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Water loss caused Sierra Nevada to grow an inch during California drought, researchers say

Water loss caused Sierra Nevada to grow an inch during California drought, researchers say
The Sierra Nevada range rose almost an inch during California's recent drought due to loss of water from within fractured rocks. (Courtesy of Jet Propulsion Laboratory)

The Sierra Nevada grew nearly an inch taller during the recent drought and shrank by half an inch when water and snow returned to the area, according to new research from NASA's Jet Propulsion Laboratory in La Cañada Flintridge.

Researchers used 1,300 GPS stations throughout the mountain range to closely observe how its elevation changed during the drought. They used the differences in height to estimate that 10.8 cubic miles of water were lost from the mountains between October 2011 and October 2015, enough to supply Los Angeles with water for 45 years.

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"This suggests that the solid earth has a greater capacity to store water than previously thought," said Donald Argus, a JPL research scientist.

Water sits atop solid earth like weight on a bathroom scale, Argus said. Mountains give way slightly when snow, water and other precipitation accumulate on the surface, shrinking in height. When the water is taken away, like during California's recent drought, the mountains lose water weight, and grow.

As drought conditions sapped the Sierra of water between October 2011 and October 2015, the mountain range rose 24 millimeters, or nearly an inch. Since October 2015, the Sierra has regained about half of the water lost during the drought and shrank a half-inch.

Researchers knew that the Sierra sometimes grew or shrank, but they believed the differences in height were due to tectonic movements or because the earth rebounds when there is extensive groundwater pumping.

The role of mountains as storage in water systems has been "woefully underexplored in some respects," said Jay Famiglietti, a senior water scientist at JPL and a co-author of the study. Scientists often think of aquifers as primarily layered, sedimentary rock, the type in which groundwater is stored, Famiglietti said.

Mountain water is a potential source of water that could be tapped to quench rising water demand, Famiglietti said. Understanding mountain water could also help researchers better track the replenishment rate of rivers that originate in mountains and provide a more complete accounting of how water leaves and enters natural environments.

"One of the major unknowns in mountain hydrology was what happens below the soil. How much snowmelt percolates through fractured rock straight downward into the core of the mountain?" Famiglietti said.

The ability to estimate mountain water by observing changes in mountain elevations will help researchers better understand that.

But mountain water is highly inaccessible, Famiglietti said. The next step is to find the pathways that mountain water takes.

"It's an important problem in mountain hydrology, but it's especially important in regions like California that need to account for every drop," Famiglietti said.

Twitter: @frankshyong

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