11 trillion gallons needed to end California drought, satellite study says
California has experienced rainstorms in recent days but scientists warn that they are not enough to end the drought.
California needs 11 trillion gallons of water to recover from its three-year drought, the US space agency said after studying water resources by using satellite data.
The first-of-its-kind calculation of how much groundwater would end the drought was led by Jay Famiglietti of Nasa's Jet Propulsion Laboratory in Pasadena, California and based on observations from Gravity Recovery and Climate Experiment satellites.
California has experienced rainstorms in recent days but scientists warn that they are not enough to end the drought.
"It takes years to get into a drought of this severity, and it will likely take many more big storms, and years, to crawl out of it," said Famiglietti.
"Spaceborne and airborne measurements of earth's changing shape, surface height and gravity field now allow us to measure and analyse key features of droughts better than ever before, including determining precisely when they begin and end and what their magnitude is at any moment in time.
"That's an incredible advance and something that would be impossible using only ground-based observations."
The more than 40-trillion-litre volume is a huge quantity of water - larger, for example, than the total amount held behind China's Three Gorges Dam.
The entire southwestern United States is far drier than normal, with groundwater levels across the region in the lowest two to 10 per cent since 1949, scientists said.
