H12D-01
Regional assessments of groundwater resources by uses of satellite GRACE and GRAPHIC network in Western Australia
Groundwater is an important part of the hydrologic cycle and a valuable natural resource. Global and regional groundwater resources is threatened by human activities and the uncertain consequences of climate change, however, little is known about how groundwater might respond to climate variability and affect the current availability and future sustainability of groundwater resources. UNESCO-GRAPHIC (Groundwater Resources Assessment under the Pressures of Humanity and Climate changes) project which was established at 2004, promotes and advances sustainable groundwater management considering projected climate change and linked human effects. GRAPHIC provides a platform for exchange of information through case studies, thematic working groups, scientific research, and communication. One of the tools for evaluating the change in global/regional groundwater resources is the use of satellite GRACE (Gravity Recovery And Climate Experiment) which was launched at 2002. In this study, the satellite GRACE and GRAPHIC network have been used for evaluating regional groundwater resources assessment. Inter-annual changes in land water storage evaluated by GRACE show the decreasing trend during the last 6 years at southwest of Australia and southeast of Australia including Marry-Darling basin, due to mainly decrease in precipitation. On the other hand, the land water storage in northern Australia increased during the last 6 years due to increase in precipitation. The long term trend of groundwater level in Western Australia also showed the decreasing trend during the last 6 years. The differences between GRACE and in situ groundwater level have been compared depending on hydrogeology and land cover/use, under the similar meteorological condition in Western Australia.
H12D-02
Golan Heights Groundwater Systems: Separation By REE+Y And Stable Isotopes
In a semi-arid to arid country like Israel, all freshwater resources are under (over-) utilization. Particularly, the Golan Heights rank as one of the most important extraction areas of groundwater of good quality and quantity. Additionally the mountain range feed to a high degree the most important freshwater reservoir of Israel, the Sea of Galilee. Hence, knowing the sources and characters of the Golan Heights groundwater systems is an instantaneous demand regarding sustainable management and protection. Within the "German-Israeli-Jordanian-Palestinian Joint Research Program for the Sustainable Utilisation of Aquifer Systems", hundreds of water samples were taken from all over the Jordan-Dead Sea rift-system to understand groundwater flow-systems and salinisation. For that purpose, each sample was analysed for major and minor ions, rare earth elements including yttrium (REY) and stable isotopes of water (d18O, d2H). The REY distribution in groundwater is established during infiltration by the first water-rock interaction and consequently reflects the leachable components of sediments and rocks of the recharge area. In well- developed flow-systems, REY are adsorbed onto pore surfaces are in equilibrium with the percolating groundwater, even if the lithology changes (e.g. inter-aquifer flow). Thus, groundwater sampled from wells and springs still show the REY distribution pattern established in the recharge area. Since high temperatures do not occur in Golan Heights, d2H and d18O are less controlled by water-rock interaction than by climatic and geomorphological factors at the time of replenishment. Applying the REY signature as a grouping criterion of groundwaters, d18O vs. d2H plots yield a new dimension in interpreting isotope data. The combined use of hydrochemical and isotopic methods enabled us to contain the areas of replenishment and the flow-paths of all investigated groundwater in the Golan Heights. Despite location, salinity or temperature of spring or well waters, stable isotopes showed, that the main area of recharge is the elevated Hermon-Massif, with high annually precipitation amounts. The major element composition of fresh water well Alonei HaBashan 3, situated in the basaltic Upper Golan Heights, is defined by a pre-Neogenic limy aquifer and the contact to basalts. However, REY pattern refer to a calcareous infiltration area. Stable isotope signatures are lighter than in the recharge of comparable elevated Upper Galilee. Further to the south, in the Yarmouk gorge hot Mezar springs occur, which show stable isotope signatures even lighter than in water of Alonei Habshan 3. Both, REY pattern and hydrochemistry show infiltration into and contact to the Sr-rich limestone aquifer of the Mt. Scopus group. That adds up to an infiltration area some 50 km to the north, the nearest elevated area where carbonates crop out. Nearby Mezar, hot Hammat Gader springs occur, which show comparable isotopic signatures and hydrochemical composition. However, the REY-patterns indicate infiltration in basalts. By means of those three examples we could show, that the use of a combined hydrochemical and isotopic approach reveals complex and large-scale groundwater infiltration- and flow-systems much better than a focused view on a specific band of elements.
