Climate change could bring more rain and snow to California

Climate change could bring more rain and snow to California

06 July 2017

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USA –  C limate change could end up producing a chronic El Nino-like weather pattern off the Pacific coast of the United States, leading to a wetter future for most of California, according to a new study.

Without action to rein in emissions of planet-warming carbon dioxide and other gases, the state could see about 12 percent more rain and snow by the end of the century, researchers at the University of California, Riverside, reported today.

That may be good news for California, an agricultural powerhouse with nearly 40 million thirsty people that’s just emerging from a five-year drought. But the findings differ considerably from other projections, which point toward a drier future for the state — and Robert Allen, the study’s co-author, called that a surprise.

Allen, a climate dynamicist and associate professor at UC Riverside, said the study used a newer computer model and relied more heavily on other models that have a better record of simulating precipitation and the effects of an El Nino on the state. El Nino is a cyclical warming of the Pacific Ocean near Earth’s equator, which typically produces warmer temperatures across much of the United States and more rainfall over California.

 Allen said his research points to a “a kind of permanent, El Nino-type situation” that’s likely to lead to more warm, wet winters in California. But it’s the result of warmer air, rather than warmer water.

“The atmospheric response is El Nino-like, even when the sea surface temperature is not,” he said. And while the projection still has a degree of uncertainty, he said the indications of increased precipitation are “pretty robust.”

“On a larger scale, the models robustly project an increase in precipitation for the tropics, a decrease in precipitation in the subtropics and an increase for the northern, poleward side of the mid-latitudes as well as the higher latitudes,” Allen said. “California kind of lies in the middle of the subtropics and the mid-latitudes, which is one of the reasons why California projections are uncertain.”

 The extra precipitation won’t be distributed evenly, Allen said. Already-arid Southern California would see about 3 percent less rain, while the central and northern parts of the state will see 14 to 15 percent more.

The state sees the most precipitation in the winter months of December, January, and February, and it depends largely on mountain snowpack to supply fresh water for the rest of the year. The extra precipitation Allen’s study foresees would fall largely during the same period.

This year’s wet, stormy winter largely broke the back of the recent drought, which may have been California’s worst in centuries. Only a small portion of the state remains dry now. But in the long run, previous studies project that California will see less of a winter snowpack, while more precipitation falling as rain instead of snow means less may be captured in reservoirs for use in the summers.

Allen said the study didn’t examine how much of that additional precipitation would be retained in the mountains, and one study isn’t enough to make public policy decisions. He said he hopes to run a follow-up study with new climate models that are expected to come out next year, “to see if they continue to show the same response.”

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