Recent storms across California have been helpful in replenishing severe water shortages but aren’t nearly enough to end the multi-year drought, scientists say.
According to research based on data from a NASA satellite it take about 11 trillion gallons of water — around 1.5 times the maximum volume of the largest reservoir in the United States — to recover from the state’s continuing drought.
The finding is part of a sobering update on California’s drought made possible by space and airborne measurements and presented by NASA scientists.
Such data are giving scientists an unprecedented ability to identify key features of droughts, data that can be used to inform water management decisions.
A team of scientists led by Jay Famiglietti of 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.
At the 2014 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.
“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,” Famiglietti says. “That’s an incredible advance and something that would be impossible using only ground-based observations.”
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 is 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.
New drought maps – developed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, by combining GRACE data with other satellite observations – show groundwater levels across the US southwest are in the lowest two to 10 percent since 1949.
“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,” said Matt Rodell, chief of the Hydrological Sciences Laboratory at Goddard.
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.
“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,” added Famiglietti.