 2013 Horton medalist. Soroosh is an exemplary scholar, who through collaborations with Hoshin Gupta and numerous other talented students and researchers, has made many landmark contributions to hydrology. I will highlight what I consider to be his principal contributions. In the early 1980s, Soroosh was among the first to provide a better statistical underpinning of the rainfall-runoff model calibration problem. This work is still a main reference for hydrologic parameter estimation. Later that decade, Soroosh was the first to explain why local search methods were unable to locate the “best” hydrologic parameter values. This led to the SCE-UA algorithm. The profession suddenly had a consistent way to calibrate watershed models.

In the 1990s, Soroosh and his students introduced artificial neural networks to model the rainfall-runoff transformation. This work reenergized interest in black box models. Later, Soroosh’s group presented a multicriteria approach to model calibration that opened up new frontiers and inspired many of us to better recognize the role of model error. Soroosh then embarked upon a journey to use remote sensing data for precipitation estimation. This led to PERSIANN, used worldwide to predict rainfall amounts at different spatial and temporal scales.

In the 2000s, Soroosh and his students introduced particle-filtering and model-averaging approaches to better characterize modeling errors. This work is at the center of the current debate on uncertainty quantification and has revived the use of data assimilation approaches.

At the same time, Soroosh engaged in sustainability studies to improve water resources management by initiating the Sustainability of Semi-arid Hydrology and Riparian Areas (SAHRA), a National Science Foundation Science and Technology Center. Especially noteworthy are his contributions to understanding the role of climate and soils in regional- and global-scale hydrology, inferring snowpack depths and riparian vegetation from remote sensing data, and understanding the relationship between seasonal streamflow variations and snowpack in the western United States.

Most recently, Soroosh started working on the effects of irrigation on local/regional weather and climate. Further, he has worked tirelessly in the service of the community, as chair of the Science Steering Group of the Global Energy and Water Cycle Experiment (GEWEX), a member of the National Oceanic and Atmospheric Administration Science Advisory Board, and a member of several National Research Council committees. He has also testified to both the U.S. House and Senate committees on water resources issues and has served AGU in numerous roles: editor of Water Resources Research, Hydrology section president, and chair of the Public Affairs Committee.

Soroosh is also an outstanding educator. Many of his former students occupy leading positions in academia, industry, and government. In summary, Soroosh is a skilled diplomat who has propelled hydrology to new synergies and discoveries. His wisdom and vision have inspired many to succeed in their careers. Please join me in congratulating Soroosh Sorooshian as this year’s Horton Medal winner.

—JASPER A. VRUGT, University of California, Irvine


It is a true honor to be named the 2013 Robert E. Horton medalist by AGU. To be considered for such an honor, one must be nominated for consideration. I am grateful to Jasper Vrugt for having led my nomination and to colleagues who wrote supporting letters on my behalf.

My journey to present started in 1967 when I arrived in California from Iran to pursue college education. Cal Poly–San Luis Obispo, where I earned my B.S. degree in mechanical engineering, provided the finest possible hands-on engineer education one could wish for.

My graduate studies at the University of California, Los Angeles (UCLA) in systems and water resources engineering provided me the most unique opportunity to think outside the traditional disciplinary framework and led to my research interests in the parameter estimation of hydrologic models using my optimization knowledge.

I owe much to the three academic institutions (Case Western Reserve University (CWRU), the University of Arizona (UAZ), and the University of California, Irvine (UCI)) that have given me the opportunity to teach and pursue my research interests with access to some of the finest doctoral students one can wish for.

AGU was the first professional society I joined as a member. By far, among all my professional activities AGU has played a key role in my success, with the Horton Medal being the capstone. Serving as the editor of Water Resources Research provided me the opportunity to appreciate the wide range of facets of the hydrologic cycle, leading to some of my research pursuits in hydroclimatology. The presidency of the Hydrology section also provided the most valuable experience with respect to leadership in the functioning of a large professional organization such as AGU.

While the honor has come to me, it is a shared prize with many people who, over the past 40 years, have played a major role in my career. First and foremost is John Dracup, my Ph.D. advisor at UCLA who introduced me to surface hydrology and rainfall runoff modeling; William “Bill” Yeh and Moshe Rubinstein of UCLA also played a major role in my career development. A special thanks goes to Yacov Haimes, who recruited me for my first academic job at CWRU.

During my 20 years at UAZ I benefited from the friendship and wisdom of many colleagues, particularly Ernest Smerdon, Shlomo Neuman, Lucien Duckstein, Tom Maddock, Jim Shuttleworth, Juan Valdes, Roger Bales, and my deceased colleagues Nathan Buras, Don Davis, and Stan Davis.

The contributions of my former graduate students to my success have been indispensable. To name a few, I am indebted to my first doctoral student, Hoshin Gupta. Also, I wish to acknowledge Qingyun Duan, Kuolin Hsu, Xiaogang Gao, David Goodrich, Bisher Imam, and Karen Humes for encouraging me to pursue hydrologic remote sensing.

I would be remiss if I did not acknowledge a few special colleagues, such as Steve Burges, David Dawdy, and John Schaake.

Finally, no success in one’s career can be achieved without the unconditional support of family. My wife of 38 years, Shirin, has done so much that words cannot express my gratitude. Our two sons, Jamshid and Armin, successful in their own respective careers, have been a source of joy and pride for us.

—SOROOSH SOROOSHIAN, University of California, Irvine

Keith Beven was awarded the 2012 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 5 December 2012 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



It is a pleasure to introduce Keith Beven, currently Distinguished Professor at Lancaster University UK and visiting Professor at Uppsala University, Sweden and EPFL, Lausanne, Switzerland, as the recipient of the 2012 Robert Horton Medal. Keith’s contributions to the geophysical aspects of hydrology are unusually rich. Keith is the world’s most cited hydrologist and continues to be the thought leader in the area of rainfall-runoff processes, hydrological modeling, and uncertain estimation techniques. As an experimentalist, Keith has made substantial contributions to soil physics and our understanding of preferential flow. His early work linking preferential flow and kinematic wave approaches forms the foundations of the field. As a modeler, Keith’s TOPMODEL concept (developed with Mike Kirkby) ushered in a new approach to catchment modeling, one driven by terrain information and process-based assumptions of how water is routed to the stream. TOPMODEL components, like the topographic index and the concept of hydrological similarity have influenced many fields outside of hydrology, including geomorphology, ecology, geotechnical engineering, and atmospheric science. Keith has done more than any other hydrologist to show that estimation of uncertainty is an integral part of environmental modeling. The concepts that he has introduced, such as equifinality and uniqueness of place, have helped define current practice. The tools that he has developed, like the Generalized Likelihood Estimation Technique (GLUE), have helped operationalize the regular use of uncertainty techniques. For these contributions, Keith has been an AGU Fellow since 1995 and has been awarded the Dalton Medal from the European Geophysical Union, the Hydrology Section Award, and the IAHS/WMO/UNESCO International Hydrology Award.

Keith has been a keen student of hydrological history, compiling the first IAHS Benchmark Papers in Hydrology volume on Streamflow Generation Processes. In that work, he showed remarkable sense of the evolution of the discipline, reverence for the main contributors to the science, and guidance for the would-be student to find her or his path through the literature. Keith has also been a student of Horton. Keith’s AGU Langbein Lecture in 2004 was titled “Robert Horton and the application of distributed hydrological models.” He, more than any other hydrologist since the late Walter Langbein, has honored the Horton legacy. His hydrological sleuthing revealed many hitherto unpublished contributions to the field by Horton; including new insights into how Horton viewed the infiltration process and groundwater dynamics.

Despite all his accolades and honors he has received, he is a most humble and unselfish giver of time. He collaborates extensively with junior and senior colleagues across the world, and has provided a large and distinguished set of students and coworkers with inspiration and insight. He has twice been awarded the AGU Commendation for Excellence in Refereeing. This speaks volumes for the character of the man and the way he impacts the field unselfishly through his actions.

In short, Keith Beven is an outstanding scientist and person, and a truly worthy and highly appropriate recipient of this year’s medal.

–Jeff McDonnell, University of Saskatchewan, Saskatoon, Saskatchewan, Canada


I am extremely grateful to Jeff McDonnell for having led this nomination and for his very generous citation. I am also, of course, deeply honored by this award, particularly since I have the greatest respect for Robert Horton as perhaps the most important hydrologist of the 20th century. Certainly as far as I know, he is the only hydrologist to have a waterfall named after him, near his home in Voorheesville, New York. That respect was deepened when a few years ago I had the opportunity to look over just a small selection of the 94 boxes of his papers in the National Archives. That showed that he had a much greater appreciation of the complexity of hydrological systems than he is given credit for in current text books. It is that complexity that I have struggled with throughout my career, complexity that is so poorly represented by the available measurement techniques and which makes hydrological prediction so difficult and shot through with epistemic uncertainties, i.e., uncertainties that arise from lack of knowledge rather than random natural variability. The GLUE methodology was mentioned in the citation. It is an on-going research program that tries to deal with uncertainty in nonideal real-world applications when simple statistical assumptions may not be enough. By definition, of course, epistemic uncertainties pose impossible problems to the modeler. If we had adequate knowledge to represent them, they would not be epistemic. But research still thrives on the challenge of impossible problems and I still feel very much like a student trying to understand the problems before I will be satisfied.

No one ever receives an honor like this without being in debt to many people, both teachers and students. In maintaining a student-like approach to research I have been fortunate to have had some rather good mentors, particularly Mike Kirkby, George Hornberger, and Peter Young, all still remarkably active in their own research. I have also worked with people such as Andy Binley, Sarka Blazkova, Jim Freer, Peter Germann, Rob Lamb, Eric Wood, Jeff himself and many others who have contributed hugely to my own development as a student of hydrology and hydrological modeling.

During a lot of my career I have often been somewhat at odds with mainstream hydrological research. Many of my citations have therefore come from papers trying to explain why I have been wrong, or overly subjective, or undermining the science. I will happily admit to often playing the devil’s advocate in trying to persuade others to be more circumspect in modeling these difficult systems. But there is a serious issue at the heart of these debates. As Jay Famiglietti put it so nicely recently, how can we manage water for the benefit of mankind in nonstationary times when we know so little about its various stores, flow pathways, and residence times even in a developed country like the United States? Should these epistemic uncertainties and their effects on model predictions have an effect on our management strategies and decision making? It is all too easy to provide predictions to decision makers these days that are not underpinned by rigorous or adequate science. For example, how should we address the hydrological impacts of climate change on water when predictions of precipitation under current climate are so poor in many parts of the world? How can we be confident about the impact of fracking on water quality in the long term when so much knowledge is lacking? We do know that contamination is one of the greatest factors affecting the available water resource and that once water sources are contaminated they can be hugely difficult and enormously expensive to clean up. In many places it is already too late. How then can we reflect and react to such epistemic uncertainties? The question is urgent in both hydrology and other environmental sciences. It is a question that Robert Horton would be contributing to if he were alive today. I still hope to throw more light on this before I am done.

–Keith Beven, Lancaster University, Uppsala University and EPFL, Lausanne

Murugesu Sivapalan was awarded the 2011 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 7 December 2011 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



It is a pleasure to introduce Murugesu Sivapalan of the University of Illinois at Urbana-Champaign as the recipient of the 2011 Robert Horton Medal.

Sivapalan is a leader in the development of hydrological theory, recognized for publishing influential papers on the fluid mechanics and thermodynamics of water movement at catchment scale, involving hydrology, geomorphology, soil science, and ecology. His pioneering efforts have been extended through sharing his expertise and interdisciplinary perspective as a leader of research groups and pathbreaking workshops. These roles have been acknowledged through his election to fellowship in the Australian Academy of Technological Sciences and Engineering and in AGU, as well as the award of the European Geophysical Society’s Dalton Medal, the International Hydrology Prize of the International Association of Hydrological Sciences, AGU’s 2010 Hydrologic Sciences Award, and the Australian government’s Centenary Medal.

A statistical accounting of Siva’s accomplishments, however, does no justice to the originality of his insights and their impact on the modernization of catchment hydrology.

Siva’s early work on the influence of scale on hydrologic prediction demonstrated that controls on water movement in landscapes have spatial and temporal structures, governed by physical principles and coevolution over various time periods. He proposed that the spatial structures and characteristic time scales of these controls could provide a basis for using general hydrological features in making predictions.

Siva pointed out that predictions of water cycle dynamics face two significant challenges. The first is that environmental change, intensified by anthropogenic influences, implies that historical records cannot be relied on for predictions of future behavior based solely on extrapolation, statistical analysis, and calibration of nominally process based models. Instead, those records, and new types of observations, must be mined for physical insights about how process dynamics and their exogenous controls generate water resources and hazards.

Siva’s second emphasis is the interaction of the hydrologic cycle with other physical, biotic, and social systems. Water is involved in everything from Earth’s mantle through its landscape formation, ­near-­surface and surface water bodies, soil mantle, ecosystems, atmosphere, and even our minds through our desires and group actions. Each of these systems affects the availability of water and, in turn, is affected by it. And each has its own spatial and temporal characteristics of pattern formation and functioning. Understanding the evolution of these patterns and the probability distributions of their properties facilitates predicting behavior of water at catchment scales. Hydrological predictions in nonstationary watersheds must therefore be based on explicit, accurate accounting for changes in structure, drivers, and the resulting dynamics of these interacting systems through formulating physically based models within a statistical framework.

Formulation of hydrologic theory to meet these challenges is what Siva is accomplishing and promulgating. He has articulated the challenge, organized approaches for confronting it, and demonstrated how to make progress. This kind of reach across theory and empiricism and into the future of hydrology as a socially valuable Earth science makes Murugesu Sivapalan a visionary and unselfish contributor to the advancement of the field and a worthy recipient of a medal that reminds us of Robert Horton.

—Thomas Dunne, Bren School of Environmental Science and Management and Department of Earth Science, University of California, Santa Barbara


I am delighted to receive this medal, and even more so to have as citationist Tom Dunne, a hero of mine for over 25 years. At the outset I want to record my sincere thanks to many friends, led by Hubert Savenije, for nominating me for this prestigious medal.

