Groundwater is disappearing fast from the world and India is among the worst hit, shows data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites.
Among the world's largest groundwater basins, the Indus Basin aquifer of India and Pakistan, which is a source of fresh water for millions of people, is the second-most overstressed with no natural replenishment to offset usage, said two new studies led by the University of California - Irvine (UCI), using data from GRACE satellites.
About a third of the Earth's largest groundwater basins are being rapidly depleted by human consumption, the studies said.
Groundwater aquifers are typically located in soils or deeper rock layers beneath the Earth's surface.
The most overburdened aquifers are in the world's driest areas, where populations draw heavily on underground water. Climate change and population growth are expected to intensify the problem, the researchers warned.
"What happens when a highly stressed aquifer is located in a region with socioeconomic or political tensions that can't supplement declining water supplies fast enough?" asked Alexandra Richey, the lead author on both studies, who conducted the research as a UCI doctoral student.
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"We are trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods," Richey said.
The Arabian Aquifer System, an important water source for more than 60 million people, is the most overstressed in the world, the findings showed.
The studies are the first to comprehensively characterise global groundwater losses with data from space, using readings generated by NASA's twin GRACE satellites.
GRACE measures dips and bumps in the Earth's gravity, which are affected by the mass of water.
In the first paper, researchers found that 13 of the planet's 37 largest aquifers studied between 2003 and 2013 were being depleted while receiving little to no recharge.
Eight were classified as "overstressed", with nearly no natural replenishment to offset usage.
Another five were found to be "extremely" or "highly" stressed, depending upon the level of replenishment in each.
Those aquifers were still being depleted but had some water flowing back into them.
"Given how quickly we are consuming the world's groundwater reserves, we need a coordinated global effort to determine how much is left," principal investigator Jay Famiglietti, who is also the senior water scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, said.
The findings appeared in the journal Water Resources Research.