ECHO SUMMIT, Calif. — Frank Gehrke skied out on an unseasonably warm March day to take the final Sierra Nevada snowpack measurements of the season near this mountain pass south of Lake Tahoe — only to be stopped short by a muddy meadow where usually there would be deep snow.
Something is happening to the snowpack, according to measurements Gehrke has collected for 20 winters as chief of California’s water survey program.
Near-record snows are melting under record-setting early temperatures this year, a harbinger of the Sierra Nevada spring — and of a trend that is bringing vast changes across the West.
The snow that piles up in the Sierra, the Rockies and the Cascades forms an immense frozen reservoir that drives western power turbines, waters crops and cattle, and flows hundreds of miles to thirsty lawns and throats in desert cities like Las Vegas, Phoenix and Albuquerque.
Snowmelt provides roughly 70 percent of the West’s water flow. But the icy trickle is becoming a roar earlier, as spring has creeped into what used to be winter over the last century.
Spring temperatures in the Sierra have increased 2 degrees to 3 degrees since 1950, bringing peak snowmelt two to three weeks earlier and prompting trees and flowers to bud one to three weeks sooner.
Western rivers are seeing their peak runoff five to 10 days sooner than 50 years ago. Glaciers are melting from Alaska through the Cascades and east into Montana. And in the Pacific Northwest, snowpack has dropped by as much as 60 percent over the last four decades.
The trend is consistent with global warming, scientists say, though they’re less sure of the consequences. The Pacific Northwest could become wetter or drier as weather patterns shift; Northern California could develop the desert Santa Ana winds that fed Southern California’s record wildfires last fall — or not.
The uncertainly illustrates that scientists still have too little information to conclude that the trend is more than a regional cycle, said Bonner Cohen, a senior fellow at the National Center for Public Policy Research.
The Northwest, for instance, has had four alternating warm-and-dry and cool-and-wet phases since the mid-1920s. Measurements 50 years ago were during a cold-wet period, so a decline in the snowpack is to be expected, critics say. Researchers respond that they’ve accounted for the patterns.
“Lots of things can happen, and right now it’s way beyond what the computer modelers can even pretend to understand,” said Myron Ebell, director of global warming policy at the Competitive Enterprise Institute.
Global or not, if the warming trend across the West continues as projected, scientists say it means a smaller snowpack no matter if precipitation increases or diminishes.
More moisture will fall as rain instead of snow, endangering some ski resorts as well alpine meadows that will see encroachment from plants and trees that today grow only at lower elevations.