The rapid depletion of groundwater resources in key U.S. agricultural regions could portend future vulnerabilities in growing the nation’s food, according to a new study. In an assessment of water supplies in California’s Central Valley and the High Plains of the central U.S. — which runs from northwest Texas to southern Wyoming and South Dakota — University of Texas researchers found that in many places water is being used faster than it can be replenished, and that some regions may be unfit for agriculture within decades. According to their findings, farmers in California’s Central Valley, a region known as the nation’s “fruit and vegetable basket,” used enough water during a 2006-2009 drought to fill Lake Mead, the nation’s largest man-made reservoir. In the High Plains, a major grain-growing region, about one-third of groundwater depletion occurs in just 4 percent of the land area. At current rates of water depletion, some parts of the High Plains, including the Texas Panhandle and western Kansas, will be unable to support irrigated agriculture within a few decades, according to the study, published in the journal Proceedings of the National Academy of Sciences.