H11D-0786
Paleoflood Hydrology and Flood Geomorphology in the Dolores Watershed, CO and UT
Field evidence from six slackwater deposits suggests that 4-7 extreme floods have occurred on the Dolores River since the middle-late Holocene; each of which significantly exceeds the peak historical flood. Preliminary OSL ages for the oldest deposits are corroborated by AMS 14C, dendrochronological, and archeological evidence. In addition to being the first paleoflood study of the Dolores Watershed, this study addresses a critical missing hydroclimatic region in the southwestern U.S.: those areas whose surface hydrology correlates weakly with ENSO variability. Prior paleoflood studies in the Southwest have focused on hydroclimatic regions that correlate strongly with ENSO variability, linking periods of increased flood magnitude and frequency with periods of increased El Niño activity (e.g. Ely, 1997). In this study, we are addressing this critical gap by developing a robust paleoflood chronology based on multiple geochronology techniques. We have made correlations between individual slackwater deposits based on age-control, sediment color, texture, pedogenic development, and stratigraphic position. The correlated slackwater deposits lay within both stable bedrock reaches, as well as mixed bedrock-alluvial reaches. Correlative slackwater deposits between morphologically different reaches are critical because they allow us to make discharge estimates, where the differences may inform us of the degree of channel-bed stability-a critical assumption of paleoflood hydrology. From these differences in discharge estimates, we can infer middle-late Holocene alluvial incision rates.
H11D-0787
Interfacing Single Column Lake and Atmospheric Models: Application over Lake Geneva for Observed and Climate Warming Scenario
A single-column atmospheric model has been coupled to a single-column lake model to simulate present-day as well as future lake temperature profiles following global climate warming conditions. Results of multi-year climate simulations are shown for the case of the deep station SHL2 (309 m) of Lake Geneva, Switzerland. The atmospheric model termed FIZL, is a column version of a limited-area model developed for regional climate modelling based on an off-line downscaling of GCM simulations. It is physically-based and it requires outputs from a previous GCM integration. The issues of local lake climate is addressed by combining precomputed atmospheric large-scale transports of momentum, heat, and moisture, called "the dynamics," and recomputed subgrid-scale parameterized effect (solar and infrared radiation fluxes, and latent and sensible heat fluxes), called "the physics," with the explicit numerical computations of the evolving lower boundary conditions provided by the lake model. The lake model, called k-epsilon (k-e), combines a buoyancy-extended k-e model with a seiche excitation and damping model to predict the diffusivity below the surface mixed layer. In this model, the vertical turbulent diffusivities are determined from the turbulent kinetic energy and energy dissipation. Details of the atmospheric-lake interface module, and a sensitivity analysis of the simulated thermal profiles to this coupler parameters are presented. Finally statistics of the change in the lake thermal profiles is also shown for the case of an equilibrium 2xCO2 global climate warming scenario.
H11D-0788
Modeling future Fraser River temperature with a global climate model
Hydrologic conditions in the Fraser River basin, located in British Columbia, Canada, can have a significant impact on the health and annual survival rates of Pacific salmon. In the final stages of their lifecycle, Pacific salmon migrate upstream in the Fraser River (100 to 1100km) to their spawning beds. Adverse hydrologic conditions, including high flow rates and elevated water temperatures, can prevent the salmon from successfully completing their single lifetime opportunity to reproduce, jeopardizing the future generation s of salmon. We have obtained historical river temperature and discharge for the Fraser River, and we use a global climate model to project changes in both to the end of the 21st century. During the 20th century, increasing trends in water temperature have been observed. We start by discussing the increasing trends in monthly river temperatures, and extend these trends to 2100 through the use of a global climate model. We then work with higher resolution temporal river temperature data to do the same. The monthly analysis is expanded through an examination of observed daily trends, and comparing these to the results of a daily model simulation. The model's daily variability is similar to the observed during the summer for the present climate. The model projections for the last two decades of the 21st century indicate that Fraser River temperature will increase by about 2°C. Of particular importance is the number of days per year when temperatures are above the critical biological threshold for salmon migration of 18°C. For the present climate (20th century), there are 11.2 days per year when river temperatures exceed 18°C. The model projects that this will increase 56.5 days per year by the end of the 21st century (2081-2100). The model also projects temperatures to exceed 19°C an average of 30.3 days per year, and temperatures above 20°C will occur 8.25 days per year during the last two decades of the 21st century. These future conditions may pose a serious threat to the health of the species of Pacific salmon which are susceptible to subtle changes in the basin's hydrologic characteristics. This study is a useful starting point in understanding future water resource requirements and overall ecological fitness in the Fraser Basin. The methodology described herein can be employed in the analysis of other large river basins that may be impacted by future climate change.
