Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78713-8924, USA.
Proc Natl Acad Sci U S A. 2012 Jun 12;109(24):9320-5. doi: 10.1073/pnas.1200311109. Epub 2012 May 29.
Aquifer overexploitation could significantly impact crop production in the United States because 60% of irrigation relies on groundwater. Groundwater depletion in the irrigated High Plains and California Central Valley accounts for ~50% of groundwater depletion in the United States since 1900. A newly developed High Plains recharge map shows that high recharge in the northern High Plains results in sustainable pumpage, whereas lower recharge in the central and southern High Plains has resulted in focused depletion of 330 km(3) of fossil groundwater, mostly recharged during the past 13,000 y. Depletion is highly localized with about a third of depletion occurring in 4% of the High Plains land area. Extrapolation of the current depletion rate suggests that 35% of the southern High Plains will be unable to support irrigation within the next 30 y. Reducing irrigation withdrawals could extend the lifespan of the aquifer but would not result in sustainable management of this fossil groundwater. The Central Valley is a more dynamic, engineered system, with north/south diversions of surface water since the 1950s contributing to ~7× higher recharge. However, these diversions are regulated because of impacts on endangered species. A newly developed Central Valley Hydrologic Model shows that groundwater depletion since the 1960s, totaling 80 km(3), occurs mostly in the south (Tulare Basin) and primarily during droughts. Increasing water storage through artificial recharge of excess surface water in aquifers by up to 3 km(3) shows promise for coping with droughts and improving sustainability of groundwater resources in the Central Valley.
含水层超采会对美国的作物生产产生重大影响，因为 60%的灌溉依赖地下水。自 1900 年以来，灌溉用的美国高平原和加利福尼亚中央谷地的地下水耗竭量占美国地下水耗竭总量的50%。一张新开发的高平原补给图显示，高平原北部的高补给量导致了可持续的抽水量，而高平原中部和南部的低补给量则导致了 330 立方公里的化石地下水的集中耗竭，这些地下水主要是在过去的 13000 年中补给的。地下水的耗竭高度集中，大约三分之一的耗竭发生在高平原土地面积的 4%。根据目前的耗竭率推断，在未来 30 年内，高平原南部的 35%将无法支持灌溉。减少灌溉用水的抽取量可以延长含水层的寿命，但不会实现对这种化石地下水的可持续管理。加利福尼亚中央谷地是一个更具活力、经过工程设计的系统，自 20 世纪 50 年代以来，地表水的南北调水导致了7 倍的更高补给量。然而，由于对濒危物种的影响，这些调水受到了监管。一个新开发的中央谷地水文模型显示，自 20 世纪 60 年代以来，地下水的耗竭总量为 80 立方公里，主要发生在南部（图莱里盆地），并且主要发生在干旱时期。通过将多余的地表水人工补给到含水层中，增加 3 立方公里的储水量，有望应对干旱，并提高加利福尼亚中央谷地地下水资源的可持续性。
