Some regions of the United States rely partially—and others, such as Florida, mainly— on groundwater for drinking, residential use, and agriculture. According to the U.S. Geological Survey (USGS, 2004), total groundwater withdrawals in the country in 2000 amounted to 84,500 million gallons per day—about one quarter of total freshwater withdrawals. In the central United States, usage of the Ogalalla aquifer, mainly for agriculture, is withdrawing groundwater much faster than it can be recharged (Alley et al., 1999) and other aquifer systems are also being depleted (USGS, 2003). Significant changes in future rainfall rates will create additional vulnerabilities associated with groundwater usage.

The impacts of climate change on groundwater are far from clear; in fact, little research effort has been devoted to this topic. Changes in precipitation and evaporation patterns, plant growth processes, and incursions of seawater into coastal aquifers will all affect the rate of groundwater recharge, the absolute volume of groundwater available, groundwater quality, and the physical connection between surface and groundwater bodies (USGCRP, 2009a). Already, as climate change-driven impacts and other pressures on water resources unfold, water managers in drier regions of the United States find themselves confronted with the need to expand groundwater withdrawal and develop groundwater recharge schemes and infrastructure. The inconsistent regulation of groundwater and surface water from state to state and the lack of readily available legal mechanisms to link ground- and surface-water management—even where they are physically linked—makes comprehensive, integrated water management difficult.

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