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[1] Considering that past climate changes have significantly impacted groundwater resources, quantitative predictions of climate change effects on groundwater recharge may be valuable for effective management of future water resources. This study used 16 global climate models (GCMs) and three global warming scenarios to investigate changes in groundwater recharge rates for a 2050 climate relative to a 1990 climate in the U.S. High Plains region. Groundwater recharge was modeled using the Soil-Vegetation-AtmosphereTransfer model WAVES for a variety of soil and vegetation types representative of the High Plains. The median projection under a 2050 climate includes increased recharge in the Northern High Plains (þ8%), a slight decrease in the Central High Plains (À3%), and a larger decrease in the Southern High Plains (À10%), amplifying the current spatial trend in recharge from north to south. There is considerable uncertainty in both the magnitude and direction of these changes in recharge projections. Predicted changes in recharge between dry and wet future climate scenarios encompass both an increase and decrease in recharge rates, with the magnitude of this range greater than 50% of current recharge. On a proportional basis, sensitivity of recharge to changes in rainfall indicates that areas with high current recharge rates are least sensitive to change in rainfall and vice versa. Sensitivity analyses indicate an amplification of change in recharge compared to change in rainfall, and this amplification is in the range of 1-6 with an average of 2.5-3.5 depending upon the global warming scenario.

1-2 ka for the desert's southeastern margin is inferred from radiocarbon. These results reveal that some replenishment to the desert aquifer is occurring but at a rate much lower than previously suggested, which is relevant for water resources planning in this ecologically-sensitive area.

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[2000][2001][2002][2003][2004][2005][2006][2007][2008][2009] period was estimated at a 1-km spatial resolution as the difference of mean annual precipitation (P) and evapotranspiration (ET). Monthly P values came from the PRISM dataset, while monthly ET values were derived from linear transformations of the MODIS daytime land-surface temperature values into pixel ET rates with the help of ancillary atmospheric data (air temperature, humidity, and global radiation). The study area receives about 73 mm of recharge (with an error bound of ±73 mm) annually, which is about 14 ± 14% of the regional mean annual P value of 533 mm. The largest recharge rates (about 200 ± 85 mm or 30 ± 12% of P) occur in the south-eastern part of the Sand Hills due to smoother terrain and more abundant precipitation (around 700 mm), while recharge is the smallest (about 40 ± 59 mm or 10 ± 14% of P) in the western part, where annual precipitation is only about 420 mm. Typically, lakes, wetlands, wet inter-dunal valleys, rivers, irrigated crops (except in the south-eastern region) and certain parts of afforested areas in the south-central portion of the study area act as discharge areas for groundwater.