Tom’s citation might have given you the impression that my research was somehow well scripted. Of course, it would be nice if life would be so predictable, even in hindsight. As one who hails from a land once known as Serendib, a little bit of serendipity must have rubbed off on me, so much so that my life’s trajectory has been a series of accidents or inspired choices. Each was a turning point, and yet two constants were the fire instilled in me by my parents and the support of my wife and family. Another was some key people who serendipitously came into my life: teachers who picked me out from the crowd and lifted me up, students who shared their ideas and enthusiasm, a close coterie of friends who offered both honest criticism and unqualified support, and mentors who helped me get over difficult obstacles. Driven by circumstances, I had to pursue my dream in five continents, as a veritable academic nomad, yet I am proud about how much I have gained from each place and the roots I have left behind.

I remember my Ph.D. days as a struggle, with a fear of failure that became the driving force in my later successes. I had framed my Ph.D. thesis using ideas from Jim Dooge and Vit Klemes, yet in the end I felt I did not do justice to them. In a sense, I am still working on my unfinished Ph.D. thesis. My early work was on scale issues in event runoff predictions. I then expanded it to include complete water balance modeling, which propelled me into the Predictions in Ungauged Basins initiative. Fundamental challenges posed by subsurface heterogeneity led me into the “functional” approach to modeling, opening up interdisciplinary collaborations with ecologists and pedologists. Realizing that ­human-­induced change is even more challenging than heterogeneity, predictions under change became a new focal point of my research. Being part of the Hydrologic Synthesis Project has enabled me to work with an amazing set of colleagues and students, who have, yet again, helped to open up new horizons and expanded opportunities for research, this time based on “comparative hydrology.”

Looking back 30 years I am amazed by how much hydrology has grown and how I have grown with it. Watershed hydrology has enjoyed a great revival, with science and engineering coming together to advance the cause of predictions. Even as I receive this medal, I am delighted to be in the middle of another global initiative, this time on predictions under change, putting humans squarely in the middle of the landscapes we study. For me it has been an incredible journey. Along the way, I have been grateful, indeed blessed, to work with and learn from numerous teachers, colleagues, and students, some of whom are here in this audience. I am grateful to AGU for tonight’s honor, and I thank you all for honoring me through your presence.

Good evening.

—Murugesu Sivapalan, University of Illinois at Urbana-Champaign

Jacob Bear was awarded the 2010 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 15 December 2010 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



It is a pleasure and an honor to introduce Jacob Bear, professor emeritus at the Technion–Israel Institute of Technology, as the 2010 Robert E. Horton medalist. Jacob has had a prime influence on the hydrological sciences and on virtually every scientist who has studied hydrogeology during the past 40 years.

Jacob lists a lifetime of unique accomplishments, and his influence on the field is unparalleled. Jacob has made pioneering, diverse contributions to basic and applied scientific aspects of groundwater hydrology. He began his career in the 1960s acutely concerned by the paucity of tools for quantitative modeling and by the huge gaps in fundamental understanding of the physics of flow and transport in porous media. Jacob has devoted his career to remedying this situation by working to combine basic physical principles, mathematical analysis, and practical applications to produce a coherent and systematic methodology for formulating and quantifying problems in subsurface hydrology. The impact of Jacob’s work has so significantly influenced the field, in so many ways, that it is difficult to enumerate them.

Jacob has had an immeasurable impact through his books, which remain key reference sources to this day. His first book, Physical Principles of Water Percolation and Seepage, in 1968 with S. Irmay and D. Zaslavsky, introduced a comprehensive approach based on mathematical modeling and included among many subjects both saturated and unsaturated (multiphase) flow and solute transport in porous media. This was the beginning of Jacob’s implementation of his concept of “transport phenomena in porous media” as opposed to “movement of water in aquifers.” Indeed, in 1967 and 1969 Jacob organized two international symposia that brought together scientists from many disciplines—hydrologists, soil physicists, reservoir engineers—who had not been communicating previously. As an outgrowth, Jacob’s later books, particularly the 1972 Dynamics of Fluids in Porous Media (which has since been reissued by Dover and has more than 8000 citations), have had a huge impact on the field, and virtually every student and researcher in hydrogeology has studied from Dynamics or referred to it on some occasion. This book changed both theory and practice on a global level. Jacob has also mentored a long list of outstanding young researchers and practicing engineers throughout North America, Europe, and Asia.

Jacob has made benchmark research contributions, notably, to the theory of volume averaging, to quantification of dispersion in solute transport, and to modeling of seawater intrusion (combined with management of coastal aquifers). The latter work dictated management of the coastal aquifer of Israel from the early 1960s and has led to practical improvements in exploitation of coastal aquifers around the world.

As a consequence, Jacob has fundamentally influenced the thinking of at least two generations of hydrologists. Jacob’s conceptual thinking and quantitative approaches have revolutionized the field of groundwater hydrology. Quite simply, Jacob Bear is a legend in his own time. Jacob Bear is a credit to AGU, richly deserving of this highest distinction for outstanding contributions to the geophysical aspects of hydrology.

—BRIAN BERKOWITZ, Weizmann Institute of Science, Rehovot, Israel


I would like to begin by expressing my thanks to those who nominated me for this prestigious award, to those who supported the nomination, to those who selected me, and to Brian Berkowitz for his warm citation.

Many of you, who know me mainly from my books, have no doubt noticed that I am working in two, albeit interconnected, directions: groundwater hydrology and modeling phenomena of transport in porous media. Knowledge of the latter is essential for the former. In addition, this knowledge constitutes the basis for many other engineering disciplines, like geochemistry, petroleum reservoir engineering, chemical engineering, and biomedical engineering. Common to these disciplines is the fact that phenomena of transport of mass, momentum, and energy occur in the special multiphase domain called “porous medium.” The starting point is the use of a magnifying glass to observe and understand what happens at points within the phases and on interphase boundaries and then, by employing homogenization of one kind or another, obtain mathematical models that describe these phenomena in terms of measurable quantities in a domain regarded as a continuum.

An exciting aspect of this area is that it is interdisciplinary. It requires knowledge (and cooperation with experts) in physics, chemistry, continuum mechanics, thermodynamics, and more. All of this knowledge is used to solve societal problems of water resources, energy, and the environment.

Traditionally, groundwater hydrologists have been dealing with extracting groundwater from aquifers while ensuring good quality water and aquifer sustainability. Nowadays, geologists, geochemists, hydrologists, and reservoir engineers join forces to solve environmental problems. An example is carbon dioxide sequestration in deep geological formations, often saturated with brines. Currently, a lot of research and implementation activities are taking place on this exciting subject around the world.

Altogether, I feel lucky to work in the field of hydrology, in which I can combine theory and application, research, and teaching around the world and cooperate with colleagues of many disciplines in contributing to the solution of societal problems—ensuring a sufficient quantity of clean water to the population and ensuring a clean environment.

I cannot close without thanking my many students who helped me, sometimes pushed me, to move ahead, eventually reaching this point.

Finally, I would like to thank my wife, Siona, and my children and grandchildren for being patient when I have been spending with them much less time than they deserve.
Thank you.

—JACOB BEAR, Technion-­Israel Institute of Technology, Haifa

William E. Dietrich was awarded the 2009 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2009 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



It is truly a pleasure to introduce William Dietrich of the University of California at Berkeley as the 2009 Horton medalist for his outstanding contributions to the geophysical aspects of hydrology. That citation pales by comparison with Bill’s accomplishments, for no one comes close to the impact Bill has had in modernizing the field of geomorphology. He maintains the same unflagging energy and creativity in research, teaching, and professional service that have earned him international fame as the most productive, diverse, and influential geomorphologist in the world today.

This influence begins with his superb combination of skill in field observation and his ability to apply mechanistic principles to the analysis of empirical results to construct theories of landscape evolution. His career began with studies of river channel mechanics and of mass wasting in the coastal mountains of Oregon and California. He and his graduate students have extended his discoveries in both of those topics through field studies, laboratory experiments, and analysis of digital topography. They introduced innovations in each field, including high-resolution field measurements of flow and sediment transport, cosmogenic isotope measurement of regolith formation and transport, chemical tracers of floodplain sedimentation patterns, and lidar-resolution measurements of topography. Bill’s group expanded its field, laboratory, and numerical simulation studies to understand regolith formation, runoff processes, sediment transport, channel mechanics, floodplain sedimentation, and bedrock incision by streams and debris flows, typically being the first investigators to demonstrate the utility of a technique for extending landscape theory. Their studies continue to expand into hyperarid landscapes, including Mars.

The novelty and range of Dietrich’s studies begin with his innate curiosity about landscapes and their relevance for humans and other biota. He constantly shares his knowledge openly, and he is relentlessly inquisitive about other disciplines. His friendly demeanor and generosity, especially with young scientists, make him a hero in the discipline, and induce similar behavior among his large and productive group of former graduate students.

Bill is an exemplar of the AGU commitment to “unselfish cooperation in research.” He worked tirelessly within the Erosion and Sedimentation Committee of the Hydrology section to promote geophysical approaches in geomorphology, and to organize special sessions with other sections, leading to seminal interdisciplinary initiatives. These efforts continue and have expanded into other community-building efforts such as the National Center for Earth-surface Dynamics, the National Center for Airborne Laser Mapping, and National Research Council and National Science Foundation committees. His most influential community-building activity must surely lie in organizing the Gilbert Club, an annual gathering of geomorphologists that he established in 1983. At that event, Bill is at his tireless best—reporting scientific results, asking penetrating questions, including specialists from other fields, promoting the role of young researchers, making sure the program runs and that someone has ordered lunch and dinner—essentially driving the field forward with his physical and intellectual energy.

Bill is a model for all we aspire to be as members of this Union, and as worthy a recipient of the Robert Horton Medal as I can imagine.

—THOMAS DUNNE, University of California, Santa Barbara


Robert E. Horton is a hero to all geomorphologists. He lit the candle that guided us to quantitative inquiry. He observed, quantified, analyzed, performed field experiments, and proposed theories linking hydrology, erosion processes, and form. His 1945 Geological Society of America paper is beyond a “classic”—if a “classic” is defined as a paper often cited but never read. Horton’s paper still now, in 2009, deserves reading and rereading.

I remember well when I was introduced to Horton’s work and to geomorphology as a whole by Tom Dunne in the early 1970s. Geomorphology was considered by many then as an uncomfortable, backward cousin of Earth science, taught only in introductory classes, and lacking in quantitative accomplishments or rich research opportunities. Tom knew differently and opened the eyes of a generation of students.

Things could not be more different now. I have been witness to, and had some hand in, the rediscovery of geomorphology. Our field is populated with generous souls who collaborate closely, share their knowledge, and inspire their students. My colleagues have started new journals, organized new centers, invented new methods of observation, participated in committees and workshops, and written those reports that have created opportunity in our field. The Hydrology section of AGU in particular has been consistently supportive, encouraged new developments, and welcomed this emergence of geomorphology. I must note, too, that the section has been exceptionally kind to me throughout my career.

I thank my many collaborators who have continually challenged me, pulled me, and given me opportunities to learn from the best minds. Berkeley is a magnet for ambitious, creative students, and I have had the great fortune of working with many students with exceptional talent. When I opened a door to a room, they would fill it with intellectual furniture beyond my imagination. If chance favors the prepared mind, then I thank in particular Tom Dunne and Jim Smith, my graduate advisors at the University of Washington, for preparing me for what has been a surprising, exciting time of discovery. I share this medal with all of those from whom I have learned so much. And I must also share this medal with Mary Power, my wife, the warm soul who keeps me tethered as I wander this lovely field in search of the new.

—WILLIAM E. DIETRICH, Department of Earth and Planetary Science, University of California, Berkeley

Vijay K. Gupta was awarded the 2008 Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, held 17 December 2008 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



The AGU Robert E. Horton Medal represents the pinnacle of achievement in the field of scientific hydrology. Today, one of hydrology’s visionaries, Vijay Gupta, receives this unique honor for his fundamental contributions to the evolution of hydrology as a geophysical science. I am proud to deliver this citation.

After completing his Ph.D. in 1973, Vijay embarked on a long odyssey of scientific discovery through the whole of the hydrological landscape. From the outset, he recognized the fundamental importance of scale. It became a pervasive theme in all his work, which has ranged uniquely from the molecular to the planetary scale. Throughout, Vijay has eschewed the traditional, safer, specialist route with assured incremental progress for more integrative and risky directions that can redefine the field through unforeseen but enduring advances.

Vijay’s early work with mathematician Rabi Bhattacharya and soil physicist and Horton medalist Gary Sposito led him to develop an understanding of multiscale dispersion of solutes in aquifers based in molecular dynamics. It provided an important foundation for subsequent work in the field. The mathematical elegance of this body of work became a hallmark of all of his research. His parallel work with mathematician Ed Waymire on space-time rainfall variability on multiple scales has impacted the field for more than two decades. Vijay’s recently published paper on understanding the physical basis of statistical clustering and scale invariance in rainfall lays a foundation for modern hydrometeorology.

His major excursion into geomorphology led him to derive generalized Horton laws for the rescaled full probability distributions of drainage areas and stream lengths for a new class of random self-similar networks. This groundbreaking work was to lay the foundation for his research on a multiscale geophysical theory of floods in river basins. It was largely inspired by a question posed by Dave Dawdy: “How can we understand the geophysical basis of regional annual flood statistics widely used in engineering?” Building on his research results for idealized basins, Vijay has established the multidisciplinary, multiscale Hydro-Kansas experimentation program in the Whitewater Basin, Kansas, to test some new hypotheses.

The hypothesis of self-regulation underlying the Gaia theory of Lovelock and Margulies fascinated Vijay immensely. In a recent paper, he showed the strength of negative feedbacks from the hydrological cycle in regulating the planetary climate for a warming Sun.

As an encapsulating tribute to Vijay’s research, the following quote from Horton’s biography seems particularly apposite: “…his continual thinking across disciplinary lines and his continual interplay between engineering practice and scientific curiosity…”

Over the past two decades, Vijay has unselfishly mobilized or led major community research initiatives. Most notable among these is the “Water, Earth, Biota (WEB)” visionary report, an implementation plan for Opportunities in the Hydrologic Sciences, which spawned the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI). He also inspired the launch of the International Association of Hydrological Sciences decade on Prediction in Ungauged Basins (PUB).

Vijay is always ready to share ideas, philosophy, and time with those who seek his advice and leadership, and many have. His calm but assured manner and clear analytical thinking empower others. All will applaud the award of the Horton Medal to this inspirational scientist and engineer.

—EDNA O’CONNELL, University of Newcastle upon Tyne, UK


Thank you, Enda, for your generous citation. I acknowledge all who supported my nomination, AGU, and the medal committee, for this honor.

