11 trillion gallons of water needed to end California drought, NASA data suggests

Chuck Bednar for redOrbit.com – Your Universe Online
Researchers from the University of Minnesota and Woods Hole Oceanographic Institute (WHOI) have called it the worst drought in 1,200 years, and now NASA researchers have put a staggering number to the amount of water it will take California to fully recover.
In total, the state needs approximately 11 trillion gallons (42 cubic kilometers) of water, or about 1.5 times the maximum volume of the largest reservoir in America, to completely rebound from its ongoing dry spell, Jay Famiglietti of NASA’s Jet Propulsion Laboratory (JPL) and his colleagues reported this week at an American Geophysical Union meeting in San Francisco.

That discovery was part of “a sobering update on the state’s drought made possible by space and airborne measurements,” the US space agency said in a statement Tuesday. “Such data are giving scientists an unprecedented ability to identify key features of droughts, and can be used to inform water management decisions.”
Famiglietti and his fellow NASA scientists used data collected by the Gravity Recovery and Climate Experiment (GRACE) satellites to calculate for the first time the volume of water required to end an ongoing drought episode. Earlier this year, the researchers found that the state’s three-year drought had caused water storage levels in the Sacramento and San Joaquin river basins to fall 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 said. “That’s an incredible advance and something that would be impossible using only ground-based observations.”
Data collected since GRACE launched in 2002 indicate that the deficit has been slowly increasing, and the satellites’ observations indicate that both river basins have decreased in volume by four trillion gallons (15 cubic kilometers) of water each year.
That represents more H2O than the entire 38 million person population of the state use for domestic and municipal purposes each year, NASA noted. Roughly two-thirds of that amount is due to the depletion of groundwater beneath California’s Central Valley, the agency added.
In related findings, early 2014 data from NASA’s Airborne Snow Observatory indicate that the snowpack in California’s Sierra Nevada mountain range was only half of previous estimates. The observatory is also providing the first-ever high-resolution observations of the water volume of snow in the Tuolumne River, Merced, Kings and Lakes basins of the Sierra Nevada, as well as in the Uncompahgre watershed in the Upper Colorado River Basin.
“To develop these calculations, the observatory measures how much water is in the snowpack and how much sunlight the snow absorbs, which influences how fast the snow melts,” NASA explained. “These data enable accurate estimates of how much water will flow out of a basin when the snow melts, which helps guide decisions about reservoir filling and water allocation.”
“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,” added 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 problem is not limited to California either, as new drought maps indicate that groundwater levels are in the lowest two to 10 percent since 1949 throughout the entire southwestern US. Those maps were developed by scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, using GRACE data along with observations from other orbiting probes.
“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,” explained Matt Rodell, chief of the Hydrological Sciences Laboratory at Goddard.
The unfortunate conclusion of this research is the fact that the recent storms in California may have helped replenish the state’s water sources somewhat, but they are far from enough to bring the ongoing drought to an end. Famiglietti said that it will likely take several years, and many more large-scale storms, in order for California to emerge from a drought of this severity.
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