When researchers analyzed decades of snowpack monitoring data across western North America, including many in Colorado, they found that snow at more than a third of the stations melted significantly earlier in the year than it did in the mid- to late-20th century.
The new study from the University of Colorado is the first of its kind to look at historical snowmelt data to understand the long-term impacts of a warming world on alpine snowpack, the water storage of the West.
Colorado’s snowpack acts like a drip irrigation system, with the snowpack — and thus water stored as snow — peaking around April 1 each year. As spring brings warming temperatures, snow slowly and steadily melts, first saturating the dry ground, then flowing through rivers and streams to both human and ecological uses.
If the snowmelt begins to drip earlier in the season, there is less runoff to flow on and through the ground during the summer months. Unless precipitation increases — either adding to the snowpack in the winter, or supplementing runoff in the spring and summer — there are fewer water resources during the growing season.
Snowpack declined about 11% during the study period, but earlier winter runoff was roughly three times as widespread, based on data from 1,065 snow telemetry sites. Measures like snowpack can inform resource managers of the current water year’s conditions, Musselman said, while runoff timing is likely more indicative of long-term climatic trends.
“This is one of the first times we’ve been able to put these data together and see that we’re seeing real-time changes in winter snowmelt,” said Keith Musselman, the study’s lead author and a research associate at CU’s Institute of Arctic and Alpine Research.
The study didn’t look at the why of earlier snowmelt, but Musselman said there are some likely culprits. Climate change and warming temperatures can lead to faster melting as well as increase the likelihood of snow to sublimate, or go from solid snow straight to water vapor. Other possible causes for the early runoff, according to Musselman, could include dust settling on top of snow and decreasing its albedo, or reflectivity, which leads to faster melting.
If this all sounds like a bad scenario, it’s because it is. Soils that saturate too early in the year due to winter runoff will act like a sponge full of water, according to Musselman, so they won’t be able to work as a buffer against flash floods as more snow melts or rain falls in spring and summer.
Microbes in dirt also reactivate when runoff returns. As those organisms do the dirty work of breaking down organic matter, they release carbon dioxide, which contributes to climate change. The earlier they get back to work, the more carbon dioxide they emit into the atmosphere.
This winter’s lackluster snowfall means the megadrought across Colorado and much of the West will continue until significant precipitation returns. Musselman said more data is needed to determine the exact impacts of earlier runoff, but there will be implications for how societies manage the liquid of life.
“Our water resource infrastructure in the West is built around snowpack. It’s built around the accumulation in the winter and the melt in spring and summer of the mountain snowpack, and water allocations are based on that infrastructure as well,” Musselman said. “That system is changing.”