The Robert E. Horton Medal is the most visible milestone in my uncharted academic journey that began exactly 40 years ago. Cooperation from numerous colleagues and students made it possible. I enthusiastically share this medal with all of them.

Joining a unique statistical hydrology program under Vujica M. Yevjevich at Colorado State University in 1968 was a great beginning. My early association with Dave Dawdy blossomed into a lifelong collaboration and friendship. My move to the University of Arizona in 1971 was exciting and challenging. The untimely passing away of my advisor, Chester Kisiel, served as a catalyst to explore “risky directions” rather than follow a “safer, specialist route.” For example, I was drawn to Rabi Bhattacharya and Gary Sposito for their originality and brilliance. Therefore, I moved away from my dissertation topic of rainfall and began a serious collaboration in subsurface hydrology with them. I acknowledge Sol Reznick for his foresight to encourage and support our collaboration. Three foundational ideas unified our research: (1) the link between physical processes, statistical variability, and geometry, (2) asymptotics and limit theorems, and (3) scale invariance and scale dependence. They became a road map to all my joint research.

My collaboration with Ed Waymire at Ole Miss flourished because of his dedication and clarity for mathematical applications in sciences. The nurturing environment was pivotal that administrators like Karl Brenkert, Allie Smith, and Pete Wagner created. We greatly appreciated Steve Mock of the Army Research Office for funding our unconventional ideas. My rude awakening to the “real world” occurred after joining the University of Colorado in 1989. But I was very fortunate to expand my research opportunities while facing ever growing challenges, locally.

I acknowledge all of my national and international collaborators from hydrology, engineering, physics, geophysics, statistics, geomorphology, fluid mechanics, meteorology, and ecology, who became an integral part of a highly interdisciplinary multiscale research agenda. Many outstanding students, from Oscar Mesa to Ricardo Mantilla, representing different disciplines became the backbone of my research.

In 1984, the sudden elimination of the National Science Foundation’s [NSF] hydrology and hydraulics grants program from the Engineering Directorate was a major setback, which fueled my persistent community service efforts. I acknowledge the team effort from Pete Eagleson (Massachusetts Institute of Technology) for his leadership, Marshall Moss (U.S. Geological Survey), Ignacio Rodriguez-Iturbe (Princeton University), and others who brought about a new hydrology grants program in the Geoscience Directorate. I especially recognize Doug James (NSF), and numerous colleagues, whose wisdom and hard work contributed to our collective efforts on “Water, Earth, Biota” to guide this program.

My next frontier is to develop a unified theory that views “life” as the basic link between “geophysiology” and “consciousness.” As water is essential to life, the global water cycle is the key to understanding environmental self-regulation. I grasped the profound connection between consciousness and life after years of guidance from a contemporary Indian philosopher, Tatvagyani Vethathiri. I have no words to give him due reverence.

I am privileged to inherit the legacy of my father, a hydraulics research engineer, and my love for mathematics from my mother, which made this journey possible.

My gratitude to my wife, Indira, is unmatched for being who she is.

—VIJAY K. GUPTA, University of Colorado, Boulder

Rafael L. Bras was awarded the 2007 Robert E. Horton Medal during a special presentation at the AGU Fall Meeting Honors Ceremony, held 17 December 2008 in San Francisco, Calif. The medal is for “outstanding contributions to hydrology.”



I am extremely happy to introduce Rafael L. Bras, winner of the 2007 AGU Robert E. Horton Medal. There is no doubt in any hydrologist’s mind that Bras is superbly qualified for this award. His combination of breadth and depth in the coverage of multiple fields in the hydrologic sciences has earned him a place among the most distinguished hydrologists of the past half century.

Rafael is dean of engineering and distinguished professor of civil and environmental engineering at University of California, Irvine. Until recently he was the Edward Abdun-Nur Professor of Civil and Environmental Engineering at Massachusetts Institute of Technology (MIT), where he also had a joint appointment in the Department of Earth, Atmospheric, and Planetary Sciences. His leadership in the hydrologic sciences has been superb. He is the author of two textbooks widely used throughout the world and of over 160 papers in major journals with many more in books and conference proceedings. This is indeed an outstanding scientific production; nevertheless it wouldn’t mean much if it were not for the truly magnificent quality of Rafael’s contributions. It is marvelous how he covers such a wide range of topics in water science and technology with the impressive depth of knowledge and creative thinking that he displays in all of his work. I had the privilege of being his Ph.D. advisor and remember very well that my recommendation when I left MIT, to the then department head, Peter S. Eagleson, was to bring Rafael back from Puerto Rico to take my position. I assured Pete on how much the Institute would win with the trade! I am proud that I was indeed correct in my prediction and that Rafael has become a world leader of the field and a source of inspiration and pride for MIT, the University of California at Irvine, and his friends.

Without going into full details about his multiple and outstanding research contributions, I want to mention that Rafael has made pathbreaking research in hydrologic network design, urban storm water management, forecasting of hydrologic series, rainfall modeling, optimal operation of water systems, irrigation control, soil-atmosphere interaction, ecohydrology, and the fractal structure of drainage networks. In all of these areas, Rafael has left a permanent impact throughout research that is uniformly excellent, characterized in all cases by a wonderful choice of problems, and full of creative and imaginative ideas.

Rafael’s excellence in research has brought him numerous distinctions nationally and internationally. In the United States he has received multiple awards from the American Society of Civil Engineers and the American Meteorological Society. He is also a member of the National Academy of Engineering and a recipient of the Clarke Prize, for outstanding achievement in water sciences and technology. The American Geophysical Union has distinguished him with the Hydrologic Sciences Award and the James B. Macelwane Medal. The number and quality of his students is also impressive. They are all over the world occupying leadership positions in academia, major corporations, and government organizations.

Even a full recital of Rafael’s unique achievements would not convey an appropriate description of what is most important in him: the qualities of his character, his love for his family, his honesty, and his genuine care for the advancement and equal treatment of all people. It has been my great privilege to have been his friend for 35 years as well as to share in the love of his wonderful family, Pat, Rafael E., and Alejandro, who occupy a very special place in the heart of my own family.

—IGNACIO RODRIGUEZ-ITURBE, Princeton University, Princeton, N. J.


Some years ago I gave a talk entitled “Everything I learned wrong at MIT.” This title was meant to be a tongue-in-cheek provocation, but the content was serious. Hydrology has evolved so much that nothing I do now I learned at that time. It could not have been a better time for a hydrologist; I have had the license to explore with the necessary luxury of being able to be wrong once in a while. That the land hydrologic cycle could be inherently linked and important to the atmosphere was considered ridiculous until fairly recently. Interpreting nature as a product of both chance and necessity and discovering the physical basis of apparently random behavior opened the door to a whole new set of methodologies. We started doing optimal estimation and data assimilation 30 years ago, and now it is operational in atmospheric sciences and hydrology. Reinterpreting the observations of Horton about the organization of river basins as fractals was the breakthrough needed to inspire a few of us to seek a mechanistic explanation of why such organization occurs, and to explain and predict how the landscape evolves in a tightly choreographed dance with water flow, sediment transport, climate, and vegetation. The term ecohydrology did not exist when I was a student. But now we have come to the realization that all hydrologic processes are mediated, if not controlled, by the biosphere. I could go on, but suffice it to say that I have lived a true revolution. Back in 1987 Pete Eagleson and I wrote a piece for Eos entitled “Hydrology: The forgotten science.” Well, it is not forgotten anymore; it is established and valued. I have been honored to play a small role in that revolution, and I have loved every minute of it.

No one succeeds in life alone, and in my case I have been truly fortunate to have the proverbial village behind me. My life is full of opportunities taken, opportunities that were created and introduced by a very large number of people. Twenty-two other individuals received this medal before me. These are the people who built modern hydrologic sciences. To have known many of them and be considered part of this august group is humbling. But I have been further blessed by counting some of them and others among my mentors and good friends. I have to mention Ignacio Rodriguez-Iturbe, Peter Eagleson, and the late Donald Harleman. Without their advice and care I simply would not be here.

My wife, Pat, and our sons, Rafael E. and Alejandro, are always my fellow adventurers. Thank you for never letting me forget the important things of life.

All professors know that their success is due to their students. I have had over 50 students in the MIT “Bras Group.” To them I dedicate this medal; they are the best, and also the most fun. I am looking forward to having another 50 students at my new academic home, the University of California, Irvine. To all past and future students, please remember that many times it is better ultimately to be proven wrong than to be boring. Be bold and carry on with the revolution.

—RAFAEL L. BRAS, University of California, Irvine

Thomas Schmugge was awarded the Robert E. Horton Medal at the AGU Fall Meeting honors ceremony, which was held on 13 December 2006 in San Francisco, Calif. The medal recognizes outstanding contributions to hydrology.



For the past 30 years, Thomas Schmugge has been a truly peerless intellectual leader in improving both the theory and the application of microwave and infrared radiative transfer for the remote sensing of the land surface, especially soil moisture, surface temperature, and emissivity. Without exaggeration, he has been a trailblazer and is now unquestionably one of the few world experts on remote sensing in hydrology.

He already made his mark in the early 1970s in the remote sensing of soil moisture, snow, and sea ice. In a seminal paper, he was the first to recognize how soil texture affects microwave emission. He then succeeded in developing a theoretical framework explaining how the bonding between water and colloids affects the soil’s dielectric properties. With this he pioneered a model to predict the variation of the dielectric properties of soils in terms of soil moisture; this model is in wide use as the standard method today.

Subsequently, he initiated leading-edge studies to put the relation between the diurnal range of surface temperature and soil moisture on a more quantitative basis; this led to the successful HCMM [Heat Capacity Mapping Mission] satellite experiment in 1978. His work with the thermal IR data from the HAPEX [Hydrologic-Atmospheric Pilot Experiment] experiments in 1986 and 1992 demonstrated how the spectral variation of surface emissivity for both bare and vegetated surfaces can be determined remotely. This work led to his selection as a team member on the U.S./Japan science team for the multispectral ASTER [Advanced Spaceborne Thermal Emission and Reflection Radiometer] instrument for NASA’s Earth Observing System satellite Terra, launched in 1999. Most recently, ASTER data have been used to map the surface emissivity of large arid areas, and these maps are being implemented with great success in climate models to improve the accuracy of the predicted soil moisture, surface temperature, and surface fluxes of latent and sensible energy.

Tom Schmugge has been a tireless catalyst and pathfinder in a number of largescale field experiments applying these techniques to map surface soil moisture. These include HAPEX-Mobilhy in 1986 in southwestern France, FIFE in 1987 in Kansas, Monsoon 90 in Arizona, the Washita 92 experiment in Oklahoma, and the HAPEX-Sahel experiment in 1992 in West Africa. Moreover, in several of them he led the analyses of the microwave radiometer data. His work proved that microwave sensors can determine the soil water content of the 0 to 5 centimeter layer through vegetative canopies up to and including a mature corn crop, with natural surface roughness having only a small effect; it also showed how soil evaporation and soil hydraulic properties can be estimated with such repetitive microwave observations. Schmugge’s approaches are increasingly being implemented by others in this country and abroad to map soil moisture globally, and his findings are already having wide ramifications, generating new data sources from space for use in crop production, atmospheric circulation studies, and runoff forecasts.

The Robert E. Horton Medal is awarded for “outstanding contributions to the geophysical aspects of hydrology.” Schmugge’s accomplishments perfectly embody this ideal. His research has dealt with soil moisture and radiation, the main drivers of the Earth’s energy and water budgets. Moreover, his leadership in remote sensing within AGU and in promoting hydrologic-atmospheric experimentation has been of critical relevance to our science. I cannot think of anyone more deserving of the Horton Medal than Thomas Schmugge.

—WILFRIED H. BRUTSAERT, Cornell University, Ithaca, N.Y.


Thank you, Wilf, for your kind and generous introduction. This is a great honor for me, and I also look upon it as recognition that remote sensing can make a contribution to hydrological problems.

As you noted in your acceptance of the Robert E. Horton Medal a few years ago, you had the good fortune of being in the right place at the right time. This is also true in my case and played a large part in my being here today. I was trained as a solid state physicist across the bay at the University of California, Berkeley, and in the late 1960s when I was looking for a position, none was to be found in that field. So I decided to explore the use of my microwave background in the new field of remote sensing and applied to NASA for a U.S. National Academy of Sciences postdoctoral position. It turns out that Bill Nordberg, a leader in NASA’s Earth observation program at the Goddard Space Flight Center (Greenbelt, Md.), was looking for someone to explore the use of microwave radiometers for land remote sensing. This was just before NASA was to launch its first microwave radiometers on the Nimbus 5 satellite. Our initial studies indicated that both soil moisture and snow had interesting microwave signatures. The soil moisture work was more appealing to me. After more than 30 years of work on the use of microwave radiometers for soil moisture sensing, I am heartened by the prospective launch of the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) mission next September. I am discouraged, however, by the fact that NASA did not approve its prospective soil moisture mission, Hydros, after several years of studies.

I would like to thank the many colleagues I have worked with over the years in the Hydrological Sciences Branch at NASA Goddard Space Flight Center and the U.S. Department of Agriculture/Agricultural Research Service Hydrology Laboratory, Beltsville, Md., without whose support and collaboration I would not be here today. In particular I would like to mention Tom Wilheit, my office mate early on at Goddard, who taught me microwave radiometry, and Tom Jackson at the Hydrology lab, who showed me the importance of soil moisture to hydrology.

In closing, I want to express my gratitude to AGU for bringing us together and providing a forum for the discussion of geophysical results and to the members of the Horton Medal Committee and the others who supported my nomination.

—THOMAS SCHMUGGE, New Mexico State University, Las Cruces

Gedeon Dagan was awarded the Robert E. Horton Medal at the 2005 Fall Meeting Honors Ceremony, which was held on 7 December, in San Francisco, Calif. The medal is given for outstanding contributions to hydrology.



“I am proud to introduce Gedeon Dagan, Emeritus Professor at the Tel Aviv University [Israel], as the recipient of the 2005 AGU Robert E. Horton Medal. Gedeon’s contributions redefined the science and the practice of subsurface hydrology in a period spanning the past three decades, having been a major player in, if not the originator of, some of the most significant breakthroughs in this field. As a result of his work in particular, the entire discipline experienced a major transformation toward a more solidly theoretical Earth science.

“Gedeon Dagan has contributed fundamental advances to stochastic modeling of a broad range of natural phenomena related to subsurface hydrology. On an occasion like this, it is impossible to do full justice to the impact of his work; therefore I will merely enumerate some of the areas of his more important contributions.

