A Scary New Number Shows Just How Bad the Drought Is

Researchers find that California's snowpack, which supplies a third of the state's water, is at its lowest level in 500 years.
A snowboarder threads his way through patches of dirt at California's Squaw Valley Ski Resort in March. (Photo: Max Whittaker/Getty Images)
Sep 15, 2015· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

When California officials measured the state’s snowpack in April, they declared it was at the lowest level in 50 years as a four-year drought dragged on.

Turns out they were off by 450 years.

A new analysis published Monday in the journal Nature Climate Change shows that the snowpack, which came in at just 6 percent of average, was at its lowest in five centuries. By late May, the snowpack was gone.

“This record low is unprecedented over 500 years,” said study author Soumaya Belmecheri, a postdoctoral researcher with the University of Arizona’s Laboratory of Tree-Ring Research. “The Sierra Nevada snowpack supplies about 30 percent of water in California—it’s a storage system and a water bank.”

Belmecheri and her colleagues used previously published data from rings in blue oak trees in California’s Central Valley, which serve as a record of the history of rainfall in the region. The trees thrive in dry conditions and grow during winter rains, adding narrow rings in dry years and fat rings in wet years.

Using data from 1,505 trees at 33 sites—a combination of living trees and dead stumps—the researchers compiled a rainfall record stretching back to the year 1300. They combined the rainfall chronology with tree ring data that showed temperature fluctuations to determine the severity of the current four-year-long drought.

Belmecheri pointed out that it’s not just the low rainfall that has scientists concerned but the combination of low precipitation and high temperatures that reduces stores of water in the state’s reserves.

“Temperature is important for the snowpack because it affects the ratio of snow to rain—when it’s warmer, you’re more likely to have rain instead of snow,” she said. High temperatures also accelerate the snowmelt in the spring, leaving little water to flow into reservoirs during the summer when it’s needed most.

In December, scientists from Woods Hole Oceanographic Institution used tree ring data to estimate that the current drought was the worst in 1,200 years.

RELATED: It’s Official: Climate Change Is Making California’s Drought Worse—Much Worse

Researchers from the Lamont-Doherty Earth Observatory in New York have estimated that global warming accounted for 5 to 18 percent of drought conditions in 2014. They found that by the 2060s, more or less permanent drought conditions will set in, with evaporation overpowering short bursts of intense rainfall.

Belmecheri said the snowpack study confirms that conclusion about the impact of climate change.

“We know that the Southwest is very vulnerable to rainfall fluctuations, so when you start having stress over your rainy season, it’s not a simple thing to fix,” she said. “We’ll have to see the adaptive capacity in response to the extreme events like the one California is experiencing.”