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<br />A common response to droughts is to drill more wells. <br />Increased use of ground water may continue after a drought <br />because installation of wells and the infrastructure for delivery <br />of ground water can be a considerable investment. Thus, a <br />drought may lead to a permanent, unanticipated change in <br />the levei of ground-water development. Use of ground-water <br />resources for mitigating the effects of droughts is likely to be <br />most effective with advance planning for that purpose. <br />Ground-water systems tend to respond much more <br />slowly to short-term variability in climate conditions than do <br />surface-water systems. As a result, assessments of ground- <br />water resources and related model simulations commonly <br />are based on average conditions, such as average annual <br />recharge or average annual discharge to streams. This use <br />of average conditions may underestimate the importance <br />of droughts. <br />The effect of potential long-term changes in climate, <br />including changes in average conditions and in climate <br />variability, also merits consideration. Climate change could <br /> <br />affect ground-water sustainability in several ways, including <br />(1) changes in ground-water recharge resulting from changes <br />in average precipitation and temperature or in the seasonal <br />distribution of precipitation, (2) more severe and longer lasting <br />droughts, (3) changes in evapotranspiration resulting from <br />changes in vegetation, and (4) possible increased demands <br />for ground water as a backup source of water supply. Surficial <br />aquifers, which supply much of the flow to streams. lakes, <br />wetlands, and springs, are likely to be the part of the ground- <br />water system most sensitive to climate change; yet, limited <br />attention has been directed at determining the possible effects <br />of climate change on shallow aquifers and their interaction <br />with surface water. <br />In summary, consideration of climate can be a key, but <br />underemphasized, factor in ensuring the sustainability and <br />proper management of ground-water resources. As increasing <br />atlention is placed on the interactions of ground water with <br />land and surface-water resources, concerns about the effects <br />of droughts, other aspects of climate variability, and the poten- <br />tial effects of climate change are likely to increase. <br /> <br /> <br />During the final preparation of this report In the summer of 1999, much of the Eastern United States was experiencing <br />a severe drought, causing shallow wells to go dry In many areas. A few inches of rainfall in late August returned lawns to <br />a healthy green color in this part of rural Virginia (note wellhead near home). However, these storms had little effect on <br />ground-water levels because of the large cumulative moisture deficit In the unsaturated zone. Up to 6 inches or more of <br />sustained precipitation from Tropical Storm Dennis over Labor Day weekend had a more substantial effect on ground- <br />water levels, but parts of the Eastern United States unaffected by the tropical storm remained dry. In mid-September, <br />Hurricane Floyd brought additional rain to the region. The drought Intensified concerns about development of ground- <br />water resources and the effects of possible Interference between pumping wells, particularly in rapidly developing parts <br />of the Piedmont where some of the fastest growing counties In the Nation are located. <br /> <br />21 <br />