California’s Sierra Nevada gives the Central Valley more water than we thought
While it’s no secret that much of the Central Valley’s water supply comes from Sierra Nevada snowmelt, the new research is the first detailed accounting of the water that flows under the iconic mountain range.
BAKERSFIELD, Calif. — Imagine the Sierra Nevada is the world’s largest bathroom scale.
The rain that falls on mountain peaks each year is like a giant foot stepping on the scale, according to Donald Argus, a researcher with NASA’s Jet Propulsion Laboratory. But unlike a foot, some of that water stays in the Sierra, and seeps deep below.
Argus is the lead author on a new study showing that more groundwater from below the Sierra is funneling into the Central Valley’s aquifers than previously thought. The data has potentially big implications for water managers.
“We’re measuring how much water is gained and lost in California,” Argus says.
So what does Argus’ bathroom scale – the Sierra – tell us about the water supply? The space agency’s research shows the Sierra’s mere presence is slowly helping recharge overtapped aquifers in the face of drought.
“It looks like there’s more recharge, and more emptying of water for irrigation than we had previously thought,” Argus says.
In other words: It’s a wash, he says.
And there’s a clear silver lining: If water managers are able to conserve more groundwater, those supplies should recharge more quickly than anticipated thanks to help from the previously unstudied amounts of water coming from the Sierra.
“Perhaps we have more water to work with each year than we thought,” Argus says.
While it’s no secret that much of the Valley’s water supplies comes from Sierra snowmelt, Argus says this new research is the first detailed accounting of the water that flows under the iconic mountain range.
In order to get the total, Argus says, his team used data from NASA’s Grace Mission – a pair of satellites that measure minute variations in the Earth’s gravitational field. This allows scientists using complex mathematics to infer changes in runoff and groundwater over large land masses, such as the Sierra.
About 20 million Olympic-sized swimming pools full of water enter the Central Valley each year between Sierra snowmelt, rainfall and other sources.
Of that total, about a tenth flows under the ground into aquifers, which are underground lakes and rivers that provide groundwater to the San Joaquin Valley. That water has helped the region become the nation’s fruit basket despite a naturally arid climate.
But there’s a catch to all of this. The amounts of water that NASA researchers have recently studied can take decades to flow from the mountain peaks to underground aquifers deep below the Valley.
“It doesn’t get to the Central Valley right away,” Argus says. “We think it takes 10 to 100 years to make that long path.”
In the meantime, certain regions of Central California are losing groundwater more quickly than others. More than two-thirds of depleted groundwater is concentrated in the southern San Joaquin Valley, Argus says.
The data exploring water from below the Sierra is important information. While the Central Valley contains only 1 percent of the nation’s farmland, the region produces 40 percent of its fresh fruits and vegetables.