Fire danger in the high mountains is intensifying: That’s bad news for humans, treacherous for the environment

• The following year, California’s Dixie Fire became the first on record to burn across the Sierra Nevada’s crest and start down the other side.
• High mountain fires can create a cascade of risks for local ecosystems and for millions of people living farther down the mountains.
• Since cooler, wetter high mountain landscapes rarely burn, vegetation and dead wood can build up, so highland fires tend to be intense and uncontrollable.

Four decades of rising fire risk

• This enabled fire managers to leave fires that move away from human settlements and up mountains to run their course without interference.
• We analyzed fire danger trends in different elevation bands of the Western U.S. mountains from 1979 to 2020.
• 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.
• 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.

Cascading risks for humans downstream

• High-elevation fires can have a significant impact on snow accumulation and meltwater, even long after they have burned out.
• The result of these changes can be spring flooding, and less water later in the summer when communities downstream are counting on it.
• This can trigger mudslides and increase the amount of sediment sent downstream, which in turn can affect water quality and aquatic habitats.

Hazards for climate-stressed species and ecosystems

• Since they don’t burn often, their ecosystems aren’t as fire-adapted as lower-elevation forests, so they may not recover as efficiently or survive repeated fires.
• Wet mountain areas, with their cooler temperatures and higher precipitation, are often peppered with hot spots of biodiversity and provide refuges to various species from the warming climate.
• While the risk is rising fastest in the high mountains, most of the West is now at increasing risk of fires.