The snowpack in the Cascade Mountains is smaller and melting nearly a month earlier on average in areas burned by wildfires, according to a study published this month in the American Geophysical Union.
This may mean longer and more severe dry seasons for communities and ecosystems in Oregon that rely on slow, steady melting of mountain snow to meet water needs during the dry summer.
“The fact is that a lot of our water supply comes from melting snow, which is going to be a huge problem in the future,” said Jeremy Giovando, a research civil engineer with the US Army Corps of Engineers, co-author of the study.
Giovando’s team used years of pre- and post-fire data from snow telemetry stations or SNOTEL in the American West to measure the average change in melt date and peak water-snow equivalent. after major fires.
The snow-water equivalent is a measure of the amount of water contained in the snowpack when it melts. The melt date is the day the snow water equivalent at a SNOTEL station reaches zero.
According to the study, SNOTEL stations in the Oregon Cascades experienced some of the most dramatic fluctuations in peak snow water equivalent and melt date after a fire of dozens analyzed in the American West and Alaska.
The results add to a growing body of evidence that the Cascades snowpack is particularly vulnerable to the effects of climate change.
The analysis revealed that the snowpack melted an average of 26 days earlier at SNOTEL stations in the Cascades after burning. The maximum snow-water equivalent was also about 17% lower after a fire. On the eastern slopes of the Cascades, the snowpack was about 36% smaller and melted about 20 days earlier in areas that burned.
“Any type of change is important, but something of this magnitude really makes a difference for water managers and water users and anyone who would depend on this runoff,” Giovando said.
When fire tears through the tree canopy, it exposes the snowpack to more direct sunlight. Charred debris can also fall on the snow, obscuring it and causing it to absorb more sunlight.
Kelly Gleason, assistant professor of ecohydrology at Portland State University, co-author of a similar study in 2021. She said the damaging effects of wildfires on the snowpack can last for years in a burned area and some forests may not grow back to their pre-fire state.
Gleason said that with more data, scientists could put together models that help identify where the snowpack is most vulnerable to fire – especially as fires become more frequent and intense due to climate change. These models could give resource managers a better idea of water availability after fires.
“We have these interactive challenges, these threats going forward with climate change and increasing wildfires,” she said. “I think it’s really important that we understand the process, why it’s happening, how it varies over space and time, and so we can plan for it. So we are not left blind.