“The statistical characterization of aquifers and soil properties, including the description and identification of the relevant aquifer features ruling flow and contaminant transport in the subsurface; the prediction of spreading of solutes in heterogeneous aquifers, where his Lagrangian model has become a classic tool and a reference to all the other theoretical formulations developed since its appearance; effective properties of subsurface systems, with Gedeon’s classic results on the effective conductivity of heterogeneous media; travel time analysis of transport, which was given a strong scientific foundation by Gedeon in the early 1990s, shedding new light in the way transport processes were modeled at that time; the general idea of effective spreading, where the interplay between the pollutant and the heterogeneity length scales plays a crucial role in the transport dynamics; nonuniform flow toward wells in heterogeneous formations, which is an extremely complex and still quite unexplored topic; and water and contaminant dynamics in highly heterogeneous porous formations, going beyond the linear theories of transport and moving into the fascinating world of nonlinear, highly complex systems.

“Breadth and depth are the main features of Gedeon’s work, jointly with rigorous methods, the relevance of the issues addressed, and the cultural bridges among different disciplines. The vastness of Gedeon’s knowledge and of his scholarly pursuits is demonstrated by his extraordinary publication record. It pleases him very much to be included, and we much admire his inclusion in the International Scientific Institute (ISI) Highly Cited Researchers short list, indeed a major achievement among the many recognitions he has received, among which the Stockholm Water Prize has a unique place.

“Gedeon’s enthusiasm and energy make him an extremely important resource to students and scientists who have benefited, and continue to benefit, from his activity. The many students and colleagues who had the opportunity to meet and work with Gedeon recognize the most distinctive features of his character, like his brilliant mind, his creativity, his generosity in sharing ideas and knowledge with younger persons, his advice, and his restless devotion to truth and excellence in research.

“In summary, Gedeon’s outstanding scientific and engineering contributions, his enthusiasm for learning, his capability to cross frontiers and open new boundaries in hydrological research, and his fresh creativity merging knowledge from different disciplines have put him at the very top of the scientific enterprise. Gedeon’s drive to excel and his enthusiasm for research are examples that rarely find equals. Gedeon Dagan is certainly most deserving of the recognition carried by the highest distinction that AGU grants to hydrologists, the Robert E. Horton Medal.

—ALDO FIORI, Universitá di Roma Tre, Italy


“Thank you very much, Aldo, for your wonderful citation. Although it overstates my achievements, I know it is a sincere expression of friendship that emerged from a long and fruitful collaboration.

“It is customary to devote such a reply to thanking all those who have helped me and made possible this recognition of my work. I thought I may rather use the occasion of addressing a distinguished audience of members of different AGU sections to talk briefly about hydrology. I therefore thank collectively my family, and first of all my wife, Ora, who is present here, and the many friends and colleagues I have acquired during my career.

“My first thesis is that hydrology is one of the oldest professions in the world. This reflection was caused by accident, like many other discoveries, due to a visit to a fascinating archeological site in Israel, at Tzipori, near Nazareth. This was a flourishing town during the Roman and Byzantine periods. One of the interesting and enigmatic remnants dug up recently is a beautiful mosaic called ‘The Nile Festival,’ which dates from the Byzantine period, fifth century. It portrays a legendary Nile populated by different beasts, an Amazon, and the detail shown in Figure 1, which depicts in a symbolic manner the construction of a Nilometer. This is a marked pillar that served to measure quite accurately the level of the Nile.

“The first Nilometers and mention of their level records go back to the third millennium B.C. and even earlier. The fertile Nile valley made possible the existence of the ancient Egyptian civilization. The readings were used by the hydrologists of the Pharaohs (persons of high standing, most probably priests) in order to predict periods of drought or floods, both detrimental to agriculture. In turn, these analyses and predictions were employed in order to fix the level of taxation of the population and the storage policy.

“My second thesis is that ancient and modern hydrology share a common ground. Thus, there are four constituents of ancient hydrology that are shared by the modern one:

Hydrology is a quantitative discipline. It deals with data and with mathematical analysis.
Hydrology is an applied science. The motivation and aims were related to the needs of society.
Hydrology deals with prediction under uncertainty. The ancient hydrologist had to use sophisticated time series analysis in order to predict occurrence of extreme events.
Hydrology is intertwined with economic, political, and social issues. Predictions had a serious impact on the sustainability and well-being of society.
“My work on contaminant transport by groundwater, which takes place in an environment of a complex spatial structure that calls for analysis by advanced tools, shares these four ingredients with ancient hydrology.

“Thank you for your patience in following this condensed story about hydrology over a span of 5000 years.”

—GEDEON DAGAN, Tel Aviv University, Israel

Garrison Sposito received the Horton Medal at the 2004 Fall Meeting Honors Ceremony on 15 December, in San Francisco, California. The medal is given for outstanding contributions to hydrology.



It is a great pleasure to introduce Professor Garrison Sposito of the University of California, Berkeley as the 2004 AGU Robert E. Horton Medalist. Those of us who know Gary well already recognize him as an undisputed leader in the field of hydrology. Gary’s extensive scientific contributions in geochemistry, thermodynamics, mathematics, and subsurface hydrology are legendary. He is largely responsible for bridging the areas of aqueous geochemistry and physical hydrology. Andrew Barry commented that “there is simply no other hydrologist who brings such a mastery of theoretical physics and chemistry to bear on hydrologic problems.”

Wilfried Brutsaert summarized Gary’s overall contribution as one of intellectual leadership and integrity in the field of hydrology, through his development of the physical and chemical bases of soil hydrology. In a field that often suffers from an overemphasis on operational methods, Gary is one of the very few who, some 40 years ago, took a fundamental approach to solving hydrologic problems. His work covers an incredibly broad range of frontline research areas and bears witness to his penetrating scientific insight. Gary’s writing style is extraordinarily lucid; he has a gift for making deep theoretical issues understandable to the broader scientific community.

Gary’s work on scaling is one of his many contributions to physical hydrology that has a thoroughness rarely achieved. Starting with the scaling of spatial variability in partly saturated soils, he advanced into the relevance of the fractal nature of soil water properties and more recently formulated a complete theory of the significance of ergodicity in the fundamental construct of the spatial scale. His theory for solute transport in heterogeneous formations generalized existing results and allowed for the prediction of macrodispersion coefficients. Gary’s continued emphasis on “putting the physics into soil physics” is an inspiration for all of us.

Gary helped establish another cornerstone in hydrology by linking physical chemistry with hydrology. James Morgan pointed to the clarity and rigor of Gary’s work on the ion exchange properties of soils and the characterization of the surface chemical properties of metal oxide particles in water. He has done pioneering research on adsorption isotherms, statistical mechanical foundations of surface equilibria, and electrical properties of solid/ aqueous interfaces. And William Casey notes that other geochemists often rely upon Gary to do the “heavy lifting” of interpreting their observations. Gary’s formidable breadth of work has led to new scientific insights that extend into microbiology and ecology.

Gary’s interests are also reflected in his important scholarly books ranging from quantum physics and classical dynamics to thermodynamics and the chemistry of soils. The incredible span of Gary’s contributions would make a small army of researchers internationally known—yet he is a single individual.

As many of us have experienced, Gary is a scholar with an enormous heart and an uncommon graciousness toward younger scientists, offering invaluable help in the form of mathematical derivations and detailed explanations. For his “spirit of helpfulness and friendliness in unselfish cooperative research,” we can think of no more deserving recipient of the Horton Medal.

—MARC B. PARLANGE, L’Ecole Polytech Federale Lausanne, Switzerland


Thank you, Marc, for your very kind words, and thank you, my colleagues, for this splendid honor.

One November afternoon, during the halcyon days of my tenure at our Riverside campus, I was paid a visit by the soil physicist, Lorenzo Richards, who called on me after reading the dissertation of my first doctoral student, Juan Giráldez, in which an attempt was made to find a covariant form of Richards’ celebrated partial differential equation describing water flow in an unsaturated porous medium. I learned that afternoon about the near-rejection of Richards’ paper in which his famous equation was introduced and of his continuing wonder over the 50 years since its publication that his work could be so influential. He was especially bemused at the naming of the equation by his colleagues and by its exegesis in the literature of hydrology. That there could be a deeper significance than operational in his equation had simply not occurred to him.

Richards’ preoccupation was in fact with the measurability of the hydraulic conductivity as a function of matric potential. In field soils, both properties are inexorably variable, thus reflecting the vicissitudes of heterogeneous texture and structure. But suppose now that a simplifying hypothesis is made: that the underlying cause of this spatial variability is not related to the mechanistic underpinnings of how water flows. If this is true, then the physical law governing flow must itself be uniform across a field, and this implies a similar uniformity in the functional relationship mentioned above, in the sense that it is quantified by the same parametric equation everywhere in the field. Once the physical law is expressed as a partial differential equation whose spatial uniformity is invoked, a strong constraint is placed on the mathematical forms permitted for its variable coefficients, making this conclusion inescapable.

Formally, one says that the Richards equation then exhibits scale invariance, with Lie group theory applied to show that the hydraulic conductivity can have only a power law dependence on matric potential. Physically, one says that the mechanism of water flow then has no intrinsic length scale, a matter which must be left for field experimentation to decide. The Gardner soil stands as a powerful reminder that nature need not conform to such perfect symmetry (think of the entrance to Notre Dame de Paris).

This necklace of thoughts is meant simply to convey a preoccupation with searching for a certain order in chaos, typified by scale invariance and, most recently, topological structures, in subsurface flows. I was so fortunate to have two early mentors, Duwayne Anderson and Kenneth Babcock, from whom to learn this abiding theme in the context of soil physics and chemistry. Tom Anderson, in a course we co-taught 35 years ago, introduced me to the broader realm of hydrology, and Vijay Gupta, in a collaboration begun 30 years ago, opened the gateway to unified theory. My wife, Mary, and my six children, Doug, Dina, Frank, Jennifer, Sara, and Cris, have sustained this journey with a joy beyond measure.

—GARRISON SPOSITO, University of California, Berkeley

Shlomo P. Neuman was awarded the Horton Medal at the AGU Fall Meeting Honors Ceremony, which was held on 10 December 2003, in San Francisco, California. The medal honors “outstanding contributions to hydrology.”



“I am proud to introduce Shlomo P. Neuman, Regents’ Professor of Hydrology and Water Resources at the University of Arizona, as the 2003 AGU Horton Medalist. Shlomo’s contributions to subsurface hydrology helped define the science and its practice in the last 40 years. He is uniquely deserving of the Horton Medal.

“Shlomo’s research centers around theoretical, computational, and field analyses of fluid flow and solute transport in porous and fractured geologic media, reflecting a philosophy according to which hydrology requires the application of rigorous thinking to complex scientific and engineering problems. He conducts his research within a rigorous theoretical framework nevertheless applicable to real-world problems. His approach has led to major advances in our understanding of flow and transport processes under a broad range of field conditions, within a wide range of hydrogeologic environments, that are of both scientific significance and practical relevance; and in our ability to describe and generalize such processes mathematically, simulate and analyze them computationally, and measure and observe them in the field.

“Shlomo’s unique approach stems from his undergraduate education in geology and his graduate education in engineering. His M.S. work at UC Berkeley led to an elegant solution for flow through aquitards and the Neuman-Witherspoon ratio method to determine their hydraulic properties. His doctoral work resulted in a hydrodynamic theory of multiaquifer systems verified through a month-long pumping test spanning five formations under Oxnard, California. His early work on finite elements helped launch the era of computer flow simulations and explore the terra incognita of flow in the vadose zone. The Neuman method of analyzing flow to wells in unconfined aquifers has become the standard of the profession. Shlomo and his students and collaborators have made seminal contributions to hydrogeologic simulation, inverse theory, fractured rock hydrology, stochastic subsurface flow and transport theory, and hydrogeologic scaling. He pioneered the concept of hydraulic tomography and, with his students, used pneumatic tests to acquire the first fully three-dimensional tomographic images of permeability and porosity in the subsurface.

“Shlomo is an outstanding teacher and educator, many of whose students have become leaders in their fields. Thanks to Shlomo and his students, the University of Arizona Ph.D. program in hydrogeology consistently ranks best in the nation.

“I would be remiss not to comment on Shlomo’s remarkable personal history. Born in Czechoslovakia at the outbreak of World War II, Shlomo was interned by the Nazis only to discover later that his father and the vast majority of his extended family had perished in the Holocaust. He and the remnants of his family sought haven in Israel, where Shlomo acquired his undergraduate degree. He met his lovely wife, Yael, as a graduate student at U.C. Berkeley and, following a 4-year sojourn in Israel, his family settled in Tucson, where Shlomo continues to teach and churn out new ideas.

“For his outstanding contributions to hydrologic science, education, and practice I am proud to present the most highly deserving recipient of the 2003 Horton Medal, Shlomo P. Neuman.”

—SOROOSH SOROOSHIAN, University of California, Irvine


“Thank you, Soroosh, for your generous introduction. I am thrilled and humbled to be a recipient of this prestigious medal.

“My interest in hydrogeology was sparked by pioneering Israeli water projects of the 1960s. A warm letter of acceptance from a future Horton Medalist, Paul Witherspoon, enabled me to pursue an M.S. degree in geological engineering at U.C. Berkeley. There I was greeted by a future Macelwane Medalist, Al Freeze. What better induction into the field could one hope for? What good fortune would soon guide me to cross paths with my future wife and life companion, Yael? It is she who deserves the credit for my decision to pursue doctoral studies and a lifetime career of academic pursuit. Her unfailing support and understanding have earned her a full share of the honor bestowed on me today.

“With Paul Witherspoon I learned to appreciate the power of mathematics and computation in addressing fundamental and real-world hydrogeologic problems. The late Eshel Bresler and colleagues at the Agricultural Research Center in Israel helped kindle my interest in soil physics and the emerging field of vadose zone hydrology. Reinder Feddes of Wageningen Agricultural University helped open my eyes to the role played in hydrology by plants. Ghislain de Marsily and colleagues at the Paris School of Mines helped ignite my fascination with geostatistics and inverse problems. The opportunity to join a unique department fully dedicated to hydrology and water resources, aided by delay in an eventual offer of tenure from the Weizmann Institute of Science in Israel, led me to the University of Arizona. There I enjoyed early years of collaborations with the late Sid Yakowitz and Gene Simpson, and more recent years with Pete Wierenga, on a host of fascinating theoretical and experimental field projects championed in part by U.S. NRC project managers John Randall, Tom Nicholson, and Ralph Cady. My greatest reward came from close interaction with many unbelievably brilliant and wonderful young people who have helped produce much of the science recognized here today. The honor is theirs as much as mine. Since my younger collaborators are too numerous to name, the least I can do is tell them: Thank you for the privilege of having worked with you; I greatly appreciate the intellectual challenge and sheer pleasure of continuing to conduct joint research with some of you; I cherish your friendship and am immensely proud of our joint and your individual accomplishments. I am especially thrilled that one of you, Jesus Carrera, has been named 2004 Henry Darcy Medalist by the European Geophysical Society’s Hydrological Sciences Section.

