Wildfires are burning higher in the West, threatening water supplies

The burned landscape resulting from the Cameron Peak Fire is seen on Sept. 21, 2021 in Larimer County, Colo. (RJ Sangosti/MediaNews Group/The Denver Post via Getty Images)

Two years ago, a wildfire started burning in Colorado’s Arapaho National Forest. Fanned by high winds and parched conditions, the East Troublesome fire raced up the slopes of the Rocky Mountains, at one point crossing over the Continental Divide amid 12,000-foot-tall peaks. It would become the second largest wildfire in state history, and it happened to start on the same October day that another fire to the northeast, the Cameron Peak fire, would be crowned Colorado’s largest ever fire.

Beyond their size, the two massive 2020 blazes represented prime examples of a troubling trend as our atmosphere warms: wildfires are burning at higher altitudes in the major mountain ranges of the West, including in areas that are normally cloaked in deep snows in winter.

Winter snowpack that melts slowly in the spring and summer is a primary water source for the West. And so these trends of more fire at higher elevations and faster melting represent “a major threat to a critical water reservoir for the region,” said Dan McGrath, a Colorado State University scientist.

McGrath, co-author Stephanie Kampf and colleagues at Colorado State used these Colorado fires as a starting point for a study published earlier this week that shows how wildfires are spreading deeper into seasonally snowy zones, speeding up melting in a region already enduring a historic drought.

These maps illustrate the seriousness of the western drought

Sampling snow at different elevations in the burned area from the big Colorado fires of 2020, the authors found that snow melted up to nearly a month earlier in charred areas compared to non-burned forests nearby. They attributed this in part to a dynamic that has been documented in earlier studies — particularly by Portland State University professor Kelly Gleason — where ash and soot from the fire scar blows over snow, darkening it and causing it to absorb more energy and melt quicker.

Using historic wildfire maps and snow records, the authors also found that between 1984 and 2020 wildfires have burned 70 percent of what they call “late snow zones” — areas that don’t typically melt until May or later — in western mountains. More forest burned in 2020 in these areas than in the previous 36 years combined, the authors found.

McGrath noted that snowpack across the western United States has declined by 15 to 30 percent over the past 70 years; while the timing of peak snowpack has shifted earlier in most places and total snow-covered season has decreased by more than two weeks.

The Post talked to McGrath and Kampf, the lead author on the paper in the Proceedings of the National Academy of Sciences, about the West’s dwindling snowpack and why it is so harmful.

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