If you want to know why California is parched, look up into its mountains.
An important snow reserve in the Sierra Nevada mountains that provides water for millions of Californians is at only about 40 percent of its 2014 level—which was one of the driest years on record, a new NASA survey finds.
Using NASA's Airborne Snow Observatory—a specially equipped snow-tracking plane—and data from state and local water authorities, researchers were able to measure the amount of water stored in the snowpack in the Tuolumne River Basin. The results weren't good.
A measurement taken on March 25 found that the snowpack contained about 74,000 acre-feet of water, compared to 179,000 acre-feet at about the same time a year ago, according to NASA's Jet Propulsion Laboratory.
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"It looks from our snow courses and pillows that statewide, we have about half or less of the lowest April 1 snowpack on record," Frank Gehrke, chief of the California Cooperative Snow Surveys, said in a statement.
On Wednesday, Gov. Jerry Brown issued an executive order imposing mandatory state-wide water restrictions for the first time in California history. Precipitation stored as snow over the winter serves as a crucial water source for farms, businesses and people as it melts over warmer months.
Measurements such as those taken by the Airborne Snow Observatory provide important information for scientists and policymakers in the West to decide how to deal with a drought that has now stretched into its fourth year, said Tom Painter, NASA's Airborne Snow Observatory principal investigator.
"For the past century, we've estimated mountain snowpack by looking at just a few pixels of the screen—that is, a few sparse ground measurements in each watershed basin," Painter said in a statement. "During an intense drought like this one, most of the pixels on the screen are blank—that is, they're snow-free.