One brisk morning this April, Thomas Painter, a snow and water scientist for NASA's Jet Propulsion Laboratory, stood on the tarmac at Mammoth Yosemite Airport, in California’s Sierra Nevada, watching as a Twin Otter taxied down the runway.
The plane powered up and took off into a crisp headwind, beelining northwest toward a stretch of snowy peaks that glowed pink in the morning sun. Painter, who is 47, tan, and Coloradan, gazed at the aircraft a moment longer, then turned toward me and flashed a bright smile. “Now it’s time to nerd out,” he said.
The plane carried a laser and a highly sensitive spectrometer, along with two of Painter’s researchers. They would be running flights back and forth over the Tuolumne River basin all morning and, if the weather held, into the afternoon. At the end of the day, they’d have a ton of data to answer some basic questions about the snowpack in the basin, which feeds San Francisco’s Hetch Hetchy Reservoir. Like, how much water is up there exactly? And when is it coming down?
Without water, you’d have no Silicon Valley, no wine, no Tesla, no Vegas.
This is good stuff to know if you want to water the cities, farms, and fields of the American West. And not just for gardens and golf courses. Without water, you’d have no Silicon Valley, no wine, no Tesla, no Vegas.
The West gets most of its water from moisture captured as snow in its mountains, mainly the Rocky Mountains in Colorado and Wyoming, and the Sierra Nevada in California. Every year the snow melts and swells the rivers, which in turn refill reservoirs big and small that store and distribute water across a vast, overpopulated desert.
Until now, snow has been measured by surveyors on skis and through a system of sensors called snow pillows—flat plates of steel in mountain meadows that weigh the snow as it comes down and send data via satellite to water managers. But these sparsely distributed snow pillows only exist at low elevations, around 7,000 to 8,000 feet, where they are easy to install and maintain. And they tell us little about higher-elevation snowpack, which melts latest in the spring.
“When you think about the size of the Sierra, you’re measuring a football field based on putting a pencil in one place and making a measurement,” said Bruce McGurk, a former water manager for the Hetch Hetchy and a consultant on Painter’s project. “That’s scary. That’s not good statistics.” Every year there’s a lot of head scratching by the folks who open and close the valves on the dams.
The current snow-survey-and-forecast system, in place since the 1960s, is getting harder to rely on, McGurk said. “The temperature patterns are changing. Climate change is having quite an effect on the accuracy of those forecasts. We also see bigger droughts and bigger floods. The record-setting dry season this spring, since January, is an example of how this system keeps changing.”
Painter’s plane, which he calls the “Airborne Snow Observatory,” is equipped with a LIDAR, a thick-beamed laser that rapidly pulses over the snow, pinging back readings that, when compared against baseline data from the pre-snow autumn, give Painter the snow depth, within 10 centimeters of variance. The spectrometer gives him what is called snow albedo, a measure of how reflective the snow is. This will tell him how much of the sun’s energy is absorbed by the snow. The whiter the snow is, the more it reflects that energy. The darker it is, the more it absorbs and the faster it melts. Combine this information with ground measurements of how dense the snow is—how much water it contains—and you can accurately predict what’s in store for spring.
Having that kind of information will help water managers, McGurk said. It will help them hold on to water in droughts and release water in wet periods to prevent floods.
The April flight was an experiment. Painter hopes to start flights over the entire Sierra Nevada and Rocky Mountains soon—because Mother Nature is starting to act like a crazy aunt. While Painter’s plane was in the air, McGurk was in the mountains, measuring the snow at a place called Gin Flat. What he saw up there was worrisome. “Snow is left in mounds here and there, [but] there’s a lot of bare ground,” he told me. “The birds were singing and the frogs were croaking. This April 1 snow survey is supposed to have a lot of snow, the maximum for the year, and instead it looks like it’s May 1.”