Using 23 years of satellite data, University of Utah hydrologists studied how dust-darkened snow is hastening runoff and reshaping the future of water in the Southwest.
It matters. A lot.
The Colorado River, often described as the hardest working river in the West, delivers water to 40 million people across the United States and Mexico.
But drought and overuse have left the river in crisis. The need for water in an area of growing population far exceeds what’s available.
Although the headwaters of the Colorado River begin high in the mountains of Colorado, the river itself journeys 1,450 miles through many arid states.
That journey leaves it vulnerable because the snowpack that sustains the river is increasingly subjected to windblown events that accelerate snowmelt and the resulting runoff is compromised.
A University of Utah-led study debuts a powerful remote-sensing dataset that informs the timing and magnitude of snow darkening and the impacts on melt rates across the Colorado Basin. The research is the first to capture how dust affects the broad expanse of headwaters feeding the Colorado River system.
The new study found that dust deposition can speed snowmelt by up to 1 millimeter water-equivalent per hour when the sun is at its peak. In high-dust years, that adds up to 10 millimeters of melt per day that can be directly attributed to the darkening effect.
“It’s not just how much dust gets deposited over a season, but also the timing of dust deposition that matters,” said Patrick Naple, doctoral candidate of geography at the University of Utah and lead author of the study.
“Dust is very effective at speeding up melt because it’s most frequently deposited in the spring when days are getting longer and the sun more intense. Even an extra millimeter per hour can make the snowpack disappear several weeks earlier than without dust deposition.”
What went into the study
The authors analyzed 23 years of daily satellite images to observe patterns of snow darkened by dust deposition during the melt season during April and May from 2001-2023. The findings revealed that dust-driven melting tends to peak earliest and be most intense in the central-southern Rocky Mountains at mid-alpine elevations.
Researchers focused on the amount of the sun‘s energy reflected by a surface, known as albedo. The brighter the surface, the higher the albedo, and the more energy it reflects. The darker the surface, the lower the albedo, and the more energy it absorbs. Across all land cover types, snow naturally has the highest albedo.
The authors developed algorithms that did two things: quantified how dust lowers the albedo for every single pixel of satellite imagery; and calculated how the additional energy absorbed by dust impacted melt rates.
The dust on snow effect also includes what is happening at the drying Great Salt Lake.
The highest snowpack dust concentrations in 13 years at an Alta study site were recorded in 2022, accelerating snowmelt by 17 days — and dry beds at the Great Salt Lake were the chief culprit in terms of the widespread nature of the dust, another University of Utah study stressed.
This latest study, however, is the most comprehensive to date to probe dust impacts across the Colorado River Basin. It is designed to improve forecasting and water allocation for a system under extreme pressure from changing climate and populations.
“The degree of darkening caused by dust has been related to water forecasting errors. The water comes earlier than expected, and this can have real world impacts — for example if the ground is still frozen it’s too early for farmers to use. A reservoir manager can store early snowmelt, but they need the information to plan for that,” said McKenzie Skiles, associate professor at the University of Utah’s School of Environment and Society and the study’s co-lead author. “If we can start to build dust into the snowmelt forecast models, it will make water management decision-making more informed.”
Skiles said there is more work to be done.
“We know from sediment core records that dust deposition in this area skyrocketed following modern settlement of the West. That tells us that the level of dust we see today is directly related to human activity,” said Skiles. “If we could track ongoing land-use changes and surface disturbance in the region, we might have a better shot of predicting large dust events.”
Other authors include Otto Lang of the University of Utah; Karl Rittger and Sebastien Lenard of the University of Colorado, Boulder; Annie Burgess of Montana State University and Thomas Painter of University of California, Los Angeles.
The study was published in Geophysical Research Letters on March 9.