H12D-03
Salinity is Reduced Below the Evaporation Front During Soil Salinization
Nearly 50% of irrigated lands in arid and semi-arid regimes have salinization problems. Salinization is generally caused by salts carried to the soil surface by capillary rising water and occurs under very dry conditions, when vapor fluxes become the main water flux mechanism. Despite its global importance, actual salinization mechanisms are only poorly understood. Soil salinization is generally studied by means of water and salt balances without entering on small scale processes. This may suffice for explaining large scale behavior but hardly for designing remediation practices. The objective of this work is to study the solute transport under evaporation conditions. We have performed laboratory experiments and modelled them. We have built open sand columns initially saturated with an epsomite (MgSO4•7H2O) solution. Evaporation was driven by an infrared lamp and proceeded until the overall saturation fell down to 0.32. Results imply that water vapor flows not only upwards above the evaporation front, but also downwards beneath this front, where it condensates. Condensation causes the dilution of the solution. That is, concentrations fall below the initial values. The experiments have been modelled with the program RetrasoCodeBright, which couples non isothermal multiphase flow and reactive transport. Reproducing the observations required modifying the standard retention and relative permeability functions to include oven dry conditions. The model reproduces the observed concentration, water content and temperature profiles along the column and confirms the existence of condensation and decrease of salt concentration below the evaporation front. The model also allows us to distinguish the relevance between the advective and diffusive vapor fluxes, showing that the latter is, by far, the largest. The mechanism displays positives feedbacks, as condensation will be most intense in areas of highest salinity, thus diluting saline water that may have infiltrated.
H12D-04
21st-Century Sea Level Rise, Economic Growth, and Seawater Intrusion in Coastal Aquifers of California
21st-century sea-level rise predictions for California's coastal waters range from 0.10 m to 0.80 m. In coastal semiarid aquifers of California with low topographic relief and heavy groundwater pumping this might lead to pervasive landward migration of seawater plumes. In other coastal aquifers with pronounced seaward hydraulic gradient, the effect of sea-level rise might not be as pronounced. This paper implements a variable- fluid-density, 3-D, finite element numerical flow and transport model to assess the evolution of coastal aquifer salinity during the 21st century due to sea level rise by ice melting and oceanic thermal expansion, and by extraction driven by economic and population growth in semiarid coastal regions of California. The paper focuses on contrasting two different hydrogeologic settings in two heavily mined coastal aquifer with a state- of-the-art numerical simulation model.
H12D-05
Use of reactive transport models to quantify changes in baseflow composition due to changes in the seasonal rainfall distribution
Future climate scenarios predict a shift in the seasonal distribution of precipitation throughout large areas of the world. Changes in the timing of recharge events are expected to have an impact on groundwater quality and hence, on the baseflow of streams and rivers. Factors that control the seasonal variability of the chemical composition of the recharge water include seasonal differences in (i) temperature and partial CO2 pressure in the soil zone, (ii) evapotranspiration rates and (iii) vegetation characteristics. In addition, residence times in the aquifer may be affected when the recharge regime changes, which may impact kinetically-controlled chemical mass transfers. In this study, a reactive transport model (PHT3D 2.0) was used to quantify the potential effect of a shift in the distribution of groundwater recharge over the year on the chemical composition of baseflow of a stream draining a hillslope. The only factor that was considered to control the recharge composition was the seasonal regime in the CO2 pressure in the soil zone. The recharge conditions that were evaluated ranged from an even distribution throughout the year to all recharge occurring during the wet season. Partial pressures of CO2 in the soil zone were varied from 0.001 atm in the wet season (winter) to 0.21 atm in the dry season (summer) and recharge water was assumed to be in equilibrium with the soil atmosphere. Model outcomes were generalized by considering different lithologies and chemical conditions, i.e., limestone dissolution under open and closed conditions with respect to CO2 and kinetically controlled silicate dissolution. In all cases, a decrease of total inorganic carbon and an increase of pH in the stream occur if the proportion of winter recharge increases. Simultaneously, the concentrations of the base cations like Ca and Na decrease up to 50%. These results suggest that the predicted changes in the timing of recharge events due to climate variability may have a profound impact on weathering rates and the chemical composition of surface waters. Future studies will focus on extending the model to include more of the potential factors affecting the groundwater recharge composition and to upscale results to assess global impacts.
H12D-06
Linkage Of A Finite Element Flow Model With A Soil Moisture Model: Challanges Under Semiarid Conditions
The arid to semiarid Middle East is a region of extreme growth of population. Hence, the rare and over- expoitated water resources in that region have to be more protected against antropogenic and geogenic pollution. One way to help solving that complex issue is to develop an intelligent and integrated strategy to manage all available water resources, which is the aim of the multilateral SMART-project in the Lower Jordan Valley. To generate such an IWRM, all water resources (groundwater, surface runoff, waste water) of the valley and its shoulders have to be quanti- and qualitatively evaluated. The strategy of SMART is to upscale knowledge, extracted from local catchment areas to the project scale, which covers the area between Sea of Galilee, Jerusalem, Dead Sea and Amman. The study areas of the here presented sub-project are the Wadis Qilt (Palestine) and Al Arab (Jordan). The aim of the sub-project is to evaluate natural resources on catchment scale by combining hydrochemical and hydraulical methods to develop a high precision model. Concerning the quantification of the system, two seperated models will be linked: a numerical finite element flow-model for the groundwater passage and a new devolped hydrological model JAMS, which is excellently prepared for humid conditions. The power of JAMS is the highly accurate assessment of soil moisture balance and consequently of surface runoff and groundwater recharge. However, the empirical equations and input parameters have to be adjusted onto the conditions of the semiarid Wadi Al Arab and the arid Wadi Qilt. After the adaption of JAMS, the spatially and temporarily differentiated calculation of runoff and groundwater recharge is possible. Beside climatic gradients, the key issue is, to correctly evaluate the evapotranspiration in respect to the different classes of landuse. In the study area Wadi Al Arab, the groundwater recharge was calculated as area-indicated output parameter of JAMS. This output was used to be the spatial differentiated input parameter of the numerical flow model. The advantage is the direct comparability of the finite-element meshs of JAMS and FeFlow. However, the individual definitions of values (recharge, base flow, exfiltration of JAMS, infiltration of FeFlow, etc.) of both models have to be linked by an interface between both systems. One of the biggest challenges is the temporal discretization of recharge between leaving soilcrust and entering groundwater table. In fact, the target was to evaluate the effects of retardation of the unsaturated zone in dependence to the hydraulic parameters of the entire groundwater reservoir.
