California’s Sierra Nevada gives the Central Valley more water than we thought

BAKERSFIELD, Calif. – Imagine if the Sierra Nevada were the largest bathroom scale in the world.

According to Donald Argus, a researcher at NASA’s Jet Propulsion Laboratory, the rain that falls on mountain peaks each year is like a giant foot stepping on the scales. But unlike a foot, some of that water stays in the Sierra and seeps down deep.

Argus is the lead author of a new study This shows that more groundwater flows from below the Sierra into the Central Valley aquifers than previously thought. The data could have major implications for water managers.

“We measure how much water is being gained and lost in California,” Argus says.

So what does the Argus bathroom scale – the Sierra – tell us about the water supply? The space agency’s research shows that in the face of drought, the mere presence of the Sierra is slowly helping to replenish flooded aquifers.

“It looks like more water is being added and more water is being discharged for irrigation than we previously thought,” says Argus.

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 replenish faster than expected, thanks to the help of previously untested waters from the Sierra.

“Perhaps each year we have more water to work with than we thought,” says Argus.

While it’s no secret that much of the valley’s water supply comes from snowmelt from the Sierra, Argus says this new research is the first detailed mapping of the flowing water under the iconic mountain range.

To get the grand total, Argus says his team used data from NASA Grace mission – a pair of satellites that measure tiny fluctuations in the Earth’s gravitational field. This allows scientists to use complex mathematics to infer changes in runoff and groundwater across large landmasses like the Sierra.

About 20 million Olympic-sized pools of water flow into the Central Valley each year between snowmelt from the Sierra, rainfall, and other sources.

Of that, about one-tenth flows underground in aquifers, which are underground lakes and rivers that supply groundwater to the San Joaquin Valley. This water has helped the region become the nation’s fruit basket despite a naturally dry climate.

But there’s a catch. It may take decades for the volumes of water NASA researchers recently studied to flow from the mountaintops to underground aquifers deep below the valley.

“It’s not coming to the Central Valley right away,” says Argus. “We believe it will take 10 to 100 years to travel that long distance.”

Meanwhile, certain regions of central California are losing groundwater faster than others. More than two-thirds of depleted groundwater is concentrated in the southern San Joaquin Valley, Argus says.

The data examining the waters below the Sierra is important information. While the Central Valley comprises only 1 percent of the country’s agricultural land, the region produces 40 percent of its fresh fruits and vegetables.

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