California’s Historic Drought Is Now Officially Even More Historic

It’s been at least half a millennium since California has been this dry.

The snow in the Sierra Nevada mountains — which provides nearly a third of the state’s water supply — is the lowest it has been in 500 years, according to a new study published in Nature Climate Change.

The researchers compared blue oak tree rings during known time periods of precipitation, snowpack, and temperatures — beginning in 1930 — and found that the data accurately reflected snowpack levels. They then looked at rings going back 500 years to chart California’s historic snowpack supply. The findings revealed the “exceptional character” of California’s ongoing, four-year drought. As of April 1, 2015, the Sierra Nevada snowpack was only 5 percent its historical average, the researchers found.

It’s not that California has never had this little rain, explained Soumaya Belmecheri, lead author of the study and a post-doctoral research associate at the Laboratory of Tree-Ring Research. It’s that the high temperatures have combined with the drought to reduce snowpack. “What is different is the record high temperatures that exacerbated or made this drought more severe,” Belmecheri said.

High temperatures affect the quality of precipitation — whether water falls as snow or rain — and whether the snowpack has a chance to stick around. “The snowpack is like a reservoir. It’s a water bank,” Belmecheri said. “If this kind of drought in California is expected to become more common in the future, you can imagine all the impacts it will have for water in California.”

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