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California Still Needs 11 Trillion Gallons of Water

15:44PM Dec 23, 2014

Recent rains in the West have knocked the historically severe drought in California back a couple of steps. But according to a new analysis of NASA satellite data, the state still needs about 11 trillion gallons of water to completely recover from its ongoing drought.

A team of scientists, led by Jay Famiglietti at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., used NASA satellites to develop this one-of-a-kind analysis of water volume needed to alleviate a drought. The team determined that water in the state’s Sacramento and San Joaquin river basins were 11 trillion gallons below normal seasonal levels.

“Spaceborne and airborne measurements of Earth’s changing shape, surface, height and gravity field now allow us to measure and analyze 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,” Famiglietti says. “That’s an incredible advance, and [it’s] something that would be impossible using only ground-based observations.”

Data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites reveal that since 2011, the Sacramento and San Joaquin river basins have decreased in volume by about 4 trillion gallons of water per year. About two-thirds of this loss can be attributed to depletion of groundwater beneath California’s Central Valley.

Related results show that early 2014 data indicate snowpack in California’s Sierra Nevada range was about half of previous estimates.

“The 2014 snowpack was one of the three lowest on record and the worst since 1977, when California’s population was half what it is now,” says Airborne Snow Observatory principal investigator Tom Painter. “Besides resulting in less snow water, the dramatic reduction in snow extent contributes to warming our climate by allowing the ground to absorb more sunlight. This reduces soil moisture, which makes it harder to get water from the snow into reservoirs once it does start snowing again.”

The latest drought maps show groundwater levels across the entire U.S. Southwest are in the lowest 2% to 10% since 1949, says Matt Rodell, chief of the Hydrological Sciences Laboratory at Goddard.

“Integrating GRACE data with other satellite measurements provides a more holistic view of the impact of drought on water availability, including on groundwater resources, which are typically ignored in standard drought indices,” he says.

Bottom line, Famiglietti says – recent rain in California have certainly been helpful in replenishing water resources, but more is needed to end the multiyear 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,” he says.

For more information on GRACE, visit