We analyzed fire danger trends in different elevation bands of the Western U.S. mountains from 1979 to 2020. Fire danger describes conditions that reflect the potential for a fire to ignite and spread.
Over that 42-year period, rising temperatures and drying trends increased the number of critical fire danger days in every region in the U.S. West. But in the highlands, certain environmental processes, such as earlier snowmelt that allowed the earth to heat up and become drier, intensified the fire danger faster than anywhere else. It was particularly stark in high-elevation forests from about 8,200 to 9,800 feet (2,500-3,000 meters) in elevation, just above the elevation of Aspen, Colorado.
We found that the high-elevation band had gained on average 63 critical fire danger days a year by 2020 compared with 1979. That included 22 days outside the traditional warm season of May to September. In previous research, we found that high-elevation fires had been advancing upslope in the West at about 25 feet (7.6 meters) per year.