“In the last several decades, major advances have been made in our understanding of hydrologic phenomena and our ability to interpret some of them within a self-consistent theoretical framework. A major remaining challenge is to extend and unify this phenomenological and theoretical understanding across the field so as to combine our somewhat disjoint subdisciplines into a more fully integrated and rigorous hydrologic science. I am personally most excited about steps already taken toward such integration in the areas of hydrologic simulation, uncertainty analysis, and scaling.

“I am deeply indebted to friends and colleagues who initiated and supported my nomination, and to members of the Horton Medal committee for their trust in the value of my contributions to hydrology. Thank you all for this wonderful honor.”

—SHLOMO P. NEUMAN, University of Arizona, Tucson

Jean-Yves Parlange was awarded the Horton Medal at the AGU Fall Meeting Honors Ceremony, which was held on 10 December 2003, in San Francisco, California. The medal honors “outstanding contributions to hydrology.”



“It was in 1969 that Jean-Yves Parlange had his ‘road to Damascus’ experience on that fateful day in the Yale library, when he happened to come across a recent paper on nonlinear diffusion, as applied to soil water seepage. It immediately struck him that there had to be a better and more efficient way of approaching this problem. He plunged right in, never looking back, for it seems he had found his true calling. Over the next three decades, Jean-Yves Parlange established himself as a pioneer in soil water hydrology, and he is now recognized as an undisputed intellectual leader in our field. He is especially renowned for his penetrating analytical insight into uncovering the physical and mathematical basis for a deeper understanding of soil hydrologic behavior.

“His countless contributions to the literature have covered an incredibly broad range and have consistently been of a quality and thoroughness most of us can only dream of achieving. On an occasion like this, it is impossible to do full justice to the real impact of his work; therefore, I will merely enumerate some of the areas of his more important contributions.

“Even before he entered hydrology, he had already formulated stability criteria for chemical diffusion in laminar flows near flame interfaces. For this work, he received in 1962 the prestigious Minta Martin National Award by the Institute of Aerospace Sciences. Early on, he also showed his mettle in surface tension physics, as related to homogeneous nucleation during phase transition in a gas, and to the movement of deformable drops and bubbles.

“After he entered hydrology, he explored the convective-dispersive equation and the impact of boundary and initial conditions on solute transport in porous materials. Through observations, backed up by theoretical boundary layer considerations, he and his associates elucidated the thermal exchanges between a leaf and the atmosphere. Together with his associates, he was equally successful in clarifying overland flows, by extending the kinematic wave approach, to analyze situations with converging/diverging surfaces, surface curvature, and shocks.

“Building on his earlier work on flame stability, Parlange directed his attention to wetting front instabilities in soils; such instabilities can result in rapid water and solute movement over great distances and can have major implications for the hydrology of waste disposal, fertilizers and pesticides, fingering of water through oil spills, and the effects of surfactants in soil remediation. Jean-Yves Parlange quickly realized that hysteresis is a key mechanism in these instabilities and developed a parameterization that yields all possible scanning curves. I found it to be the most effective formulation among the available approaches. Parlange and his co-workers introduced several refinements to Boussinesq’s hydraulic groundwater theory, allowing the inclusion of a capillary fringe, a seepage surface, leakage through the bottom, and slope.

“Infiltration theory is the area in which Jean-Yves Parlange has probably made the biggest impact. The essence of his approach consisted of replacing Richards’s equation by an integral representation, to obtain parsimonious yet remarkably accurate analytical approximations. Specifically, he represented several facets of partly-saturated flow by concise equations involving only sorptivity, saturated water content, conductivity, and water entry potential. The validity of these approximations was confirmed time and again numerically and with exact idealized solutions. It is no exaggeration that Parlange’s paradigm was one of the major breakthroughs in infiltration theory of the past three decades. The concept was made use of extensively by John Philip and his associates in Australia in their flux-concentration approach. Certainly, from my personal point of view, several of Parlange’s papers in this category have been seminal to my own thinking and have greatly affected my subsequent research in this field.

“Through it all, Jean-Yves Parlange has not only been a source of inspiration on the importance of fundamentals, but also a model of unselfish cooperation to be emulated by the rest of us. Most of his papers are co-authored, yet from personal experience I know that in most of them, with few exceptions, he was the intellectual leader and the main driving force.

“In summary, it is clear that Jean-Yves Parlange’s unwavering commitment in scholarship and teaching, coupled with his outstanding contributions in such a wide range of frontline topics, together with his generosity toward his colleagues, put him at the very top of our scientific enterprise. Unquestionably, there can hardly be a more deserving candidate for recognition through the Horton Medal.”

—WILFRIED H. BRUTSAERT, Cornell University, Ithaca, N.Y.


“President McNutt, Ladies and Gentlemen,

“Thank you very much Wilfried for your kind words and more than generous citation. It is, of course, a great honor to receive the Horton Medal especially considering the 17 previous recipients and I am extremely lucky to add my name to that list. I find it interesting that I know, to different degrees, more than half the scientists on it. I think it shows that hydrologists are a small close-knit community. It is also friendly and open-minded and I always felt welcome, even though I was never formally trained in that field.

“Wilfried gave the accurate account of my switch from aeronautical engineering to hydrology and I very quickly was encouraged by him as well as Don Kirkham and Don Nielsen, all Horton Medalists to pursue my research in hydrology. We always credit luck for our successes and indeed looking at our past it seems to be a random walk through life, but in fact we might be diffusing in response to gradients without even realizing it as individuals. However, and without any doubt, our main source of success is due to friends with whom we collaborate and who guide us without ulterior motives. I am deeply grateful to them. Several of them have been critical in determining the research paths I have explored. Among them are my Ph.D. advisor B. T. Chu whose teaching of mathematics and thermodynamics has had a profound influence and with whom I studied hydrodynamic stability; Calvin Rose and Bill Hogarth who introduced me to erosion and sediment transport, and Matt Romkens on the related topic of surface scaling; Peter Ross with his remarkable numerical skills; Larry Walker and his students who initiated me to biological engineering; Wilfried Brutsaert who is forever providing me with new ideas on all kinds of topics from mathematical derivations to the study of aquifers; Randel Haverkamp and Carlos Fuentes on infiltration and the inverse problem; Tammo Steenhuis with whom I have the closest research relationship at present who has a marvelous physical intuition and carries out illuminating experiments.

“I have also been blessed with outstanding students (and nowadays sometimes their own students) with inquiring minds and boundless energy and with whom I never stopped collaborating; without them, my research efforts would have been greatly reduced: John Selker, Andrew Barry, David Lockington, Frank Stagnitti, Ling Li, Todd Walter, and my own son Marc. There are many others who are too numerous to mention and yet their help has always been crucial and deeply appreciated. This is reflected in joint publications and I am quite proud to have half as many different co-authors as I have publications. All this would not have been possible without my wife’s support and encouragement, I was very lucky there as well. Finally, I am deeply grateful to the American Geophysical Union and specifically to the members of the Horton Medal committee for choosing me as the 2002 recipient of this wonderful medal.”

—JEAN-YVES PARLANGE, Cornell University, Ithaca, N.Y.

Donald R. Nielsen was awarded the Robert E. Horton Medal at the AGU Spring Meeting Honors Ceremony, which was held May 31, 2001, in Boston, Massachusetts. The medal recognizes outstanding contributions to the geophysical aspects of hydrology.



“The Horton Medal is the highest honor a hydrologist may receive. Today we add another giant, Donald R. Nielsen, to this most impressive list of recipients.

“As Don’s career at the University of California, Davis, parallels my own life, I hereby provide a brief overview to bring into perspective his many achievements. By 1958, as I was a toddler, Don was appointed assistant professor of irrigation. Ten years later, as I struggled to learn algebra, Don was already a full professor of water science, having authored over 65 articles. By 1973, when I entered college, Don served as associate dean of research and his publications exceeded 100 papers. By 1980, when I came to the United States to study hydrology, he had already served as department chair and as director of the Kearney Foundation; and his publications surpassed 140. By 1986, when I met him when joining the faculty at Davis, Don’s exceptional stature had advanced him beyond the highest rank conferred to a professor. Today, as I have the honor to write these words and as I am in the midst of my own academic career, I am no less than humbled by Don’s continued achievements for, even though officially retired from the university, his contributions continue and his publications have exceeded 300. But substance is not measured by numbers alone, as these by themselves may just lead to chaos on one’s career.

“Don’s outstanding contributions to the geophysical aspects of hydrology are many. Particularly noteworthy are his innovative achievements in the understanding of chemical transport through soils and the quantification of spatial variability of subsurface materials. In the early 1960s, Don, together with Jim Biggar, initiated basic research work on solute transport through soils. Via a comprehensive set of controlled laboratory experiments, they studied materials under unsaturated conditions and their observations led to a miscible displacement theory that first used advective-diffusive concepts, in a manner that is now taken for granted in the literature. As research moved to the field scale in the 1970s, Don became interested in the spatial variability of soils and, together with Jim, he carried the first comprehensive study that demonstrated the highly heterogeneous and scale-dependent nature of soil hydraulic properties and solute transport characteristics. Such seminal work established new and lasting directions in subsurface hydrologic research. It unequivocally revealed the relevance of research at the field scale and triggered an active development, even to this day, of probabilistic solute transport models capable of capturing the observed log-normal statistics and able to bridge the scale gap, from the laboratory to the field. But Don Nielsen’s achievements extend beyond these fundamental topics in hydrology and also include fundamental advancements in the study of nitrogen pollution and soil management.

“Via the lectures, courses, and workshops he has given in more than 30 countries around the world, Don has inspired many. As remarked by Art Warrick, ‘He is one of the strongest and most extraordinary mentors I have experienced in my career; this in spite of the fact that he was never a formal instructor or even a member of the faculty where I studied or worked.’ Don’s uncompromising standards, coupled with his unusual passion, propelled him to serve on numerous boards and committees that have shaped the course of hydrology. Within the American Geophysical Union, he served as president of the Hydrology Section and as editor of Water Resources Research. As swift action has followed Don’s words, he has been one of the most eminent flag bearers of hydrology as a science, leading to the promotion and implementation of NRC’s Opportunities in Hydrologic Sciences. And all of these accomplishments have been achieved while raising a family of five with his beloved wife, Joanne.

“For his fundamental and pioneering work in hydrology, combined with his uncanny love for the profession, it is my honor to present the most deserving recipient of the 2001 Horton Medal, Donald R. Nielsen.”

—CARLOS E. PUENTE, University of California, Davis


“Thank you, Carlos, for your kind and most generous words. I am deeply appreciative of being one of those to receive the Horton Medal. Their achievements continue to inspire me. Some of them I knew personally and better than others.

“For example, Walter Langbein nurtured my interest in written scholarship about hydrology. He sparked my initial commitment to the first volume of Water Resources Research in 1965.

“I also acknowledge John Philip. He informed my colleagues at U.C. Davis that I was really not very talented in mathematics. Thanks to him, I made a special effort to improve my mathematical awareness, and eventually, my colleagues approved my tenure, but not on the basis of my mathemetical ability. Pete Eagleson gave me the opportunity to learn from others when he led the development of the NRC book, ‘Opportunities in Hydrologic Sciences.’

“My major professor in soil physics was Don Kirkham–he and his wife Betty stimulated Joanne and me to concentrate on science, education, and on the lives of others. Ignacio Rodrequez-Iturbe taught me to stretch my imagination-to dream while I attempted to explore hydrology and other facets of life. And Wilfried Brutsaert, a student at U.C. Davis where I was a newly-appointed faculty member 40 years ago, helped me recognize the tremendous academic contributions made by students in addition to those expected of faculty members, scientists, and engineers.

“I am grateful to Wallace H. Fuller, who served as my M.S. advisor in soil microbiology at the University of Arizona. Through his advice, I switched from chemistry to microbiology, and eventually to soil physics with Don Kirkham. And after that, on my arrival at U.C. Davis, I was indeed fortunate to meet Jim Biggar–a colleague and friend who contributed as a partner to virtually every study I have made during my career.

“Having started my studies in agricultural sciences, I was challenged and helped by my colleagues in AGU to continue to learn and to explore uncharted avenues of hydrology. I especially thank Steve Burges–he remains my most valued mentor in AGU. I also wish to acknowledge the superb resources and academic environment of the University of California during my career.

“I was always blessed with bright students from many reaches of the world, eager to explore approaches to soil hydrology that I had yet to contemplate. I am indebted to each of them for advancing knowledge in soil hydrology, and now appreciate them as close friends and honored colleagues. Wilfried Brutsaert was correct: students were and continue to be the life of any scientific discipline.

“A very special acknowledgment goes to my wife Joanne, for without her support, I would not be here this evening. She is also the one who writes personal letters each and every day to previous students and colleagues throughout the world.

“Indeed, I am pleased to accept this wonderful medal. For me, it is a tribute for all of my colleagues who contributed their help and knowledge to improve my understanding of the vadose zone.”

—DONALD R. NIELSEN, Davis, Calif.

M. Gordon Wolman was awarded the Robert E. Horton Medal at the AGU Spring Meeting Honors Ceremony, which was held on June 2, 2000, in Washington, D.C. The medal recognizes outstanding contributions to the geophysical aspects of hydrology.



“Brilliant minds are not unusual among scientists. More uncommon are those who combine scientific acumen with a keen appreciation for history and geography, giving their work context in time and place. Rarest of all are those who can convey these gifts with humor, common sense, generosity, and style.

“Such a man is this year’s Horton Medalist, Professor M. Gordon Wolman, known far, wide, and hereafter as Reds. His career has left substantial legacies in hydrology and geomorphology as concepts, insights, publications, and, perhaps most important, students. He pioneered the first rigorous descriptions of natural streams and their beds and the first quantitative analysis of the relative effectiveness of geomorphic processes in shaping the landscape. He has given us new ways to think about the effects of land use, urbanization, and dams on channels and helped frame the international discussion on sustainable development.

