Diagnosing California’s Drought Problems with Data
In the California Sierra Nevada, snow-sample data helps scientists to decide who gets water—and who does not.
About 30 years ago in early spring, Frank Gehrke clicked his boots into his skis and glided over the Sierra snowpack. It was his first year on the California Department of Water Resources’ snow survey team—a boots-on-the-ground operation that does crucial work: collecting data to help resource managers understand the state of local water stocks.
Gehrke spent the next several days traveling across the Kern Plateau, a remote area in the southern Sierra Nevada. He took a 100-mile loop that went through forests of lodgepole pines and open meadows, over the 11,200-foot Cottonwood Pass, and on to Mount Whitney, the highest point in the continental United States. Along the way, he took snow samples to quantify the season’s precipitation.
“That was a relatively dry year,” Gehrke recalls, which made for slow progress. “Sometimes we would ski for 100 yards, then have to take off our skis to scramble through brush and gravel.”
Snow is a vital freshwater reservoir for much of the world, including California. As temperatures warm during the spring, snowmelt feeds the state’s water needs throughout the dry summer months. Drought remains a formidable problem, so the data that the snow surveyors collect becomes all the more important as resource managers are forced to grapple with the realities of limited water reserves.
Today, Gehrke leads these efforts as the state’s chief snow surveyor—and some years, he says, are more challenging than others.
In the Sierra, a Long Tradition of Snow Patrol Data
Snowpack accounts for about 30 percent of the annual water supply that California uses for farming, hydropower and drinking water. The state’s water resources are often scarce and officials’ decisions about how to divvy up those resources require that they understand how much water the snowmelt will yield every year. In years with plentiful snowfall, those decisions might include diverting more of the snowmelt into artificial reservoirs for future years. In dry years, however, it means “allocating who gets water and who doesn’t,” Gehrke says. “And that gets very complex.”
It’s a longstanding challenge that, at the turn of the 20th century, spurred the beginnings of the data-collection work that Gehrke and his team use today. When a water rights dispute broke out in 1906 between a hydropower company and landowners in the Lake Tahoe Basin, a local professor realized that he could measure the water content of the snowpack to predict how much water the melting snow would supply. That information, he reasoned, could help to resolve the conflict.
He invented the Mount Rose sampler, a long tube that scientists used to take a core of snow from various sites in the Sierra Nevada that was then measured and weighed to calculate density. The snow water equivalent (SWE) figure indicates how much water the snowpack holds, measured in inches, and it is still used today. The professor’s contemporaries hailed the need for such a tool, and by the 1920s it had spread throughout the western United States, and even abroad.
Gehrke used a Mount Rose sampler on his first 100-mile march through the Kern “snow course,” one of about 240 snow courses in California that teams of two to three people measure annually between January and May, and the tool is largely unchanged.
From Plastic Tubes to LiDAR, Snow Surveys Get High Tech
The Mount Rose sampler isn’t the only data-gathering tool that the snow surveyors use. Since the 1970s, the team has leveraged a network of snow telemetry (SNOTEL) sensors that estimate water content by taking monthly measurements of the depth and weight of the snow resting on top of them. Recently, one federal program began to experiment with LiDAR, a laser-based detection technology, to estimate water content.
But these high-tech data collection methods are still nascent, and Gehrke emphasizes that samples, taken by hand with a Mount Rose sampler, remain critical.
“If anything, [samples] become even more important,” he says, “as they are used to verify the data collected by high-tech methods—and to fine-tune the accuracy of those programs.”
Whatever the collection method, the snow survey data will be critical to citizens in parched states like California. Research suggests that climate change has increased the likelihood of extreme droughts in The Golden State, and could result in snowpack declines as high as 60 percent over the next 30 years.
The Spring 2018 Results Are In
The Kern River Basin’s snowpack is at just 13 percent of the average for this time of year. Which begs the question: One day, could Gehrke’s snow survey successors be forced to ditch their skis for good?
This content is produced by WIRED Brand Lab in collaboration with Western Digital Corporation.