Western wildfires are spreading farther. They’re burning hotter. And now they’re climbing higher.
Between 1984 and 2017, high-elevation fires saw a median altitude increase of more than 250 meters, according to a study published this summer by researchers from McGill University, Boise State University and the University of California, Merced.
In the Middle Rockies, which extend into Wyoming, wildfires are advancing even faster. The flames have soared more than 500 meters — nearly one-third of a mile — upslope since 1984.
Fire activity in the mountaintops has accelerated at a faster rate than in the forests below, the study found. Warmer weather caused by climate change is quickening both snowmelt and evaporation in the mountains, drying out dense forests that used to be too wet to burn.
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“Lower-elevation forest is fire-adapted,” said Mojtaba Sadegh, an associate professor in the civil engineering department at Boise State University and one of the authors of the study. “There is a distance between conifer trees in the low elevations. In the high elevations, trees are dense, they’re close to one another, they’re intertwined.”
Thicker, steeper forests found at higher elevations are especially vulnerable to crown fires, which occur when the flames leave the ground and race through the canopy, according to Sadegh. The tops of trees offer more fuel than the grasses and shrubs on the ground, intensifying wildfires.
Even high-elevation forests burn occasionally, Sadegh said. But as climate change worsens, fires that used to be rare will become more frequent — and more severe. A separate study by researchers at the universities of Montana and Wyoming determined that the 2020 subalpine fire season in the Rocky Mountains was the region’s worst in 2,000 years.
Mountaintops have traditionally served as natural barriers restricting fires’ range. Now, increasingly combustible high-elevation forests mean wildfires can summit mountains and surmount those former boundaries.
“A lot of the people who live in these areas have not observed wildfires in their lifetime,” Sadegh said.
That inexperience, coupled with such regions’ remoteness, escalates the risk in places that already have small populations distributed throughout forested areas. “We have communities that only have maybe one or two ways out,” he said.
Lasting effects of high-elevation wildfires can extend well beyond the burned areas. Mountains’ snowpack serves as a crucial summer water supply for communities below. Climate change is already accelerating snowmelt, and fires make the water run out even earlier.
After wildfires burn away the tree cover, mountain streams warm more quickly, too. Cold-water species, like trout, have struggled to withstand the warming waters and low flows seen in recent years — threats that are exacerbated by fire, Sadegh said.
In the fire-adapted forests found at lower elevations, seasonal burning has a net-positive effect on wildlife, said Ian Tator, terrestrial habitat supervisor for the Wyoming Game and Fish Department. Impacts are more complicated higher up, but some species still thrive after wildfires clear away the foliage.
“Our sheep populations generally do pretty well under those conditions,” he said. “As is always the case, there’s winners and losers, and there are certain species of wildlife that definitely are going to get a benefit from that.”
High-elevation wildfires are a relatively new sign of climate change, Sadegh said. But he expects there to be an increased focus on the fires’ upward spread.
“You’re going to see a lot more studies on this topic,” he said.