H11D-0789
The Impact of Sustained Drought Conditions on a Ground Water Pollutant: Relating the Rise in Trichloroethylene Concentrations in Ground Water to Diminished Flow
Cold Water Spring (CWS) located in the Ridge and Valley Province of the Southern Appalachian Mountains in northeastern Alabama is exhibiting the effects of a local sustained drought. CWS is fed by groundwater from the lower Paleozoic Knox Group, a regional carbonate aquifer. A precipitation-based metric of short- term meteorological drought, the Palmer Drought Severity Index (PDSI), calculated by the National Drought Mitigation Center depicts the magnitude of the drought as increasing in the region since early in the year 2003. Flow of the CWS has been diminishing since the onset of the local drought, and is linearly correlated at 0.6 to the PDSI. The CWS water is contaminated with trichloroethylene (TCE) suspected to be released from a nearby abandoned industrial source. There is a rise in TCE contamination as CWS started to diminish, however, a direct correlation of the TCE concentration to PDSI is not statistically evident. The lack of a statistical correlation between TCE concentration in ground water and the PDSI supports our hypothesis that mobilization of free-phase TCE and its dissolution during periods of drought are multifunctional processes. A lowering of the water table changes the balance of capillary and buoyancy forces which in turn mobilizes the TCE ganglia making it available for dissolution.
H11D-0790
Sensitivity of agricultural runoff to climate change in the San Joaquin Valley watershed of California
The quantification of the hydrological response to climate change and increasing atmospheric CO2 concentrations is required for the proper management of agricultural systems and water resources. This study simulated variations in CO2, temperature and precipitation to quantify the hydrologic response in an intensive agricultural system. The Soil and Water Assessment Tool (SWAT) was used to assess the impact of climate change on agricultural runoff in the San Joaquin watershed in California. The results of this study suggest that atmospheric CO2, precipitation, and temperature changes have significant effects on the yield of sediment, nitrate, total phosphorus, and two pesticides (diazinon and chlorypyrifos) chosen for consideration. As expected, precipitation had a greater impact on agricultural runoff compared to changes in either CO2 concentration or temperature. A change in precipitation of ±10% and ±20% generally altered agricultural runoff proportionally. In comparison to present day reference scenarios, a simulated increase in CO2 concentration while holding temperature and precipitation constant resulted in an increased nitrate, total phosphorus, and chlorpyrifos yield of 4.2, 7.8, and 6.4%, respectively, and a decreased sediment and diazinon yield of 6.3 and 6.4%, respectively. A temperature increase with no precipitation or CO2 concentration change caused a decrease for all agricultural runoff components. Results from this study provide valuable insight into the effects of various climate change scenarios on agricultural runoff and can direct policy makers and agricultural stakeholders in their efforts to create and comply with water quality legislation in a rapidly changing environment.