H12D-07
Ground-Water Availability Responses to Climate Variability on Interannual to Multidecadal Timescales, Mississippi Embayment Regional Aquifer System, USA
Climate variability on interannual to multidecadal timescales has important implications for the availability of global ground-water resources. Spatiotemporal patterns in precipitation, air temperature, evapotranspiration, drought, streamflow, and recharge are partially controlled by the variability in climate forcings on interannual to multidecadal timescales. Because these climate-varying conditions can augment or diminish human stresses (pumping) on ground water, the responses in water levels and ground-water storage can be dramatic when different climate cycles lie coincident in a positive (wet/cool) or negative (dry/warm) phase of variability. Thus, understanding climate cycles on these timescales has particular relevance for management decisions during drought and for ground-water resources close to the limits of sustainability. The objective of this study is to quantify the response of ground-water resources in the Mississippi Embayment Regional aquifer system (USA) (>181,000 km2) to natural climate variability on interannual to multidecadal timescales and to use that knowledge to improve calibration of ground-water availability modeling that will predict the responses in this regional aquifer system over the next twenty-five to fifty years. The Mississippi Embayment Regional aquifer system is an important water resource used predominantly for public-drinking and agricultural supply across parts of seven States (Alabama, Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee). Using singular spectrum analysis of long-term hydrologic time series, the signal of ground-water pumping was removed and natural variations were identified in all tree ring, precipitation, air temperature, and ground-water level time series as partially coincident with known climate forcings; including the El Nino/Southern Oscillation (2 to 6 year cycle), the Pacific Decadal Oscillation (10 to 25 year cycle), and the Atlantic Multidecadal Oscillation (50 to 80 year cycle). Climate-varying recharge and water-level fluctuations in the aquifer are most significantly correlated to an interdecadal (16 to 21 year) cycle that is most consistent with the Pacific Decadal Oscillation. The results of this study support the conclusion that understanding natural climate variability is a necessary step toward predicting and managing the future availability of ground-water resources. Modeled responses of the aquifer to these natural climate forcings over the next fifty years will be presented.
H12D-08
Modeling Future Climate Change Impacts on Groundwater in Mountainous Valley-Bottom Aquifers
Groundwater resources within many mountainous valley-bottom aquifers are increasingly threatened by increased demand for water due to population growth and intensification of agriculture. The semi-arid to arid conditions in such valley bottom areas make them particularly sensitive to climate change owing to the strong dependence of evapotranspiration rates on temperature, and potential shifts in the precipitation amounts and timing. Over the past several years, a series of case studies have been conducted in southern British Columbia, Canada to model potential impacts of future climate change on groundwater recharge and groundwater levels. The study areas represent a range of current hydro-climatic regimes, spanning wet to semi-arid to arid, and focus on alluvial aquifers, situated in mountainous valleys. The same overall methodology and codes were used to assess climate change impacts in each aquifer system. Downscaled climate data from one or more global climate models (GCMs) were used to drive the recharge model. Downscaling was particularly challenging for precipitation due to the inherent difficulty for GCMs to simulate representative precipitation for mountainous regions. Temperature data were generally successfully downscaled. Solar radiation changes were estimated directly from the GCM data. To compensate for difficulties in downscaling, shifts in climate, from present to future-predicted, were applied to the LARS-WG stochastic weather generator to generate daily stochastic weather series for current and future time periods. Direct recharge via precipitation was modeled for each time period using the generated weather series. Spatial recharge was mapped from one-dimensional recharge simulations conducted using the HELP hydrologic model. Indirect recharge from rivers or streams was variably adjusted to account for shifts in timing and/or discharge amount based on future runoff predictions. Groundwater levels for current and future time periods were simulated using MODFLOW. Overall, shifts in direct recharge are generally small, but are highly influenced by selection of downscaling method or GCM, suggesting that prediction of future recharge is highly dependent on the model selected. Thus, when undertaking recharge modelling studies for future climate change, it is important to consider a broader range of models. Shifts in the timing of river discharge proved to have the strongest impact on groundwater levels in one aquifer that is highly connected to this river throughout the valley bottom, thus, consideration of changes in the timing of runoff due to earlier snowmelt, for example, should be explicitly included in models.