“Reds comes by this medal honestly; his father, Abel, won it 14 years ago, making this the first father-son team to do so and adding the name of Wolman to other famous father-son teams: Bach, Einstein, and Ripken. Both father and son shared a fascination for water: clean in Abel’s case, dirty in Reds’. Reds began his career under the tutelage of some of this century’s greatest geomorphologists—Kirk Bryan, Luna Leopold, John Miller, and Walter Langbein, among others—and quickly became a part of what appears today as a golden age of fluvial geomorphology: the first attempt to rigorously and quantitatively describe the behavior of rivers.

“Singling out any particular work as Reds’ most influential is difficult. His 1953 paper on sampling particle size distribution of river beds led to the “Wolman pebble count” as a standard technique for geomorphology classes everywhere. His Brandywine Creek study is a classic example of a comprehensive geomorphic examination of a channel, presaging much of the contemporary interest in watershed analysis. His 1960 paper with John Miller and a follow-up in 1985 with Ran Gerson introduced the concept of evaluating geomorphic processes by integrating across the frequency distribution of effective events, providing much of the theoretical basis for modern process geomorphology. His 1967 paper on effects of urbanization on streams foreshadowed an entire subfield of hydrology. His 1978 paper with Gar Williams on downstream effects of dams is the standard reference for a global technical and policy debate. His papers in the last two decades span a wide range: fish spawning gravels, solid waste management, mountain stream organization, national water-quality trends, the relation between public policy and science, and, most fancifully, the role of play in science.

“No contribution better illustrates both his prescience and style than the 1964 classic “Fluvial Processes in Geomorphology,” by Leopold, Wolman, and Miller. Although written more than 35 years ago, it remains one of the most cited works in geomorphology and was recently republished by Dover, not as a historical artifact but as required reading for the newest generations of fluvial geomorphologists. Brimming with clarity and literacy (what other geologic text quotes Gertrude Stein on Niagra Falls?), it models how a textbook can be both scientifically authoritative and a good bedtime read.

“Arguably his most enduring legacy may be the generations of students he has taught over the years at Johns Hopkins. During the 1995 AGU Symposium in his honor, he was presented with an academic “family tree” that included 47 children, 106 grandchildren, 17 great-grandchildren, and four great-great-grandchildren. This tree continues to grow and branch, distinguished not only by the prominence of some of its members but also for the almost universal high regard and affection in which they hold their academic patriarch.

“I could go on and on citing Reds’ leadership role in professional societies and committees, etc., but I can hear him saying, ‘Please don’t.’ In his modesty, Reds seems genuinely surprised by the improbable course his life has taken. On a recent field trip down the Yangtze River, as the boat entered Wu Gorge with shafts of late afternoon sunlight illuminating an ancient temple on the flanks of Goddess Peak, Reds was heard musing, to no one in particular, ‘All this from counting pebbles!’

“Our community is indeed fortunate to count Reds Wolman among its elder statesmen—the Year 2000 Horton Medal could not be in finer hands.”

—GORDON GRANT, U. S. Forest Service, Corvallis, Oreg.


“The present is a propitious moment for hydrology, perhaps: a rare conjunction of interest in both the science of water and the management of water. The appearance of the science advisor to the President in a keynote speech on water at this AGU meeting is perhaps a manifestation of this special moment.

“Ancient, and some modern, civilizations in arid regions recognize the unique role of water in society. Today, the context is global. Moreover, the significance of water is recognized at what are often viewed as dichotomous poles in hydrology, science, and management. In one guise, water is a driving force in the dynamics of the atmosphere, a vital element in the creation of climate and of climate change. The management of water, seen as an increasingly scarce resource in many parts of the world, demands an understanding of the science of hydrology as well as the values, institutions, and machinery of social action. Both sides, the science of water and the management of water, capture today’s headlines. I believe this is a unique conjunction. This conjunction, of course, may or may not be propitious for funding. But, if it is, or will be, there are a few things we might try to do. Despite this heady platform, I do not have the capacity to list a priority of needs in the field of hydrology. I state here some biases, a few things perhaps worth focusing upon and a condition worth avoiding.

“Continued emphasis on the hydrologic cycle and on the role of water in models of the general circulation of the atmosphere on the globe remains of fundamental importance. Within that broad framework, the dynamics of the exchange of moisture between the litho-biosphere and the atmosphere remains a special challenge. For many water policy and management decisions, the oft repeated plea that finer spatial resolution is needed also remains true.

“As the sophistication of modeling at all scales increases, from the globe to the urban watershed, it has become evident that continuous, long-term records are essential both to hydrologic science and to water management. The need for long-term records exists in the United States, and the paucity of data in much of the developing world makes planning and design of water management systems, including the allocation of scarce water, much more uncertain than it need be. Conceivably, statistical issues of stationarity or the distribution of extremes even with long records, in the absence of some geophysical explanations of the driving mechanisms, may only be resolved in operational terms as allowances for risk, but the nature of the record is vital to the notion of adaptive management. Geologic reconstructions along with observation are needed to construct such records.

“In a concomitant vein, statistics alone are insufficient to understand the behavior of watersheds. Careful studies of processes responsible for the formation and transformation of the hydrograph, old-fashioned field studies in the eyes of some, remain essential to understanding the hydrology and to confidently translating this understanding into useful application.

“Institutions designed to manage water resources both depend upon and influence the kinds of hydrologic information collected and the way in which it is used. In the United States and in most nations, the many agencies of government are the dominant participants. No agency exists today at the federal level charged with the responsibility of rationalizing the diverse criteria and objectives of the many federal agencies with responsibility for different but interrelated facets of water management. Some inquiry into these institutional relationships may be warranted.

“These suggestions may be sufficiently broad to satisfy anyone’s taste in hydrology. I do not mean them to be, but more detail would be too much and inappropriate here. (What is appropriate here? Clearly, I don’t know.)

“While these calls for action are muted, almost a half century of exposure to the hydrologic scene suggests two features of the necessary debate over priorities in inquiry and research are to be avoided. I’ll call them rank and exclusivity. Rank may take the form of assertions of the superiority of theory over observations, of models over data, or of science over application. In principle, the general over the particular may indeed be more desirable. The same cannot be said, for example, for erroneous generalization or poor models. And, vice versa, bad observations even in the rain are not inherently better than some models. Exclusivity can be rank taken to the limit. However, no implication of rank per se is required. Thus there are enough data, models are useless, or watersheds not regions are the proper units of study. As the Eagleson committee makes clear, hydrology is inseparable from a host of processes encompassing the biosphere and lithosphere and the varied realms of water. Given that complexity, first-rate work from a vast variety of avenues is demanded. Of course, the rhetoric of rank and exclusivity is not unique to our fraternity. But we are a relatively small band needing common ground to be most effective.

“My citationist has been most generous. To those distinguished friends mentioned in the citation and to many others in the field, I owe my very good fortune. I am honored beyond measure to receive the Horton Medal from the American Geophysical Union.”

—M. GORDON WOLMAN, Johns Hopkins University, Baltimore, Md.

Wilfried H. Brutsaert was awarded the 1999 Horton Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 15, 1999, in San Francisco, California. The Horton Medal is given for outstanding contributions to geophysical aspects of hydrology.



“The Horton Medal is for ‘outstanding contributions to geophysical aspects of hydrology.’ By any measure chosen, Wilf Brutsaert is most deserving of this honor.

“I first met Wilf in 1981 when we worked together on the editorial board of Water Resources Research. I quickly came to value his wise counsel and friendship and the depth and breadth of his scholarship. He is extremely generous with his time for family, friends, students, and colleagues. He provides intellectual leadership to the community through his personal scholarship and collaborations. He brings the enthusiasm of the brightest and most energetic, recently graduated Ph.D. to all that he does. His decades of leadership within AGU and in numerous activities that have yielded scientific opportunities for many have been absolutely selfless.

“Wilf has investigated primarily the fluid mechanics of environmental phenomena to solve critical problems of hydrology. His research constitutes a perfect balance of theory with careful and appropriate experiments. He has published pioneering and lasting papers on vadose-zone and hillslope hydrology, gas exchange at air-water interfaces, and aquifer dynamics. He is best known, however, for his original and incisive contributions in the description of the transport of vapor through the Earth-atmosphere boundary layer and has been at the forefront of establishing programs that make the best use of both groundbased and remote platform measurements to quantify evapotranspiration. As an example of his influence, authors now refer to one of his similarity schemes as the ‘Penman-Brutsaert’ approach.

“Wilf writes beautifully, never overstating the case, and always places the situation into perspective. There are several examples that highlight the breadth and depth of his work on evapotranspiration. His 1976 paper with Mawdsley, The application of planetary boundary layer theory to calculate regional evaporation, revolutionized the use of atmospheric boundary layer fluid mechanics to estimate regional evapotranspiration. His 1986 paper, Catchment scale evaporation and the atmospheric boundary layer, provided the foundation for the direction of significant ongoing research by many colleagues. The 1992 paper with Sugita, Landsat surface temperatures and radiosoundings to obtain regional surface fluxes, and the 1996 paper written with Qualls, Evaluation of spatially distributed ground-based and remotely sensed data to estimate spatially distributed sensible heat fluxes, demonstrate his penchant for tackling ‘wicked,’ real-world problems. His 1998 Nature paper with Marc Parlange on the Evaporation Paradox resolves a thorny problem in hydrology and a key issue in the current global change debate.

“Wilf cares deeply about and makes the considerable effort to research the history of our field. An example is from his 1992 AMS Horton Lecture, Horton, pipe hydraulics and the atmospheric boundary layer (Bulletin of the American Meteorological Society, June 1993) in which he traced the theoretical developments of the atmospheric boundary layer methods used to estimate vapor transport from large land areas. He identified the critical measurements supporting the early theoretical developments of Blasius and Prandtl as those conducted in 1902-1903 at the Hydraulics Laboratory at Cornell University, Wilf’s academic home, to determine resistance to water flow in pipes. (Robert Horton worked with the research staff, Saph and Schoder, soon after they completed this work.) Before Wilf’s lecture, few knew about the early fundamental measurements underpinning this theory.

“Marc Parlange summed up Wilf’s work: ‘He has done it all in hydrology. He has carried out brilliant research in numerical and analytical methods for partial differential equations describing environmental transport, he has collected precious laboratory and field measurements which remain benchmarks for theoretical comparisons, and he has developed foundational theories for the description of regional hydrology and land-atmosphere vapor exchange. No physical hydrologist has ever touched so many areas in such depth.’ Kuo-Nan Liou commented that Wilf’s 1982 book on evaporation into the atmosphere ‘has been and is still considered by many scientists in atmospheric and hydrological disciplines to have provided the physical foundation for the connection of the land surface and atmospheric boundary layer.’ Jeff Dozier observed that this ‘is the best reference book on my shelf.’

“Wilf Brutsaert embodies all that is good about AGU, is the complete academic scholar-teacher and research scientific leader, and exemplifies ‘unselfish cooperation in research.’ President Knauss, ladies and gentlemen, it is a privilege and honor to present my friend and colleague, the winner of the 1999 Horton Medal, Wilfried Brutsaert.”

—STEVEN J. BURGES, University of Washington, Seattle


“Thank you, Steve, for your generous citation.

“Mr. President, ladies, and gentlemen, despite what Steve Burges has just been trying to tell you, the reality is that I have somehow had the good fortunes of being at the right place at the right time and of meeting the right people at different junctures in my life.

“Certainly, it was nothing but a coincidence and mostly sheer luck that when I arrived on a freighter and first set foot on this continent as a fresh graduate to hitchhike my way from New York to California, Sputnik had just been launched. This event, in the middle of the Cold War, would eventually lead to what was probably one of the largest expansions and hiring sprees in the history of higher education in this country. Of course, I had no way of knowing then that I would end up in a life of research and teaching and that it would eventually come to this.

“I was also unbelievably fortunate in being able to interact with several outstanding individuals, and there is no question that whatever this medal holds or reflects, the merits are as much theirs as they are mine. As early as my undergraduate years in Ghent, it was a stroke of good luck that I was exposed to the mathematical discipline of Gerard Heyndrickx and to the straightforward charisma of Don Kirkham, which made me decide to go on to graduate school. It was Kirkham who then steered me to one of his former graduate students, Jim Luthin, at the University of California at Davis, which at that time was one of only a handful of institutions where hydrology was being approached in a comprehensive and fundamental way. At Davis, Don Nielsen’s analytical and experimental insights exerted a lasting influence on my thinking. And after I came to Cornell, my almost daily interactions with Jim Liggett, Gerhard Jirka, and, more recently, Jean-Yves Parlange were invaluable and stimulating. Among the other colleagues who were a source of inspiration and motivation over the years, I have to mention Giichi Yamamoto at Tohoku-Dai in Sendai, Dirk Kraijenhoff van de Leur at Wageningen, Herbert Lang at the ETH in Zurich, Peter Eagleson at MIT, Francois De Troch at Ghent, and Kuo-Nan Liou at UCLA. In addition, over the years I have been blessed by a steady stream of graduate students. They are too numerous for me to thank them by name here and now, but they know who they are. Let me just say that to work with them has been one of my life’s greatest pleasures. Finally, I would have liked to recognize my wife, Toyo, my close companion and friend for the past three decades. But I know she doesn’t want me to talk about that….

“In closing, I want to express my gratitude to AGU for bringing us all together here in this spirit of fellowship and cooperation and to the members of the Horton Medal Committee for their trust and confidence.”

—WILFRIED H. BRUTSAERT, Cornell University, Ithaca, N.Y.

Ignacio Rodriguez-Iturbe was awarded the Robert E. Horton Medal at the AGU Spring Meeting Honors Ceremony, which was held on May 27, 1998, in Boston, Massachusetts. The Robert E. Horton Medal recognizes outstanding contributions to the geophysical aspects of hydrology.



“The Horton Medal is the highest honor bestowed upon hydrologists. Indeed the list of past winners is very impressive. In the words of my colleague, Pete Eagleson, ‘today we add the foremost surface water hydrologist.’ I fully concur.

“Ignacio Rodriguez-lturbe has been a major player in, if not originator of, some of the most significant hydrologic breakthroughs in the last 30 years. Allow me to sketch an extraordinary time line.

