India's vanishing groundwater
Two new studies suggest that India's aquifers are undergoing rapid depletion due, almost entirely, to water withdrawals for agricultural use. Satellite measurements indicate that the water table is sinking faster than anyone had previously estimated, with potentially dire implications for the 600 million people living regionally — nearly one-tenth of humanity — who rely on it.
From the Nature study press release:
Using satellite data, UC Irvine and NASA hydrologists have found that groundwater beneath northern India has been receding by as much as 1 foot per year over the past decade – and they believe human consumption is almost entirely to blame. More than 109 cubic kilometers (26 cubic miles) of groundwater disappeared from the region's aquifers between 2002 and 2008 – double the capacity of India's largest surface-water reservoir, the Upper Wainganga, and triple that of Lake Mead, the largest manmade reservoir in the U.S.
Surface water percolating down from rain, snow, lakes, and rivers recharges aquifers. Some aquifers contain water that's thousands to millions of years old. (According to New Scientist, the world's oldest aquifer lies beneath the Sahara — rain that fell perhaps 1 million years ago.)
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