Portland State University researchers announced on April 1 that wildfires are causing faster snowmelt during winter rainstorms in Oregon’s western Cascades. The findings come from a new study led by Kelly Gleason, associate professor of eco-hydro-climatology at PSU’s School of Earth, Environment & Society.
The study is significant because mountain snow acts as a key water source for the Pacific Northwest, supporting reservoirs, municipal and irrigation supplies, hydroelectric power production and habitat during dry months. Rapid melting caused by wildfires could threaten these resources by reducing how long snow can hold water.
According to the research team at PSU’s Snow Hydrology Lab, snow in areas burned by wildfire melted much more quickly than in nearby unburned regions when warm rain fell on existing snowpacks—a phenomenon known as rain-on-snow events. These events can trigger rapid melting and increase flood risk downstream within days. Wildfires open up forest canopies and leave dark debris on the surface of the snow, which increases sunlight absorption and decreases the “cold content”—the ability of the snowpack to absorb heat before melting.
Sage Ebel, lead author of the study and doctoral student at PSU, said: “If a sponge has a lot of space, it can absorb water before anything drains out. But if it’s already saturated, water runs out right away. A snowpack with a lot of cold content can absorb heat before it starts melting. What we’re finding is that small changes in short- and long-wave radiation in the burned sites are keeping that cold content lower than in unburned areas, making them vulnerable to snowmelt during rain-on-snow events.” Ebel added: “The impacts of climate change are exacerbated in the burned forest. There’s less capacity to absorb small changes in warming or inputs from rain than in unburned areas. As the area of burned forests increases with climate change, those effects could have widespread consequences for the water reserves we rely on across the West.”
Researchers installed monitoring stations across various elevations within Oregon’s Breitenbush River watershed—80% of which was affected by wildfire during 2020—and found that between 2023 and 2024 burned sites lost about twice as much snow during rain-on-snow events compared to unburned sites. The greatest impact was seen at mid-elevations where this type of melt accounted for an additional 26% loss over total annual melt compared to unaffected forests.
The researchers say their findings highlight how understanding interactions between wildfires and winter storms is important for improving models used for flood forecasting and future planning around regional water supplies.
The full study appears in Environmental Research Communications.
