California will need 42km³ of water to address drought, says Nasa

The US state of California will need more than 42km³ of water to relieve drought conditions and return to normal, NASA estimates.

NASA scientists presented the satellite data findings at the American Geophysical Union meeting in San Francisco.

The estimations were made on the basis of space and airborne measurements through NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites.

The data can be helpful for taking informed water management decisions, the US space agency stated.

The research was carried out at the Jet Propulsion Laboratory (JPL) in Pasadena, California, by a team of scientists led by Jay Famiglietti from NASA.

Famiglietti said: "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."

GRACE data from 2002 to the present has indicated that water deficit had been steadily increasing in the state, with water storage at the Sacramento and San Joaquin river basins in California being 11 trillion gallons lower this year, compared with normal seasonal levels.

Around two-thirds of the loss is caused by groundwater depletion in California’s Central Valley, the agency estimated.

NASA’s Airborne Snow Observatory data from 2014 also indicates that snowpack in California’s Sierra Nevada range has also been reduced by 50%.

NASA Airborne Snow Observatory principal investigator Tom Painter of JPL said: "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.

"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."

However, recent storms in the US state have been helpful for replenishing water resources partially. But those are not sufficient to end the multi-year drought, NASA stated.

Famiglietti added: "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."

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Image: NASA GRACE satellite data showing severity of California’s drought on water resources and trend in water storage between September 2011 and September 2014. Photo: courtesy of NASA JPL.