H11D-0791
The Soil N Source to Stream Runoff During Springmelt is Affected by Soil Freezing: A Snow Manipulation Study in a Forested Watershed in the Snow Belt of Western New York, USA
Although winter has often been referred to as the "dormant season", the term is misleading since many ecological processes can persist at temperatures near or below freezing. The importance of understanding winter ecology is accentuated by concerns about how ecosystems will respond to climate change. Although climatic models of north temperate ecosystems predict greater amounts of winter precipitation in the future, reductions in snowpack are likely to occur due to the increased importance of thaws, sleet, and rain-on-snow events. Without an insulating snowpack, soil ice formation at the onset of winter will persist throughout the winter and/or more frequent freeze-thaw cycles will occur and could affect nutrient cycling and transport during winter and spring. In this study we examined patterns of stream nitrate export during snowmelt in the 696 ha Point Peter Brook Watershed (PPBW), in western, NY. Contrary to what has been observed during late summer/early fall hydrologic events in this watershed, near-surface soil water was an important source of nitrate during springmelt. To test the effects of soil freezing on in situ rates of soil nitrate production (nitrification), presumably a major source of nitrate in the near-surface soil water during springmelt, a snowpack manipulation study was conducted. We established a reference and snow manipulation treatment plots at PPBW. One pair of treatment and reference plots was located in the riparian zone of PPBW while another pair was located on the hillslope. The treatment plots at both landscape positions had significantly greater N mineralization than reference plots. No treatment effect was observed for nitrification in the riparian plots while the hillslope treatment plot had a smaller nitrification rate than the reference hillslope plot. As climate change alters temperate forested ecosystems, especially during winter, the effect of soil freezing should be considered when evaluating differences in N soil cycling and transport.
H11D-0792
Climate Change Effects on Source Waters and Flowpaths in Headwater Catchments of the Colorado Front Range, 1993-2006
Fifteen years of water chemistry data from two alpine watersheds in Green Lakes Valley were used in a multivariate EMMA model to determine potential climate impacts on source waters and flowpaths. The model predicted observed stream concentrations well, with R2 values exceeding 0.8 for most conservative solutes. Hydrograph separations indicate that the proportion of streamflow derived from subsurface pathways increased during dry years at both catchments. During and following the 2002 drought, results suggest that less than 10% of annual streamflow was derived from direct snowmelt at the larger, higher elevation catchment. Hypothesis testing using a multivariate diagnostic model suggests that the source of late-season streamflow at this catchment changed during drought. Based on ionic ratios tending towards rock glacier outflow, water balance calculations from glacier ablation records indicating a missing water source, and a downscaled permafrost model displaying high sensitivity to observed air temperature increases, we suggest that permafrost meltwater may contribute to late-season flow in warm, dry years. This shift in flow paths may also be releasing DIN stored in fossil ice. Preliminary results from long term water quality records at Loch Vale watershed in Rocky Mountain National Park suggest that these observations may be occurring at the regional scale.
H11D-0793
Trends in Stream Water Quality in the Southeastern United States 1973- 2005
As part of the U.S Geological Survey National Water-Quality Assessment Program, water-quality data for 333 streams in 8 states of the Southeastern United States were assessed for trends from 1973 to 2005. Forty- three USGS sampling sites were examined for trends over periods within the 1973-2005 timeframe in pH, specific conductance, in concentrations of major dissolved constituents, and nutrients. An additional 290 sites from the U.S. Environmental Protection Agency STORET database were tested for trends in nutrient concentrations. The seasonal Kendall test or Tobit regression was used to detect monotonic trends. Previous assessments of trends for the Southeast showed: (1) Increases (1960-80) in sulfate and decreases in alkalinity, possibly because of atmospheric inputs, (2) Increases in dissolved constituents in North Carolina streams (1960-80), that correlated with increased manufacturing employment and population and decreasing cropland