California is already in its third year of drought, and things aren’t looking any sunnier. Two of the state’s main river basins are now more than 11 trillion gallons (42 cubic kilometers or 10 cubic miles) of water below normal seasonal levels, says a team of NASA scientists. In other words, California needs 11 trillion gallons of water to end its drought, which is estimated to have cost the state $2.2 billion in losses this year.
The NASA team uses satellite measurements of the Earth’s changing shape, surface height and gravity fields. Their findings show that since 2011, the Sacramento and San Joaquin river basins shed an average of four trillion gallons of water a year—more water, the scientists say, than California’s 38 million residents use for domestic and municipal needs. Roughly two-thirds of that loss is due to loss of groundwater beneath the state’s Central Valley.
That’s only part of the grim prognosis. The other involves findings from NASA’s Airborne Snow Observatory, which measures snowpack in California’s Sierra Nevada range. Apparently, early 2014 data shows snowpack at only 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,” said Tom Painter, ASO’s principal investigator. “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.” Hotter, drier soil makes it harder to get water from the snow into reservoirs once snows begin again.
A study in July found that the Colorado River Basin—a source of water for 40 million people in seven states—had lost around 17.2 trillion gallons of water between 2004 and 2013.
While the big thunderstorms hitting the state are helpful, they’re not enough to make a real difference. ”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,” said Jay Famiglietti of NASA’s Jet Propulsion Laboratory.
The National Weather Service estimates that most of California will remain gripped by drought until the end of the winter.