The researchers found the Arabian Aquifer System, which supplies water to more than 60 million people, to be the most overstressed in the world, followed by the Indus Basin aquifer of northwestern India and Pakistan, and the Murzuk-Djado Basin in northern Africa. The aquifer beneath California's Central Valley, for instance, was labeled as highly stressed. Some of the regions with the most pronounced depletion of groundwater also are major farming areas. Thirteen of those declining aquifers - about one-third of the total - were classified as being "highly stressed," "extremely stressed," or "overstressed," with the most severe situations seen in dry areas where little or no water is seeping into the ground to offset the amounts pumped out. Of those, 21 aquifers have declined, many of them in arid or semi-arid regions. The researchers studied changes in the amounts of water in 37 major aquifers around the world between 20. "There's no way we can keep using these aquifers at the rates that we are without understanding what some of the tipping points are," Richey said in a telephone interview.
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