acreage, (3) Increased (1970-1980) nutrient concentrations in many southeastern basins, (4) Clusters of increases and decreases of nitrogen concentrations during 1980-2000, (5) Stable total nitrogen concentrations, with ammonia and organic nitrogen decreasing and nitrate concentrations increasing, possibly as a result of changes in wastewater- treatment processes, (6) Distinct reductions in total phosphorus concentrations that are related to phosphate detergent bans and changes in wastewater-treatment processes implemented from 1972 to 1999, (7) Decreases in total nitrogen (1995-2003) observed in streams in Alabama, Georgia, and North Carolina, and (8) Sulfate, nitrate, and calcium reductions in precipitation during 1981-1998. The 1973-2005 assessment showed that dissolved constituents have increased in many streams in the Southeast during the last 30 years. Specific conductance, an indicator of dissolved ions in water, increased at 62 percent of the sites, and pH increased at 31 percent of the sites. Long-term decreasing trends in total nitrogen were detected at 49 percent of the sites. Ammonia decreased from 1973 to 2005 at 27 percent of the sites and nitrite plus nitrate concentrations decreased at 32 percent of the sites. The results indicate that the principal change in stream nitrogen concentrations is a result of changes change in ammonia and organic nitrogen in streams, which likely are a result of improved municipal wastewater-treatment methods. Concentrations of phosphorus have decreased over the last 35 years which coincides with phosphate- detergent bans and changes in wastewater treatment that were implemented beginning in 1972. Decreasing trends in total phosphorus were detected at 56 percent of the sites tested. Multiple regression analysis was used to examine associations of annual median constituent concentrations and regional landscape and agricultural variables. The analysis indicated a relation between changes in atmospheric inputs and agricultural practices and changes in water quality. A long-term water-quality and landscape trends-assessment network for the Southeast is needed to assess changes in water quality over time in response to variations in population, agricultural, wastewater, and landscape variables. Understanding changes in stream chemistry over time in relation to with changes in population, agriculture, and wastewater treatment technology in the Southeast will assist water-resource managers in developing protection strategies.
H11D-0794
The Role of Climatic Variability on Rio Grande Salinity and Water Balances
The upper Rio Grande/ Rio Bravo extends ~1,200 km between its headwaters in southern Colorado (USA) and the USA/Mexico border region. Like many arid region rivers, it exhibits reductions in streamflow and degrading water quality with distance downstream as a result of decreasing inflows, increasing evapotranspiration, and the addition of natural and anthropogenic solutes. From 2000 to 2007 we conducted detailed biannual synoptic sampling of the Rio Grande from its headwaters in Colorado to ~150 km south of El Paso, Texas to evaluate how these processes result in the observed basin-scale water and solute balances. This period coincides with a severe regional drought, as well as the 8th wettest summer monsoon in the region, allowing us to assess how basin processes which control water quality respond to periods of climatic variability. We employed multiple environmental tracers to help identify dominant hydrological processes and the causes of salinization. Our O and H isotopic results indicate that runoff from high-elevation areas in Colorado and northern New Mexico - primarily as snowmelt - is the dominant source of river water, although runoff from summer precipitation can be locally and seasonally significant. This water then exhibits progressive evaporation with distance downstream, with the greatest evaporation occurring at Elephant Butte Reservoir. At the same time, the total dissolved solids content (TDS) increases from less than 50 mg/L in headwaters of Colorado to over 2000 mg/L south of El Paso, Texas. Water balance estimates and our O and H isotope results indicate that evapotranspiration alone is not sufficient to explain the salinization. The results of our synoptic surveys found that salinity did not increase as a simple function of distance downriver but rather occurred in a series of steps, identified as discharge of deep, saline, ground water. During the course of the drought we observed a progressive increase in salt concentrations and more localized increases in O and H isotopes in areas with significant evaporation (e.g., from Elephant Butte Reservoir and wetted sandbars in the Albuquerque region).
