The Southwest Colorado snowpack has seen five notable layers of dust this winter, each with the capacity to have a big impact on spring runoff.
Little dark specks of dust absorb more solar radiation than the surrounding white snow. With more solar radiation comes increased warming and then waves of snowmelt. Researchers keep an eye on this phenomenon because it can be tied to less water downstream, particularly in the late summer.
“A couple of those events are very noticeable in the snowpack,” said Jeff Derry, executive director for the Center for Snow and Avalanche Studies. “If you can easily see a dust layer in the snowpack, it’s really going to play a big part in affecting snowmelt when it comes to the surface of the snowpack.”
The latest layering of dust, called a dust on snow event, occurred Wednesday – and was buried by a few inches of precipitation afterward. That created a reset, Derry said.
The fresh, white snow will reflect solar radiation back into space and slow the warming and melting of the snowpack – until it melts enough that the dust layer peeks its head to surface again.
“It will absorb more radiation and increase warming and melting,” Derry said.
Mountains are nature’s water tower, and the snowpack is a natural reservoir, he said.
Left to its own devices, the snowpack would melt slowly and steadily, sending water downstream for longer into the summer season.
Southwest Colorado already does not have as much snowpack as it would like. As of Friday, the region’s river basin held 61% of the median historical snow-water equivalent, the amount of liquid water held in snow.
If that slow dripping reservoir melts more quickly because of dust, then soil and plants can start using water earlier in the season through a process called evapotranspiration. That can decrease the water that goes downstream to others in the Colorado River Basin, which supports about 40 million people.
And, it can impact recreation, reservoir management and wildfire conditions.
“Given that a lot of the dust is at-surface or near-surface, and the forecast is a dry, hot spring, my forecast is that we’re going to see a rapid snowmelt,” Derry said.
Around Colorado, the snowpack has warmed 32 degrees, which means melting is on the horizon, Derry said. But that melting could also be delayed.
“If you keep getting snowstorms, which add snowfall and reflectivity, that could delay snowmelt for however long,” he said.