Environment & Science

Drought: Sierra Nevada runoff could dwindle as planet warms, study says

Snow and water in the Sierra Nevada Mountains.
Snow and water in the Sierra Nevada Mountains.
Photo by Sathish J via Flickr Creative Commons

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A new study found that climate change could mean less freshwater runoff from the Sierra Nevada.

The research suggests that as the planet warms up, more plants will grow at higher elevations, creating denser forests.

By the year 2100, those forests could absorb up 26% of the water that typically runs down the Sierra slopes to feed rivers, lakes and aquifers.

Related: JPL uses GPS data to track Sierra snowpack

Currently, about a third of the state’s water supply comes from melting Sierra Nevada snow.

Michael Goulden, professor of Earth system science at UC Irvine and co-author of the study, said typically that precipitation runs through miles of forested area as it travels down the mountains.

"And you can kind of think of river flow or usable water as what is left over from precipitation after the plants have had a crack at it," Goulden said.

Related: Is the bottled industry shrinking California's water supply?  

Those plants absorb some of that runoff and eventually sweat or “transpire” a good deal of it back into the air.

But Goulden said the Sierras are expected to heat up by four degrees Celsius over the next century.

He argued because of that, more plants will likely grow at higher elevations where before it was too cold for them to survive.

"That denser forest up high will transpire considerably more water and that is going to result in a reduction of the water that’s available for people to use."

A good 'heads up'

Mike Anderson, California’s State Climatologist said this a good first study on the relationship between climate change and Sierra runoff.

But he added that more research needs to be done before the potential effects can be fully understood.

"One thing I have learned about the Sierra is the details mater," Anderson said.

This study looked at transpiration in one area of the mountain range, the Kings River Basin.

Anderson explained that other basins might have physical characteristics that allow them to preserve more or less water over all.

He added that it’s not clear that warmer temperatures will necessarily result in more plants at higher elevations.

"I would treat it as a 'heads up' study," he said. "It's probably something that deserves closer attention in future studies."