H11D-0795
Climate driven changes in salinity of East African Rift Valley lakes through 2050
Lakes in endorheic basins are useful sentinels of climate change. Increases in net evaporation due to higher temperature and lower precipitation can lead to lower lake level and higher salinity with concurrent decreases in biodiversity and potentially an increase in dust emissions from more-frequently dry lake beds. We use downscaled output from three different coupled atmosphere-ocean general circulation models as input to a hydrologic model in a GIS-framework to estimate changes in lake level and salinity of the endorheic lakes in the East African Rift Valley. Overall, there is a drying trend through 2050 with salinity increasing to various degrees in the target lakes; however, some emission scenarios under certain model runs predict a large enough precipitation increase to affect a decrease in annual net evaporation and hence an increase in water level and decrease in salinity. We explore the fundamental uncertainties in the GCM predictions and attempt to provide robust bounds on the estimates to make policy-relevant predictions.
H11D-0796
Regional aspect of highly water-stressed population estimated by world water resources under SRES scenarios
Global and regional populations lived in highly water-stressed basin for a function of the temperature were estimated using the socio-economical data and the outputs of GCMs. In global, the highly water-stressed population in scenario A2 rapidly increased when the anomaly of temperature is exceeding to about +1.5 deg.. In the case of the scenario A1b, the gradient of increase of highly water-stressed population was less than that in the case of the scenario A2. When the value of temperature anomaly was exceeding to about + 1.5 deg., the gradient of increase of highly water-stressed population became loose. On the other hand, the highly water-stressed population in the scenario B1 decreased when the temperature anomaly was exceeding to about +1.2 deg.. According to the estimation of the highly water-stressed population when the effect of climate change was ignored (that is, runoff was not changed), the highly water-stressed population was almost same. This result implied that it is strongly contributed by not the climate change but the socio- economical factors (ex; an irrigated area, increase of industrial water use, increase of population itself). Parry et al. (2001) pointed out that the influence on the water risk by the climate change is serious when the anomaly of temperature is exceeding to +2 deg.. However, our assessment disagrees with their assignment. When the highly water-stressed population assessment is estimated within the social elements (ex., the increase of irrigation demand, industrial demand, and population itself), the climate change is not so effective. Part of this study was financially supported by the Global Environment Research Fund, "S-4" and "S-5", from the Japanese Ministry of the Environment.
H11D-0797
Influences of Climatic Variability on the Water Resources of Lebanon, Mediterranean Basin
Climatic variability and change, as a worldwide geo-environmental issue, has become more pronounced in many regions of the world, especially in arid and semiarid regions. Increased global temperatures have led to fluctuations in the climate and hydrology as evidenced by changes in the frequency or intensity of precipitation and then extent and depth of snow cover. This, in turn, has resulted in decreased water supply in rivers and springs. Along the Eastern side of the Mediterranean, Lebanon as well is affected by climatic variability. This is reflected mainly in its water resources, which show a sharp decrease in their volume, affecting the country's water supply. Therefore, water shortages have become a national issue in Lebanon. Studying this phenomenon can be achieved through analyzing different indices of surface and subsurface water resource availability. Comparative analysis of different hydroclimatic records, both qualitative and quantitative, was performed. In addition, remotely sensed data were utilized, notably to fill gaps in the existing records. Results show obvious descending trends in the amount of available water. The precipitation rates revealed a decrease of 12-16% over 30 years. As for flow in rivers and springs, the decrease in the discharge range was between 23% and 29%, and groundwater levels were depleted by several meters. Additionally, snow cover area decreased from 2500 km2 to 1900 km2 over the last two decades. Over-exploitation of water resources has exacerbated this problem. The results are quite alarming and expose a dramatic situation in the water resources of Lebanon. Therefore immediate interventions such as better resource management practices and effective water conservation measures need to be undertaken.
