A new way of predicting California’s water supply

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The Sierras near Mammoth Lakes. Photo credit: Brian Calvert

“We live next to the ocean, but we also live on the edge of the desert. And without water, the dust will rise up and cover us as though we never existed.” – Chinatown

Gold made California boom. But water kept it going. That’s especially true for Los Angeles, whose never-ending quest for water is a deep part of its history. Much of LA’s water comes from the snow captured each winter in the Sierra Nevada mountains, and the water collected each spring in the state’s vast system of reservoirs. The problem is, we’ve never really known how much is up there. And these days it’s more confusing than ever.

But Dr. Tom Painter, a snow researcher for NASA’s Jet Propulsion Lab, thinks he’s found an answer. Painter’s answer to the water problem is an airplane he calls the Airborne Snow Observatory, and it can measure vast stretches of mountain snow—from the air. The plane is equipped with two very cool, high-tech instruments. One is called a LiDar, which pulses a huge laser across the surface of the mountains, to measure the snow depth. The other is called a spectrometer, and it measures how white and bright the snow is.

Those two measurements, combined with ground surveys of the moisture in the snow, can tell researchers how much water will run out of the mountains, and when. At least that’s the idea. Deep, heavy snow holds more water. Dark snow—depending on coatings from dust and pollution—absorbs more of the sun’s energy and melts faster. “So we know how much sunlight is gonna be absorbed by the surface above that and how fast that’s going to melt down, wall to wall across the Tuolumne River Basin,” Painter said.

The plane will be loaded with data about the snow above the Tuolumne Basin, which feeds water into San Francisco. In the near future, flights like this can be ramped up to cover all of the Sierras, quickly measuring snowmelt for the state.

This will create a brand new method to help California’s water managers know how much water to keep or release from their reservoirs. Painter likened this system to a system of dual bank accounts, one in the mountains, one in the reservoirs—except it’s getting harder and harder to manage them.

For decades, we’ve had ways to measure the snow and its water from the ground. But the information comes from instruments scattered at low elevations—where snow melts first. That leaves a lot of unknowns, especially late in the spring.

At the same time, there’s a lot of pressure on managers to make sure they use the water wisely. And it’s only getting worse. “The temperature patterns are changing,” said Bruce McGurk, a consultant on Painter’s project and a former water manager for the Hetchy Reservoir, the main water supply to San Francisco. “Climate change is having quite an effect on the accuracy of those forecasts. We also see bigger droughts and bigger floods. This record-setting dry season this spring, since January, is an example of how this system keeps changing.”  Measuring the snow pack by air can help them managers plan more effectively.

But why care? Because without the water from the mountains, and the reservoir system that controls it, Los Angeles might still be a village. In the early nineteen hundreds, major engineering and political feats went into bringing water far from the mountains into the growing city.

Richard Atwater, executive director of the Southern California Water Committee, said California, as it keeps growing, is going to need all the water it can get. “Everybody has a water shortage problem of one nature or another, and you gotta really thank our grandparents and our great grandparents for figuring out how to solve that problem, but we still have work to do,” he said.

More growth means more demands on water. Governor Jerry Brown is right now pushing for a major, $14 billion water project in the Sacramento-San Joaquin River Delta—a major source of water for the state—that could potentially catch more runoff coming out of the mountains. Atwater says this is an issue affecting all Californians. “It affects obviously Los Angeles and Southern California down to San Diego, but it really affects communities from Bakersfield to Fresno to San Francisco to Oakland—it affects really the whole state,” he said. “We’re all in it together.”