Wednesday, October 5, 2022
Home SCIENCE Wildfires are burning the western snow

Wildfires are burning the western snow

This article originally appeared on High Country News.

The ground under researcher Stephanie Kampf’s boots was black and burned to a crusty soot in June 2021 as she walked across the burned scar left by the 2020 Cameron Peak Fire. A summer after the fire engulfed more than 200,000 acres ablaze, there was no snow to be found on its footprint, despite being nearly 10,000 feet above sea level, where snow often lingers in Colorado. However, in a nearby group of unburned trees, she noticed the combat, some “nice snow” appeared. “It was really amazing,” she said. “It was so mind-blowing to me.”

According to research published Monday in the journal Proceedings of the National Academy of Scienceswildfires are increasingly disrupting snowpack in the fight against the western US, said lead author and professor of watershed science at Colorado State University Cameron Peak Fire:Colorado’s largest fire to date— inspired his research, because it began so close to the continental divide. That surprised fight. “We started to wonder, is this something that’s happening in other parts of the West?” she said.

Kampf and his team set out to determine if there are more wildfires burning at high altitudes. The answer is unequivocally yes. And the consequences are dramatic: snow in areas burned by wildfires is melting 18 to 24 days earlier than average. Climate change is already causing an increase in the length, frequency and severity of the wildfire season. And snowpack is critical to the health of Western people and ecosystems: According to the Natural Resources Conservation Service (NRCS), it contributes 20% to 90% of surface water used for agriculture, energy production, the habitat of aquatic species and more.

The researchers focused on places where the snow doesn’t fully melt until May or later, called late-melt snow zones. These areas tend to stay cold for a long time in the spring and then melt relatively quickly, often creating large melt pulses in the stream flow. The ground cannot absorb all that snow as it melts simultaneously, and as a result, the water ends up in streams for downstream uses.

The authors found that from 1984 to 2020, 70% of late-melt snowfields experienced a significant increase in wildfire activity. “What this study shows very well is that fires are moving into places that we would consider more resilient because they are cooler and wetter,” said Paul Brooks, a professor who studies mountain hydrology at the University of Utah. Brooks was not involved in the study but reviewed the manuscript. In the areas that retain snow the longest in the Southern Rockies, more area burned in 2020 than in the last 36 years combined. “It’s a shocking difference,” Kampf said. “Seeing that in many different mountain ranges, the trend toward larger fires in snowy areas is really the most important finding.”

Wildfires can affect snow in many ways. Trees generally intercept some snow, but when they lose foliage or die, more snow initially reaches the ground. Sometimes this leads to deeper snow. But then other competing factors take hold. A more exposed snow cover absorbs more solar radiation. Soot and other burned materials fall onto the snow, reducing its ability to reflect sunlight and also promoting faster melting. Open areas are also more vulnerable to being swept away by the wind. “It’s a balancing act, which one of those wins to create the snow conditions you see at the end of the season,” Kampf said.

Lower south-facing slopes and sunny regions are particularly vulnerable to the effect of wildfires on snowpack, as they receive more sunlight and solar energy. So are the areas that see severe fires. There is regional variability: For example, cloudy areas in the Pacific Northwest will likely see different effects in snow cover than areas that see more sun.

The study also found that snow in burned areas contains less water. “Snowwater equivalent peak, where snowpack reaches late in the season, is quite important,” Kampf said. “In a lot of places, it’s going to be really correlated to how much flow there is.”

A shorter snow season, which essentially means a longer summer, can have a cascading effect. “It’s like turning off a drip irrigation system a month early,” Brooks said. Plants could start growing earlier, but could also run out of water as summer progresses or be prone to early frosts. That can make it difficult for forests to recover after a fire.

The researchers’ findings may affect how water is managed in the future. In areas already experiencing drought due to climate change, fires can further exacerbate water shortages. If the snow does not arrive in large pulses due to late melting, and if parched and thirsty soil absorbs moisture, less water is likely to reach streams, rivers and eventually reservoirs. Snowpack surveyors watch with concern. “Wildfires are having a huge, huge impact on how ice melts,” said Erin Whorton, a hydrologist with NRCS’s Idaho Snow Survey.

Downstream water managers may need to prepare for earlier melting that will contribute to reservoirs much sooner than necessary. “The timing is really important,” Brooks said. “The surprising nature of less snow…should give people pause.”


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