H11D-0798
Climate Change Impact on Groundwater Recharge: A Case Study in Taiwan
Climate change may result in variety of climate and streamflow characteristics. These will further induce influences of groundwater recharge. Therefore, this study assessed the impact of climate change on groundwater recharge through evaluating the change of streamflow under different scenarios. Projection of precipitation or temperature impacted by climate change is of great uncertainty, thus three Global Circulation Models (GCMs), i.e. HADCM3, CGCM2 and GFDL, with two kinds of climate change scenarios, i.e. A2 and B2, are adopted in this study to reduce the uncertainty. Simple downscaling method is utilized to downscale the precipitation and temperature data from global scale to local scale, which is then used as input in the Hydrologiska Byråns Vattenbalansavdelning (HBV) model to project the change of streamflow in the period of 2010 to 2039. Besides, a groundwater numerical model of Taipei basin in Taiwan will be constructed by Processing Modflow and verified by collected historical data. River elevation is simulated by HEC-RAS model with observed streamflow data and streamflow projected by HBV model, and the river package in the PM model is used to simulate the groundwater recharge for now and future scenarios. Finally, monthly and seasonal groundwater recharge impacted by climate change will be investigated for different GCMs and scenarios.
H11D-0799
Temporal and Spatial variations of small river dissolved loads in Taiwan
Mountainous river is a major source of suspended particles exported to the ocean. A number of studies focused on fate of these particles entering the ocean. However, little information is available concerning dissolved phases in small rivers. Is the chemical weathering controlling small river water dissolved load and particle? Is the physical denudation play a more important role? The objectives of this study are to understand spatial and temporal variations of dissolved major ions in the small rivers of Taiwan and to unravel factors controlling dissolve phases and small river particle load. River major ions (Ca, Mg, Na, K, chloride, silicate, sulfate and bicarbonate) compositions were sampled monthly at 18 stations in 12 rivers in 2007. Large spatial and temporal variations in major ion concentrations were found in study rivers. Major ions concentration in rivers of the southwestern region (Erjen, Tsengwen, Kaoping ) are higher than those of northeastern region (Hoping, Hualien, Xiuguluan). Erjen and Tzengwen River are the highest in major ions concentrations among all rivers of Taiwan. Total dissolved solid displayed similar regional variations as the major ions. TDS in rivers of the southern region are higher than those of the northern region. In addition, major ions in rivers of the southern region showed strong temporal variations. During summer, most major ions and TDS are lower than those during winter. Two major factors are important in controlling the observed temporal and spatial variations, change in seasonal precipitation and rock composition. Most rain water precipitated during summer season. Siliceous sandstone is the predominant type in the northern region while poor to un-cemented mudstone is the main type of rock in the southwestern region.
H11D-0800
Effects of climate variability and extremes on surface water quality across different spatiotemporal scales
Potential changes in runoff and water quality in response to climate change might pose a great challenge for
the management of freshwater resources in East Asia, given large seasonality in monsoon rainfalls and huge
water demands from the fast growing economy. To obtain baseline data for the assessment of ¡®climate
risks' to surface water quality from climate variability and extremes, a regional collaborative research has
been conducted over the last three years, involving water quality monitoring at various time scales at 12
watersheds of 8 East Asian countries. Cross-site comparison of seasonal differences in major water quality
parameters showed higher concentrations of total suspended solid (TSS) and dissolved organic carbon
(DOC) in the monsoon than in the dry period at most of the monitoring sites. TSS concentrations were
exceptionally high at Thai and Lao watersheds along the upper reach of the Lower Mekong River Basin, while
seasonal differences in TSS concentrations were relatively small at the watersheds with larger forest
coverage or less steep topography. The concentrations of dissolved metals were usually lower in the
monsoon period despite the higher concentrations of DOC that often exerts a strong control on dissolved
metals in surface waters. Lower concentrations of dissolved metals during the monsoon concurred with
higher concentrations of acid-recoverable metals measured as a surrogate of total metals, suggesting
increases in particulate metals in response to rainfall-induced increases in suspended sediments. Intensive
storm sampling conducted at the watersheds with contrasting patterns of land use and topography in Korea
and Lao PDR showed flash responses of the terrestrial export of sediments and associated metals during
successive heavy monsoon rainfall events, particularly from the steep, deforested hillslopes. Taken together,
the results suggest the importance of sediments in regulating metal concentrations in surface waters and
highlight climate sensitivity of surface water quality at deforested watersheds on steep mountainous terrain.
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