The water crisis in the south west of the US is likely to worsen according to a new study carried out by the American space agency and University of California.
Research has found that the Colorado River Basin, the prime source of water in the region, is being sucked dry.
Only last week California announced daily fines of $500 (£300) for residents who water their lawns with nearly four fifths of the state being classified as being under “extreme” and “exceptional” drought conditions.
The Colorado River is the only major river in the southwestern US, with the basin supplying water to 40 million people in seven states and irrigating around four million acres of farmland.
In California, the basin is a key source of water for Los Angeles and San Diego.
The new study is the first to look at the role of groundwater in the parched region and has been carried out against a backdrop of a severe drought dating back to 2000.
A series of monthly measurements have shown that over nine years the Colorado River Basin lost nearly twice as much water as Lake Mead, Nevada – the country’s largest reservoir.
“We don’t know exactly how much groundwater we have left, so we don’t know when we’re going to run out,” said Stephanie Castle, a water resources specialist at the University of California, Irvine.
“This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking.”
Jay Famiglietti, the senior water cycle scientist at the Jet Propulsion Laboratory in Pasadena, warned the findings have long term implications for the entire region.
“The Colorado River Basin is the water lifeline of the western United States,” he said.
“With Lake Mead at its lowest level ever, we wanted to explore whether the basin, like most other regions around the world, was relying on groundwater to make up for the limited surface-water supply.
“We found a surprisingly high and long-term reliance on groundwater to bridge the gap between supply and demand.
“Combined with declining snowpack and population growth, this will likely threaten the long-term ability of the basin to meet its water allocation commitments to the seven basin states and to Mexico.”