YAKIMA — A new study led by a Central Washington University professor reinforces the link between high-intensity wildfires and accelerating snowmelt.
Dr. Susan Kaspari and CWU alumnus Ted Uecker, along with others, found snow melted significantly faster in burned areas in the Central Cascades, with effects lasting at least a decade. The results could help guide future forest management efforts as officials develop water conservation plans in the face of climate change and the region’s declining snowpack.
Scientists focused primarily on an area affected by the 2012 Table Mountain Fire, an intense blaze that burned more than 42,000 acres about 20 miles northwest of Ellensburg. Additional data was collected at six other sites in Central Washington during the spring of 2015 and 2016, including an unburned area near Stevens Pass.
“Definitely what we see is that snowmelt happens earlier after a wildfire,” Kaspari said. “We rely on the natural snowpack to release slowly, and we can slowly collect it in our reservoirs as the snow is melting out in May and June.”
Kaspari and her team concluded the black carbon left by wildfires darkens the surface of snow and increases the absorption of solar energy. Those findings add to previous studies showing burned woody debris causes snow to melt faster.
Data collected at study areas and through Snowpack Telemetry (SNOTEL) sites showed snow disappeared an average of 19 days — plus or minus nine days — faster after a wildfire burned through an area. Those effects decline over time but last at least a decade. The study said its results likely underestimate black carbon’s influence on snow.
Kaspari believes wildfire’s deleterious effects on Washington’s snowpack could be reduced by the forest management practices recommended by the state’s Department of Natural Resources and others, such as thinning and prescribed burns. Those less intense fires would leave less black carbon for snow, and fewer trees that provide protection from the sun would be entirely destroyed by fire.
“The more we can get the forests back to their natural state, the less often it is that we’re going to have these really high-severity fires moving through,” Kaspari said.
The study was published in the Journal of Hydrometeorology. Grants from the U.S. Geological Service, the State of Washington Research Center and the Geological Society of America funded the research, and the Central Washington Graduate Studies summer fellowship offered additional support. Kaspari plans to present the research at the American Geophysical Union’s Fall Meeting in December 2020.
Connecting the dots
Kaspari and other researchers still need more information on other factors to further determine the effects of megafires on snowpack.
She acknowledged it’s difficult to separate out different variables, including natural variability in weather and the loss of forest canopy. Future studies conducted by her students will investigate data from burn areas on a larger scale in Washington, Idaho, Oregon and California, and Kaspari also wants to learn more about the different ways tree species burn.
The Nature Conservancy’s Emily Howe works as part of a team exploring how the thickness of tree cover affects snowpack in the Cascades. She’s hopeful by June 2021 they will have two years worth of data collected by recording ground temperatures and using cameras placed in trees throughout the east slopes of the Cascades, including burn areas.
“It’ll be really cool to see how these data match up with Dr. Kaspari’s,” Howe said. “It’s a little tricky on the front of getting the data processed right now.”
Previous research shows gaps in the canopy can help build up and retain snowpack for up to 12 weeks longer on the west slopes of the Cascades, but in colder regions such as the Rocky Mountains, more closed canopies mean the snowpack melts more slowly. Howe said it’s unknown how that equation works on the east side of the mountains.
If less tree cover means slower snowmelt, the methods for preventing wildfires and slowing down snowmelt would align. But if more gaps in the canopy reduce the snowpack more quickly, then protecting it would be at odds with the state’s forest management plan.
“The key thing to just remember is fire and water are going to be connected,” Howe said. “Knowing which to put first is a question that needs to be answered.”
Snow supplies 75 percent of runoff in the Yakima Basin and accounts for more than 50 percent of precipitation in Washington’s Cascade Range. Declining snowpack throughout the U.S. has been most pronounced in areas such as the Pacific Northwest, where winter temperatures are closest to the freezing point.
Howe said despite some major droughts, the area’s snowpack has benefited from a favorable jet stream direction over the last 20-30 years. But that’s not guaranteed to last, and she’s worried a quick flip could strain the state’s conservation efforts and put the amounts of water allocated to junior rights holders in jeopardy.
“It’s encouraging to see that it’s bad enough now and people are paying attention enough now that we’re actually starting to pay attention to the way we manage and fund” projects, Howe said. “I don’t know that water conservation has gotten there yet in Washington.”