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Climate Change Could Soak Up California’s Fresh Mountain Water Runoff

The Sierra Nevadas deliver freshwater runoff that could dry up if temperatures continue rising.

Aired 9/2/14 on KPBS News.

A new study suggests rising temperatures could cut into California's water supply.

A new study suggests rising global temperatures could cut into California's water supply by altering high-altitude vegetation.

Water used to irrigate crops in the Central Valley often begins as runoff from the top of Sierra Nevada mountains. It's so cold up there, vegetation can't take root. But with global temperatures rising, that could change.

"Rain or snow comes in, and the vegetation — the forrest — sort of gets the first crack at it," said UC Irvine's Michael Goulden, a co-author of the new study. "And if it uses that water, it never makes it into the river."

New plants creeping to higher altitudes could sponge up more water before it reaches Californians below. That's the prediction laid out in a new study co-authored by Goulden.

"The mechanism we've identified is so simple," Goulden said. He and his colleagues looked at current relationships between elevation and climate, and teased out how that influenced the water cycle.

"We just combined those two things together and used that to directly project what the patterns of evapotranspiration would look like in 2100," Goulden said.

Goulden and his colleagues predict that, in the worst case scenario, Sierra Nevada freshwater runoff could decline more than 25 percent by the century's end.

It's hard to tell exactly what role climate change has played in California's current drought. But Goulden says many climate change factors could affect California's water supply in years to come.

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