Fire is becoming an increasingly destructive force in mountain areas. This has many environmental and economic impacts. A new study from the USA investigates how extreme wildfires in 2020 affected the water cycle in key mountain forests that store water in the form of snow pack that is released through spring. The findings are consistent with earlier research in the Australian high country.

Bob Berwyn, writing for Inside Climate News says that the findings of the study, published in September in the Proceedings of the National Academies of Sciences, suggest that the relationships of snow and water in many Western mountain forests are ‘caught in a vicious climate cycle, with more fires leading to faster snowmelt and reduced water, which, in turn, makes forests more flammable’.

The surveys,  at about 10,000 feet in the Rocky Mountains west of Fort Collins in Colorado, were part of a rapid response science assessment to measure just how much the extreme 2020 wildfire season in the West disrupted the water-snow cycle in the critical late-snowmelt zone which serves as a huge natural reservoir. The snowmelt sustains river flows that nurture ecosystems, fills irrigation ditches for crops and delivers supplies of industrial and drinking water to communities.

The critical areas are at different elevations in various parts of the West, depending on latitude and other geographic factors, but long-term wildfire records suggest that for millennia, fire was a rare visitor in many high-altitude forests, with burn intervals of 200 to 300 years, or even longer in wetter regions.

Quoting Stephanie Kampf, a Colorado State University researcher, Bob reports on the difference between burnt and unburnt areas:

“It was just so striking to go up to these places and see no snow left,” she said. In one unburned comparison plot a short distance away, there was still more than three feet of snow. “It’s disturbing when you’re accustomed to a place and how it was, and you see it change that much. It’s kind of mind blowing. I suspected that what we experienced in 2020 was outside the norm, but I didn’t realize how far outside the norm it was. And that was just honestly pretty disturbing.”

Bob writes:

Wildfires are leaving mountains free of snow earlier in the year. He quotes the authors: “this loss of snow can reduce both ecosystem water availability and streamflow generation in a region that relies heavily on mountain snowpack for water supply.” And as the snowpack melts earlier, the ground and plants warm up and dry faster, setting the stage for more fire in a vicious cycle of climatic changes”.

The situation in Australia

Here in Australia, the Alps are the headwaters of most of the significant rivers of the south east. As such, they are incredibly important for their role in supplying water to downstream areas, where it is used for environmental flows, agriculture and human consumption.

Research contained in the report ‘Impact of fire on montane snowpack energy balance in Snow Gum forest stands’ by Andrew Schwartz, Hamish McGowan and Nik Callow found that bushfire affected forests have higher snowpack evaporation, which results in less runoff.

Debris shed by burned trees lowers snow albedo and increases heat emission from decaying tree stems and other organic matter (which is often burnt black by the fire).

They found that an intact canopy cover moderates radiation from the snowpack and that there was ‘reduced snowpack longevity and increased melt’ in bushfire-disturbed forests.

This issue is covered in more detail in the report An Icon at Risk available here.