“In late 1960s and early 1970s, he clarified the debate on the occurrence and persistence of hydrologic extremes, commonly known as the Hurst phenomenon. He formulated one of the first self-similar models to simulate extreme behavior.

“In early 1970s, he framed the whole issue of monitoring network design as one of sampling of random fields. For the first time the art became a science.

“In mid-1970s, he introduced Bayesian approaches to estimate parameters of streamflow simulating models and to select models of extremes. The profession suddenly had a consistent way to use regional information to predict extreme hydrologic behavior in regions with limited data.

“In the late 1970s and early 1980s, he re-energized the field of fluvial geomorphology with a fresh look at basin organization and its relation to basin response. He developed the Geomorphologic Instantaneous Unit Hydrograph (GIUH), the most successful attempt to quantify the discharge of a basin as a function of basin geometry and rainfall.

“He has led the revolution in fluvial geomorphology from the late 1980s to the present by developing a whole new theory of river basin organization and evolution. The new theory has shown that organization of the basin and resulting landscape patterns are not the result of randomness but process-driven phenomena that can be quantified in terms of well-defined principles.

“During the 1980s and 1990s, Ignacio also spearheaded the use of point processes and fields to represent precipitation in space and time. We now have virtual realities that facilitate forecasting and analysis in hydrometeorology.

“Since the late 1980s, he also showed the impact that simple nonlinearities in the land-atmosphere dynamics have on patterns of hydrologic variables, like soil moisture. Droughts, for example, may be enhanced by the complicated feedbacks between the land and the atmosphere.

“This record is sufficient for many careers. However, let me assure you, he is not finished! He is now immersed in biology, seeking new inspiration to solve problems in hydrology.

“Professor Donald Nielsen captured the essence of this scientist when he wrote: ‘To be in the same room with Ignacio is an inspirational experience. He brings the wisdom of the past, the direction of the present, and the uncharted, yet to be conceived, approaches of the future into full view. He challenges each of us to the depths of our understandings, and at the same time encourages risk, excitement, and scientific reward. I know of no other contemporary hydrologist who lives each day inspiring those inside and outside of hydrologic science more than does Ignacio.’

“That ebullience and contagious enthusiasm has propelled many of his students to very successful careers. I am proud to be one of them.

“Merely to know Ignacio’s science is to miss his most important quality, his humanity. Ignacio is a man of impeccable honesty, of deeply rooted principles, and of uncompromising devotion and loyalty. All this packaged in a hyperactive body and mind, full of humor and zest for life. He is the friend, the confidant, and the inseparable companion of his wife, Mercedes. He is the loving beacon to his five children: Oscar, Ignacio, Olympia, Juan, and Luis. To his friends, he is the reliable counselor who is always present when needed and is also the bearer of good cheer. I look forward to our weekly telephone conversations.

“President Solomon, ladies and gentlemen, it is an honor to introduce my mentor, friend, and brother. As a colleague put it, the ‘Paganini of Hydrology’–the winner of the Horton Medal–Ignacio Rodriguez-lturbe.”

—RAFAEL L. BRAS, Massachusetts Institute of Technology, Cambridge, Mass.


“President Solomon, ladies and gentlemen:

“Thank you, Rafael, for your most generous words. It is like a dream for me to receive the Horton Medal and even more so to receive it in Boston, a city so special for all my family. I have been extremely lucky to be a hydrologist during a time that has seen the field transformed from an appendix of hydraulics, -full of empirical formulas and driven by the requests of engineering practice, to a science of its own, motivated by the desire to understand how nature works that, as a consequence, brings the capability to solve. The fact that hydrology was ready to undergo a dramatic transformation was made clear to me by my undergraduate advisor in Venezuela, Jan Laszewsky. This was reinforced when I joined the hydrology program at Colorado State University, where hydrology was pursued and argued at every moment of the day. It was a marvelous time and the right place to be, with people like Jose Mejia, David Dawdy, Vijay Gupta, and Carl Nordin under the leadership of Vujica Yevjevich.

“My first paper submitted to AGU was sent in 1968 to Water Resources Research from Universidad del Zulia, handwritten with a letter explaining that to have it typed in English would take a long time and certainly would not improve its appearance! The editor was Walter Langbein, the first Horton medalist and a giant of the field. He read the manuscript and answered me in a handwritten letter that the paper would be reviewed, and if accepted, he would take care of the typing. I will always be grateful for this kind and generous answer to a very young and unknown hydrologist trying to do research under difficult circumstances. In early 1970, I received an invitation from Peter Eagleson to join the faculty at the Massachusetts Institute of Technology. It was the beginning of many personal and professional friendships that will last a lifetime, regardless of where we have been or where we will ever be.

“Throughout my academic life, I have been blessed with wonderful students that became dear friends and admired colleagues. Three of them who shared an office at MIT during the early 1970s are here tonight with their wives: Rafael Bras, department head at MIT, Juan Valdes, department head at the University of Arizona, and Eric Wood, former department chairman at Princeton. Indeed, I was lucky with the students that came my way! To all of them, I can only say thanks for graciously putting up with a peculiar advisor who would telephone late at night to talk about research. It was exciting! We got involved in all kinds of research problems and would continuously discuss what we perceived as the key challenges of the field. I was extremely fortunate during those years at MIT to have two exceptional academicians, Donald Harleman and Peter Eagleson as mentors, both personally and professionally. Our families will always be very close and I owe them more than I can express with words.

“In Venezuela, Universidad Simon Bolivar was a wonderful place to work with friends like Jose Cordova, Marcelo Gonzalez, Luis Castro, and Luis Pericchi, who are still very dear to me. From there, and through the generosity of many friends from all over the world, I was able to pursue a variety of topics that had been on my mind for a long time. With Andrea Rinaldo, of the University of Padova, I have had many especially exciting years of research and friendship, and I thank him for sharing with me his enthusiasm and creativity. Dara Entekhabi of MIT has also been a wonderful research partner, although he keeps remembering that I once told him he was ‘an ocean of useless information.’

“Rafael Bras was a spectacular student and a wonderful research partner from the very first day he walked into my office. Most importantly, he has always been a very special and dear friend. When we left MIT to go back to Venezuela, I assured Pete Eagleson I would not be missed. I said this with all sincerity. Rafael had decided to return from Puerto Rico to join the faculty, and I had no doubts whatsoever that he would quickly become a world leader in the field. Throughout the years, we have collaborated in many projects and, as time goes by, I feel more and more proud of his many accomplishments.

“Pete Eagleson, former president of AGU and the 1988 Horton medalist, has been my mentor, a most admired colleague, and true family, both in the good times and in the tough times. His work has been an inspiration for all of us since the 1960s, and we continuously share the excitement of research as well as the ups and downs of life. His friendship and trust acquire a deeper meaning as the years pass.

“I am forever thankful to AGU, which has been a most important institution in all my scientific endeavors regardless of where in the world I was living. Since 1993, Texas A&M University has provided a supportive environment for all of my activities, and I am especially grateful to Bud Peterson, our Associate Dean of Engineering.

“Finally, I want to thank my family. I always tell my students that to do good research it is necessary to be able to dream. If I have any capacity to dream I owe it to my father, who until the end of his life, after being blind for years, would repeat that to see far and to see well one needs the eyes of the heart. The eyes of my heart have always been on Mercedes and our children, from whom I have learned, day after day, the meaning of love and generosity. As we say in Spanish, amor con amor se paga.’ Thirty-five years ago, my senior thesis in Maracaibo started with the words, to Mercedes with love and dreams.’ Tonight this wonderful medal is for her, with the same love and the same dreams of 35 years ago.”

—IGNACIO RODRIGUEZ-ITURBE, Texas A&M University, College Station

John Bredehoeft was awarded the Robert E. Horton Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 10, 1997, in San Francisco, California, USA. The Robert E. Horton Medal recognizes an outstanding contribution to the geophysical aspects of hydrology.



“John D. Bredehoeft has been awarded the Robert E. Horton Medal for outstanding contributions to the geophysical aspects of hydrology. That this is well deserved is beyond question. Befitting the purpose of this award, I begin by noting that John is among the few whose contributions to hydrology include several that are also noteworthy in the realm of classical geophysics. How many hydrologists do we know who were involved not only in studying but also in creating earthquakes? John did this as a participant in the well-known Rangely, Colorado, experiments (where earthquakes were created and controlled by high-pressure fluid injection). He followed up on this by contributing to the Parkfield, California, earthquake studies, where he was a proponent of using water wells as strain meters to monitor Earth deformation near faults, partly in search of potential earthquake precursors. It is difficult to envision a stronger link between geophysics and hydrology than these two examples.

“However, John has done so much more, and of course the Horton Medal is not predicated just on research as a geophysicist, per se. John is recognized internationally as a pioneer in the study of groundwater flow systems.

“Among the aspects that characterize John’s work is his multidisciplinary approach to solving difficult problems. He has made important advances linking groundwater hydrology with geophysics, geochemistry, tectonics, petroleum engineering, economics, and numerical methods. Another characteristic of John’s contributions is his ability to relate and link theoretical advances to field problems. He has developed many practical tools and methods in use today on the basis of sophisticated and complex technical analyses. Conversely, many of his contributions to basic theoretical scientific advances have evolved from his identification of particularly difficult and vexing field problems. John’s extraordinary talents and contributions have great breadth and depth, since they extend beyond the purely technical realm of science and engineering into the less-concrete realms of the management of natural resources, the management and administration of research organizations, and even the philosophy of science.

“A common thread running through much of John’s work is his interest in the role of fluids in geologic processes. John’s first publication, in 1963, was the first quantitative examination of membrane filtration in the subsurface. His 1967 paper on the response of aquifers to Earth tides is extensively cited as the seminal paper on that topic. His 1968 papers on anomalous fluid pressure were the first cogent analyses of geologic processes as hydrologic driving forces and the first recognition of anomalous pressures as hydrodynamic transients. His analysis of thermal profiles for estimating groundwater flow rates is elegantly simple, yet has proven to be of tremendous utility. He was among the first to use hydraulic fracturing as a method for determining the state of stress in the subsurface. Thirty years ago, many geologists barely recognized the existence, let alone the importance, of subsurface fluids. That is no longer true today, and geologists in great numbers are now looking at how groundwater controls or influences ore deposits, hydrocarbon reservoirs, tectonic processes, volcanic events, and almost every other subfield of geological and geophysical sciences.

“In the realm of groundwater systems analysis, John has made several fundamental contributions to methods of well test analysis. His 1965 paper on drill stem tests helped make available a huge amount of subsurface permeability data in the petroleum industry that had not been previously tapped by hydrologists. He was also instrumental in the development of the rigorous theory of slug tests, now one of the basic tools of the field hydrogeologist that is used with increasing frequency in the study of subsurface contamination sites. Finally, he extended the slug test technique to solve the difficult problem of field measurement of very low permeabilities.

“Most practicing hydrogeologists today routinely apply computer simulation models to help them understand and solve the particular problem being addressed. They all owe a debt of gratitude to John Bredehoeft, who helped pioneer the development and application of digital simulation of groundwater systems when most hydrologists were still using analog models. His papers, particularly those coauthored with George Pinder, are widely recognized as standard references in groundwater model analysis. Many model developers built upon the basics that John laid out, and many of today’s flow and transport modelers use programs based on his work. In the early 1970s, John was among the few who saw the significance and pervasiveness of groundwater contamination problems: this was a motivating factor for his development and application of solute-transport models. Less than 20 years later, dealing with groundwater contamination has become a multibillion dollar a year industry, probably exceeding even John’s usually accurate foresight about wide-reaching issues.

“Regional groundwater flow has been another persistent theme in John’s research. His work on geological membranes marked the first rational explanation of the Illinois Basin’s distinctive brine pattern in terms of regional flow. His later innovative analysis of the Dakota artesian aquifer system showed how shale confining layers mediated aquifer behavior. He demonstrated for the first time the tempering effects of water storage in shale and obtained the first regional permeability values for tight shales.

“John has been a thoughtful and influential critic of the nation’s research initiative for disposal of nuclear wastes. He coauthored the U.S. Geological Survey (USGS) position paper on this subject in 1978. John also challenged prevailing views of the impermeability of salt at the WIPP site in New Mexico (designed for storing transuranic wastes in salt beds) and postulated the consequences of Darcian flow through the salt on the repository’s integrity. This paper significantly altered the course of action of Department of Energy contractors. A few years ago, John was also asked to evaluate a major criticism of the proposed high-level nuclear waste repository at Yucca Mountain in Nevada. His efforts helped to resolve the issue of whether seismic activity there could raise water levels enough to flood the repository (which it would not).

“Most scientists get sufficient satisfaction from seeing their research results published and recognized by their peers. John strives for more, and he recognizes a need for society to benefit from the research that taxes are supporting. His interest in promoting a `practical payoff’ of science is illustrated in the area of groundwater management, where the papers of Bredehoeft and Young represent pioneering work. He showed how economic theories can be applied in light of realistically variable hydrogeologic conditions to develop policies for water allocation or development of groundwater resources. In subsequent papers, John analyzed topics such as groundwater depletion, conjunctive use, and artificial recharge. Among other things, he demonstrated the fallacy of basing groundwater management rules (such as restrictions on pumpage) on computed water budgets (or recharge rates) for conditions prevailing prior to development.

“John is not only a leading scientist, but a leader of scientists. John served for many years as Chief of the National Research Program of the Water Resources Division (WRD) of the USGS, which at that time employed close to 300 scientists and engineers. In this position, John substantially increased the relevance and visibility of this hydrologic research program. He later served for several years as Regional Hydrologist for the operational program in the eight-state Western Region of WRD. His successful efforts to create a `research-in-the-District’ program has led to the better balance between scientific investigations and data collection throughout WRD that exists at the present time. Perhaps the most amazing feat is that John remained a productive scientist and researcher during the years he served as a manager.

“In summary, it is clear that John Bredehoeft’s scientific talent, productivity, and leadership in groundwater and related fields have made outstanding contributions to the geophysical aspects of hydrology. These contributions attest to John’s stature as a leading thinker on water-related issues of scientific and social importance. John’s advice on problems of national and international concern is valued: he has served on numerous panels and committees dealing with a wide range of water-related issues. Many of his personal research achievements rank as milestones of modern hydrology and have served as the basis for the work of others in the field. His creativity and originality of thought, his insight and ability to identify the most critical and worthwhile problems of the day, and his generous support and encouragement of young scientists combine to make him a role model for others to emulate.

