COLORADO — Colorado's high mountains are an essential water source for human and livestock consumption, fish, aquatic invertebrates, plants, animals and everything else living on our mostly blue planet. Our snow-covered mountains are a reservoir of frozen water that melts and fees our rivers, streams and us.  

This natural process is under threat due to the presence of dust on the snowpack. This dust, often originating from the arid regions of the Southwest, is altering the snow's reflective properties, leading to accelerated melting. As a result, the timing and volume of snowmelt are becoming increasingly unpredictable, posing a significant challenge to water resource management. 

Snow in the mountains and the rate at which it melts have many indirect influences; in high-altitude alpine ecosystems, a faster than normal snowmelt causes an earlier snow-free season which can determine the plants that dominate the tundra ecosystem. The timing of snowmelt is critical in affecting the onset of fire season. Earlier snowmelt and runoff result in decreased discharge of water to streams and reduced water throughout the dry season. 

White snow has a high albedo rate, which is a measure of how much sunlight is reflected by the bright snowpack. Many outdoor enthusiasts have experienced this when they forget to cover or apply sunscreen to the bottoms of their ears or chins. The sunlight is shining from up above, right? Well, yes and no. The rays from the sun are beaming down, and they are also being reflected up from the snow by our feet.  

Dark surfaces like trees and snow with dust have lower reflectivity to the sun and its heat. On dark, dust-covered snow, this solar energy warms the snow and increases the rate and time at which it melts. 

The rate of snowmelt has significant impacts on watersheds and stream flows.  

Rectifying the impacts of dust on snow won't come easy. The dust is a non-point source of pollution, meaning it does not come from a single identifiable source. The sources are numerous and diffuse 

Jeff Derry is the Executive Director of the Silverton-based Center for Snow and Avalanche Studies and researches the impacts of dust on snow in mountains. He explains, "Colorado is downwind of the biggest dust source in the United States, the four Corners, a region where the states of New Mexico, Arizona, Utah, and Colorado meet. More dust becomes airborne out of that region than any other region in the lower 48. In Colorado, a storm track coming up from the Southwest in the winter, can pick up the dust and bring it to Colorado Mountains. Once it hits our mountains, especially the San Juans, they are the first and hardest hit; the storms drop that dust, and it settles on the snowpack. Hopefully, we get more snow to bury it.  

"This year, we have seen pretty few storm tracks come up out of the Southwest, and this is both due to a lack of snow and a lack of dust storms. We've only had one dust storm this season. Usually, we get more dust events in March, April, and May. We are entering the dust season now. The desert is trying out now, and hopefully, we will see more storms during this period, which will pick up dust. 

"In springtime, we see dust layers in the snowpack [from numerous storms]. When that first-top snow layer gets exposed to the sun, it lowers the albedo, and how much is reflected. A clean, shiny, bright, fresh snow reflects up to 90% of solar radiation/heat. In contrast, a dirty, dusty snow surface may have an albedo of 40-50 percent. Half of the solar radiation is being absorbed by the snow and half is being reflected. The solar radiation that is being absorbed is contributing towards melting the snowpack. 

"When that first dust layer is at the surface, this increases the surface solar radiation; this melts the snow faster than it would have otherwise. Then, this snow melts down to the next dust layer and coalesces with another layer of dust. The dust does not run off, it stays at the surface. These combined dust layers really darken the snow surface. This makes the snow earlier and typically, it makes the snow melt faster.  

“This has been shown to melt three to five weeks earlier in the season, exposing plants and soils earlier in the season, evapotranspiration starting earlier, and plants waking up earlier.  

"With climate change in the last 20 years where we have seen very hot and dry spring weather and have affected the evapotranspiration rates as well and with snowpack leaving the landscape earlier and losing water that would otherwise go to streams and rivers going towards the atmosphere.” 

Recently, Derry has been traveling around the state and visiting 11 research plots and said, "We do this field work every March, April, and May. We look at a snow profile and look for dust, and if it is there, we note where it is and how severe it is; we measure how much snow is on top of the dust and when it might come to the surface. We send that information to water managers and others to give them an idea when snowmelt timing and rates. When dust comes to the surface, it increases the amount of snow warming and melting. We can tell them when the streams are going to rise or not. 

"This is a pretty unique season in that we haven't had many dust events, so it is a very minimal dust season so far. That can change in an instant. 

Wolf Creek has a pretty faint layer, which is surprising because Wolf Creek has the most dust, with dust from the Southwest and the Valley. There was a new snowpack of about 18 inches on top of a shallow base. It was shallow for Wolf Creek. Without the new accumulation, it would have been only 3.8' deep, which is very low for this site.”