“Intensifying Fire Hazard in High Mountains Pose a Threat to Humans and the Environment”

As the risk of wildfires rises in the west, firefighters and officials are keeping a closer eye on the high mountains – regions once considered too wet to burn.

The growing fire risk in these areas became startlingly apparent in 2020, when Colorado’s East tricky fire burned and across the Continental Divide to become the second largest fire on record. The following year, California Dixie Fire became the first recorded to burn across the top of the Sierra Nevada and start on the other side.

We study wildfire behavior as climate scientists And engineers. In a new studylet’s see that fire risk has increased in every region in the west over the past four decades, but the strongest upward trends are at high altitudes.

High mountain fires can create a cascade of risks to local ecosystems and to millions of people who live further up the mountain.

Since cooler, wetter high mountain landscapes rarely burn, vegetation and dead wood can accumulate highland fires are often intense and uncontrollable. They can affect everything from the water quality and timing of meltwater that communities and farmers rely on, to erosion that can create debris and mudslides. Ultimately, they can change the hydrology, ecology and geomorphology of the highlands, with complex feedback loops that can transform mountain landscapes and compromise human safety.

Four decades of increasing fire risk

Historically, higher humidity levels and lower temperatures formed a flammability barrier in the highlands. This enabled firefighters to keep fires moving away from human settlements and mountains unimpeded. Fire would hit the flammability barrier and burn through.

However, our findings show that this is no longer reliable as the climate warms.

We trends in fire risk analysed in different elevation bands of the western US mountains from 1979 to 2020. Fire hazard describes conditions that chance of fire to ignite and spread.

In that period of 42 years rising temperatures and drying trends increased the number of critical fire days in every region in the western US. But in the highlands, certain environmental processes, such as previous snowmelt allowing the earth to warm and become drier increased the fire risk faster than anywhere else. It was particularly stark in high elevation forests about 8,200 to 9,800 feet (2,500-3,000 meters) in elevation, just above the elevation of Aspen, Colorado.

We found that by 2020, the high-altitude belt had gained an average of 63 days of critical fire risk per year compared to 1979. That included 22 days outside of the traditional May-September warm season. In previous research, we found that high-altitude fires had progressed upwards in the west about 25 feet (7.6 meters) per year.

Cascading risks to people downstream

are mountains water towers of the world provided 70% of the runoff is those cities in the west rely on. They support millions of people living downstream.

High-altitude fires can have a significant impact on snow accumulation and meltwater, even long after they burn out.

For example, fires remove vegetation cover and tree crowns, which is possible shorten the amount of time the snowpack remains frozen before melting. Soot from fires also darkens the snow surface, increasing its ability to absorb the sun’s energy, facilitating melting. Similarly, a darkened land surface increases the absorption of solar radiation and increases soil temperature after fires.

The result of these changes could be flooding in the spring and less water later in the summer, when communities downstream count on it.

Tree loss caused by fire also removes anchor points for the snow pack, increasing the number the frequency and severity of avalanches.

Frequent fires in upland areas can also significantly affect the sediment dynamics of mountain streams. Due to the loss of the canopy, the rain falls on the ground at a higher speed, causing the chance of erosion. This can cause mudslides and the amount of sediment sent downstream, which in turn can affect water quality and aquatic habitats.

Erosion linked to runoff after fire damage can also deepen streams so that excess water from storms cannot spread into upland meadows and replenish groundwater; instead, they quickly divert water downstream and cause flooding.

Threats to climate-stressed species and ecosystems

The highlands generally have long fire return intervals, burning once every few decades, if not centuries. Because they burn infrequently, their ecosystems are not as adapted to fire as forests at lower elevations, so they may not recover as efficiently or survive repeated fires.

Studies show that more frequent fires could change the type of trees that grow in the highlands or even convert them into shrubs or grasses.

Wet mountain regions, with their cooler temperatures and higher precipitation, are often peppered with biodiversity hotspots and provide refuges for several species from the warming climate. If these areas lose their treetops, species with small distribution areas that depend on cold-water mountain streams can face existential risks if more energy from the sun heats stream water in the absence of tree shade.

While the risk is increasing fastest in the high mountains, most of the West is now at increasing risk of fires. With continued greenhouse gas emissions fueling global warming, this trend of increasing fire risk is expected to continue, putting pressure on firefighting resources as crews fight more fires.