Sunday, May 02, 2004
Scientists Warn Of Western Drought
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.
Soot is darkening snow and ice, deadening their ability to reflect sunlight, contributing to a near universal melting and causing as much as a quarter of global warming, the National Aeronautic and Space Administration reported in December. The process accelerates each spring, as soot accumulates on the surface of melting snow, making the remaining snow even darker and speeding the melting cycle.
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