Blue Skies, Brown Turns: Does Dirty Snow Enhance Runoff?

By Eugene Buchanan

It’s an experiment any second-grader could concoct. Sprinkle dirt on a shoebox full of snow, place it in the sun and compare its melt-off rate — and accompanying shoebox saturation — to that of a “clean snow” control group. Eliminating all other intervening variables, the dirtier snow is going to disappear faster.

A study by Boulder, Colorado’s National Snow and Science Data Center and Silverton, Colorado’s Center for Snow & Avalanche Studies recently carried this study from the second grade to a statewide level, with the same result. Citing findings from a three-year study, principle researcher Dr. Thomas Painter, who now heads the University of Utah’s Snow Optics Laboratory, said airborne particles from the Colorado Plateau mix with snow and limit the heat it can reflect. This, in turn, means winters out West are getting shorter, with snowpacks melting as much as a month earlier than previous winters.

“It’s common sense, but nobody had ever looked at how dust affects snowpack and where it was coming from,” says the Snow Center’s Chris Landry. “This was a new investigation of something that hadn’t ever been looked at in depth before.”

The study focused its efforts on the Senator Beck Basin study area in Colorado’s San Juan Mountains, the headwaters of the Animas River and the Rio Grande. Using dust deposition data collected over three years, their model found that high-elevation deposition can shorten snow cover duration by 18 to 35 days. That’s a lot of spring skiing.

Before you stop beating your rugs outside with a broom or whipping up plumes of dust on your mountain bike, don’t worry; next year’s ski season will likely be just the same whether or not you skid out on a turn. Most factors enhancing dust emission come from such disturbances as agriculture and development, whose effects are magnified by drought.

Recreationally, this dust deposition affects everyone from skiers to river runners. But it ripples even farther. Landry’s Center calls mountains, and their seasonal snowpacks, the “water towers of the world.” The western U.S. alone, it maintains, gets as much as 80 percent of its water supply from seasonal mountain snows. Its research shows that globally, more than a billion people depend on snow for their water.

This leads to what’s on the horizon. Painter maintains that if scientists can find some way to clean the snowpack, its duration would increase. The other goal is to educate water managers. “Most people we’ve presented the results to have been pretty excited about it,” said Landry. “It adds a new dimension to what produces snowmelt, and that helps them better understand the early runoff we’ve been getting. The next step is working with various water districts to help them include the presence and absence of snowpack dust into their streamflow forecasting.”