“John, I speak for your many colleagues, and your former students, in stating that we strongly believe that your numerous scientific achievements, scientific contributions, and scientific spirit (most notably encompassing your strong support for students and young scientists), have made you most deserving of this prestigious Robert E. Horton Medal. Congratulations!”

—LEONARD F. KONIKOW, U.S. Geological Survey, Reston, Virginia


“I am pleased to join a number of distinguished hydrologists in receiving the Horton Medal. I have been fortunate to know most of them personally.

“As Allan Freeze pointed out upon receiving the M. King Hubbert Award, luck plays a part in all our careers. I was lucky to go to the University of Illinois, where my major professor and mentor was Burke Maxey. He instilled in those of us who were associated with him a demand for excellence. Upon receiving my Ph.D. in the early 1960s, I was lucky to go to work at the U.S. Geological Survey. I arrived at a time when I could apprentice with some of the best professionals engaged in the study of groundwater. It was with Bob Bennett, Hilton Cooper, C.V. Theis, Bob Stallman, Herb Skibitski, Jacob Rubin, and Walter Langbein that I was able to learn my profession. These individuals built much of groundwater science as we know it today. Many young people do not have the opportunity to apprentice with a group of senior mentors as I did at the USGS. I owe my maturity as a scientist to them.

“The USGS gave me the opportunity to pursue my research more or less unfettered. Like any successful individual, I paid my dues both in doing research that furthered the everyday missions of the Water Resources Division and, in the tradition of the USGS, doing my stints of administration. I had opportunities to leave, but each time I evaluated leaving I came to the conclusion that the USGS afforded the best opportunity to do the research that interested me. I left the Survey in 1994 to do something different during the rest of my life: to build a consulting business. That too has been fun.

“My research involved the investigation of various facets of fluids in the subsurface. I have moved around from topic to topic in my research, always with the focus on fluids in the subsurface. It always seemed there was more to learn: that was the fun in this endeavor. The USGS afforded the freedom to pursue my interests.

“One does make major contributions in any of life’s endeavors with the support of your family. My family has been most supportive, especially my wife, Nancy. I would especially like to thank Nancy.

“I am pleased to accept the Horton Medal for myself, as well as my colleagues in research in the Water Resources Division at the USGS, and especially my other colleagues who study fluids in the Earth. The award to me recognizes all of us.”

—JOHN D. BREDEHOEFT, The Hydrodynamics Group, La Honda, Calif.

Mark F. Meier received the Robert E. Horton Medal on December 17, 1996, at the AGU Fall Meeting Honor Ceremony in San Francisco, Calif. The Horton Medal acknowledges outstanding contributions to the geophysical aspects of hydrology. The award citation and Meier’s response are given here.



“The Horton Medal is awarded in recognition of `outstanding contributions to the geophysical aspects of hydrology.’ For the first time, this medal will be presented to a hydrologist who has concentrated his attention on water in its solid phase. Mark F. Meier’s long and distinguished career in glaciology spans most of the modern era for that science, and he himself has played a central role in leading glaciology from its historical domain as a self-marginalized hobby of amateurs and adventurers to its present status as a fully mature geophysical science. Mark has helped steer glaciology to this high ground both by the example of his science and by his outstanding leadership of key scientific organizations.

“Like many who share the blessing of an Iowa birthplace, Mark acquired a profound love for the mountains and the sea. Important figures in his early scientific development were his father, a professor of psychology and a geology enthusiast; Robert Sharp, supervisor of his Caltech doctorate on glacier flow mechanics, Friedl Hoinkes, an Austrian expert on glacier energy and mass balance measurements, and Luna Leopold, who invited Mark to found a glaciological research program within the Water Resources Division of the U.S. Geological Survey.

Mark took up this offer, and in 1956 was appointed Chief of the USGS Project Office – Glaciology in Tacoma, Washington. As a glaciologist working within the Water Resources Division, he was quick to grasp the Cartesian dualism that described his situation: glaciers melt, therefore they are a water resource. During his 30-year tenure as a project chief, he assembled a remarkably talented and heterogeneous group to conduct fundamental research on the hydrological aspects of glaciers and snow. Accomplishments of Mark and his Tacoma colleagues include the establishment of a rational framework for mass and water balance data collection and demonstrations of the value of such measurements in monitoring climate change. Traditionally, mass balance studies have been seen as necessary but mundane. By a combination of rigor and high-mindedness, Mark has played a unique role in rehabilitating this area of glaciology: first, by clearly articulating why such measurements should be taken, and second, by demonstrating how such a measurement program should be conducted.

“Among scientists concerned with glaciers, Mark has been the one most prominent in relating glacier processes to wider concerns in hydrology and environmental science. In his later years at USGS, he expanded his research on the mass balance of mountain glaciers to address the question of how glaciers affect global sea level. His 1984 paper in Science on this topic is vintage Meier. It gives motivation and honorable purpose to an area of glaciology that is sometimes disparaged: it steadfastly focuses on the big picture and it links the comparatively small scale and small issues of glacier processes and responses to the giant scale of the Earth system and urgent issues of global change.

“Perhaps the most memorable work to emerge from the USGS years came from Mark’s enormously fruitful collaborations with Austin Post. Together they highlighted the importance of fast glacier flow and glacier flow instabilities. Their classic 1969 paper entitled “What are glacier surges?” presented such a definitive description of the phenomenon of surging and such a clear statement of the associated challenges to science that it has served as a virtual battle plan for all subsequent research on that subject.

“The culmination of Mark’s years with the USGS was the Columbia Glacier Project. Pursuing their interests in flow instability, Meier and Post drew attention to a potential instability associated with flotation and the rapid disintegration of tidewater glaciers and pointed to a likely candidate, Columbia Glacier, on the Alaska Coast. Furthermore, they noted that the present state of the glacier was near the trigger threshold and warned that rapid disintegration and catastrophic retreat of the lower Columbia Glacier would disgorge icebergs into Prince William Sound, the now-famous maritime route followed by such vessels as the Exxon Valdez. As chief of the Project Office-Glaciology, Mark was able to convince his USGS superiors of the scientific interest and possible danger of this unusual environmental hazard. In doing so, he succeeded in launching what was unquestionably the first and only example of “big science” applied to a nonpolar ice mass. I doubt if anyone else could have formulated the scientific plan or marshaled the resources that brought the project to life. Now, however, the pressure was really on. If the instability failed to develop, a deeply embarrassing situation would present itself. Nature is rarely cooperative when scientific reputations are at stake, but Columbia Glacier proved the exception; the glacier began its catastrophic retreat on schedule, and the retreat itself spawned excellent science on iceberg calving and the subglacial hydrology of fast-flowing glaciers. “Like his research contributions, Mark’s leadership and service contributions are so numerous and wide-ranging that they can only be touched upon. A consistent thread is that Mark never accepts a job without leaving his imprint. It is not the status that attracts him, but the opportunity of using the instruments of leadership to achieve a worthy objective. As president of the International Commission on Snow and Ice (ICSI) during the International Hydrological Decade, he seized the opportunity to promote glaciology as a hydrological science by launching the international Combined Heat-, Ice- and Water-Balances Program, the World Glacier Inventory Program, and the Permanent Service on the Fluctuations of Glaciers. As the first glaciologist to become President of the International Association of Hydrological Sciences, he worked to improve the integration of ICSI within the Association and to enhance the visibility and acceptance of hydrology within the geophysical sciences. In 1985, Mark left the USGS to become director of the Institute of Arctic and Alpine Research at the University of Colorado, Boulder. In that capacity he molded the Institute into a thriving endeavor, with greatly increased financial support and a high international reputation. As a member of the first U.S. national committee to define a geosphere-biosphere program, he participated in shaping the national and international Global Change Program and led the development of an arctic global change program.

” Mark Meier’s colleagues regard him as a kind of navigator for the science of glaciology because he has always been able to locate the high road and lead others toward it. We speak of him as the ‘Wise Man of Glaciology’ (interestingly, not the Wise Old Man, because none of us think of him as anything but an active scientist). His gift for enunciating clear and compelling paradigms has helped make him one of the most influential glaciologists of our time. His enduring legacy is to have shaped the future of a science. By leadership and example, he has encouraged glaciology to shed its parochialism and to raise its stature as a geophysical science. In doing so, he has helped the scientific community appreciate that glaciology is a key component of the hydrological sciences and that the cryosphere is an important wild card in any discussions of global change. Mark, there is no glaciologist more deserving of the Horton Medal. Your colleagues celebrate this achievement with you.”

—GARRY CLARKE, University of British Columbia, Vancouver, B.C.


“I am greatly honored to be this year’s recipient of the Robert E. Horton Medal, and am especially pleased to have Garry Clarke present the citation. I have long admired Garry’s intellectual depth: his many seminal contributions in the field of glacier dynamics, his breadth of productivity in geophysics, and his ability to stimulate students and colleagues with great ideas. We have worked together quite a lot in research and in scientific ventures, as well as in that wonderful nonorganization called Northwest Glaciologists; he is certainly one of my heroes.

“It is also a great honor to be connected with Robert E. Horton, who established the foundation for quantitative drainage-basin analysis. As a graduate student, many years ago, I tried to contribute to this field. I normalized and aggregated lots of area-altitude data and found, to my surprise, that the results showed what we would now call self-similarity as well as a stochastic distribution. Although my own attempts did not succeed very well, it is gratifying that the ideas were picked up later by others and are part of the major revolution in geomorphic analysis begun by Horton.

“I am lucky to have been able to pursue a career in glaciology. Glaciology is a fun and exciting field of science. It takes one to beautiful areas of the world, it exposes one to both intellectual and physical challenges, it provides special insight through the observation of solid Earth processes in motion, and it has significant ramifications to many other environmental, solid Earth, and fluid Earth sciences. Because of the unusual work areas, the need to share responsibility for each other’s safety in the field, and the fact that it is a rather small scientific discipline, there is wonderful camaraderie and personal friendship among its practitioners. If I were starting a new life in science, I think I would again choose glaciology – although there have been a few times, when my feet were cold, my sleeping bag was wet, and my instruments were suffering from both cold and wet, that the fields of volcanology or coral reef ecology sounded very attractive. Glaciology is inherently interdisciplinary, and many of my colleagues are also talented in other sciences and even in the arts; they are an exciting and interesting bunch to be with.

“I have to mention that during the years of my career there were enormous gains in the research toolbox. Early on, I thought that the major breakthrough in glaciological instrumentation were Write-in-the-Rain notebook paper and the aluminum grain scoop. We measured glacier velocities, for instance, by reading verniers on heavy transits and laboriously reducing the data after leaving the field, using glorified adding machines and books of interpolated trigonometry functions. Now we use automated electronic distance measurement instruments or GPS positioning or measure velocity fields by synthetic aperture radar interferometry from satellites. Scaling and other mathematical techniques from the emerging field of complexity are making it possible to find structure in complicated data sets, so that conclusions can be drawn even though the physical processes are poorly understood. These are remarkable changes, and they have transformed the field significantly. What will we be able to do in another few decades? I hope that the young researchers of today realize how rapidly new opportunities are being created! The specifics of these new methods cannot now be imagined, but the next generation of researchers should be preparing for them by obtaining broad background in mathematics and the basic sciences and watching progress in neighboring disciplines.

“Many of us who have attained honors such as this one have done so by riding on the shoulders of giants, and this is especially true with me. I would first like to thank my teacher, Bob Sharp, and the challenging intellectual atmosphere at Caltech. I will never forget Bob’s repeated question, after I had reported someone’s result, “How do YOU know?” I also owe special gratitude to the late Friedl Hoinkes, who taught me the physics of energy balance measurement as well as how to work with scientists of very different values and agendas, and to Luna Leopold, who created a broad and productive hydrologic science machine within the Water Resources Division of the Geological Survey and hired me into it. I wish that I could publicly list and thank the many colleagues and coauthors who have contributed in large part to any success I might claim, and it hurts me to be unable to do this. A few who had an inordinate contribution to my productivity include Austin Post, who has the best intuitive and observational grasp of glaciology in action of anyone I have ever met and who is incredibly quick to perceive the heart of an unusual problem or behavior; Al Rasmussen, who is always full of ideas on how to solve seemingly intractable problems and who cleaned up my sloppy mathematics; and Bob Krimmel, who produces first-class data year after year in sometimes trying circumstances. At the University of Colorado I have been working especially with Tad Pfeffer on a new array of glaciological programs, and David Bahr, one of my first Ph.D. students, who introduced me to the usefulness of nonlinear mathematics.

“In the citation, Garry mentioned that I am the first glaciologist to attain this medal, and he also alluded to a “Cartesian dualism” regarding solid- and liquid-water hydrology. I would prefer to look at this rather differently: the partitions dividing the disciplines may be necessary for science management, but as is emphasized in the Global Change Program, the physical and biologic processes in the Earth system do not recognize these partitions. One can often find fruitful new opportunities in research by moving out of one’s designated area. This brings me to another acknowledgment: I wish to thank AGU publicly, not only for granting me this important award, but more importantly, for creating an interdisciplinary atmosphere at meetings where the boundaries between disciplines can be explored easily. This interdisciplinary ‘melting pot’ atmosphere is, in my mind, a most exciting aspect of an AGU meeting; it allows us to garner ideas or learn of techniques in neighboring disciplines for application to one’s own work. I am certainly indebted to AGU for creating this stimulating environment. If there is one message that I most wish to convey to the younger scientist, it is to stay broadly focused and keep your eyes on, and beyond, the borders of your discipline – that’s where the excitement is!

“Finally, but most importantly, I wish to direct special thanks to my wife, Barbara, and my family, for loving and supporting me in spite of my obsessive pursuit of science. Glacier research in the field, or even in the office, is a lot of fun for the participants, but it is not great for the family left behind. Now, I have finally acquired some wisdom, and realize how important your kindness, encouragement, and love have been to me in the face of some 41 years of extended absences and continuously pressing deadlines and other crises. I am happy that you could share this precious moment; I love you very much!

“Again, many thanks to you, Garry, to all who supported my nomination, to those who made my career reasonably productive, and to AGU for bestowing this great honor!”

—MARK F. MEIER, University of Colorado at Boulder

Don Kirkham


Mikhail I Budyko


Luna B Leopold


Paul A Witherspoon


Peter S Eagleson


Abel Wolman


Charles Theis


John R Philip


William Ackermann


Harold A Thomas


Walter B Langbein


Honors Contacts

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Rosa Maymi

Director, Engagement and Membership

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Hannah Hoffman

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