It will take around 11 trillion gallons of water—about 1.5 times the maximum volume of the largest U.S. reservoir—to recover from California's continuing drought, according to a new analysis of NASA satellite data.
The finding was part of an update on the state's drought made possible by space and airborne measurements and presented by NASA scientists today at the American Geophysical Union meeting in San Francisco. Such data are giving scientists an unprecedented ability to identify key features of droughts, which can be used to inform water management decisions.
A team of scientists from NASA's Jet Propulsion Laboratory in Pasadena, California used data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites to develop the first-ever calculation of this kind—the volume of water required to end an episode of drought.
Earlier this year, at the peak of California's current three-year drought, the team found that water storage in the state's Sacramento and San Joaquin river basins was 11 trillion gallons below normal seasonal levels. Data collected since the launch of GRACE in 2002 shows this deficit has increased steadily.
GRACE data reveal that, since 2011, the Sacramento and San Joaquin river basins decreased in volume by four trillion gallons of water each year. That's more water than California's 38 million residents use each year for domestic and municipal purposes. About two-thirds of the loss is due to depletion of groundwater beneath California's Central Valley.
Early 2014 data from NASA's Airborne Snow Observatory indicate that snowpack in California's Sierra Nevada range was only half of previous estimates.
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. These data enable accurate estimates of how much water will flow out of a basin when the snow melts, which helps guide decision about reservoir filling and water allocation.
New drought maps show groundwater levels across the U.S. Southwest are in the lowest two to 10 percent since 1949. The maps, developed at NASA's Goddard Space Flight Center in Greenbelt, Maryland, combine GRACE data with other satellite observations.
The scientists cautioned that, while the recent California storms have been helpful in replenishing water resources, they aren't nearly enough to end the multi-year drought.
In July, NASA launched its first spacecraft dedicated to studying atmospheric carbon dioxide. The Orbiting Carbon Observatory-2 (OCO-2) is now in the midst of a minimum two-year mission to locate Earth's sources of and storage places for atmospheric carbon dioxide. Soon after launch, NASA began a field campaign with flights over the Arctic to study the effect of sea ice retreat on Arctic climate. The Arctic Radiation IceBridge Sea and Ice Experiment (ARISE) was the space agency’s first Arctic airborne campaign designed to take simultaneous measurements of ice, clouds and the levels of incoming and outgoing radiation, the balance of which determines the degree of climate warming.