DENVER — A series of unusual spring dust storms has left the snowcapped mountains of western Colorado stained brown and red, even a bit pink. The dust is speeding up the runoff to rivers that supply millions of people with water and raising fears of an increasingly arid West.
Twelve dust storms barreled into the southern Rockies from the deserts of Arizona, Utah and New Mexico so far this year. In contrast, four storms hit the mountains all year long in 2003. Eight occurred in each of the last three years.
"This year's been really, really strong," said Jason Neff, a hydrologist at the University of Colorado-Boulder. "Something's been going on, and I don't think we're exactly sure what."
The storms leave a dark film on snow that melts it faster by hastening its absorption of the sun's energy. That, coupled with unseasonably warm temperatures, has sped up the runoff here, swelling rivers to near flood stage, threatening to make reservoirs overflow and fueling fears that there will not be enough water left for late-summer crops.
"It creates a high-pressured game of Twister for water managers," said Thomas Painter, director of the Snow Optics Lab at the University of Utah. "They're having to make decisions quickly to hold on to water or release water."
Painter has found that dust can speed up snowmelt by as much as 35 days -- in other words, snow that would normally disappear by May 15 would instead be gone by April 10.
Ever since European settlement of the West, there has been dust, caused by outside forces breaking the fragile crust that holds undisturbed desert soil in place. Initially, grazing cattle kicked up the dust. Scientists say it is now more likely to be caused by off-road vehicles, mountain bikers or energy exploration. In a study last year, Neff found that the amount of dust in the Rockies is five times greater than before the late 19th century.
"This is really the story of the wholesale transformation of the West," Painter said.
Even without the dust storms, forecasters predict that global warming will reduce the soil quality in the western United States to dust-bowl levels by 2050, said Jayne Belnap, a scientist with the U.S. Geological Survey. The Southwest's temperatures are expected to rise by 10 degrees Celsius by 2100.
"It's just a harbinger of the future," Belnap said of the dust storms. "This is the kind of world we need to imagine we're going to be living in and decide if we can afford this dust."
