Forests are essential to regulating snowmelt. That’s according to the latest study from the University of Washington.
Researchers set out to study fire resilience by putting tried and true ways to keep fires at bay to the test.
One of the ways is forest thinning, a traditional method of wildfire management, practiced by North American Indigenous people for centuries but often dismissed in modern times.
It’s when foresters shred, mulch or burn small trees, scrubs and dense understory brushes, creating small and medium-sized gaps in the crowns. They also remove any plants resistant to fire.
The latest study, published in the Frontiers in Forests and Global Change journal, shows that forest thinning not only protects against wildfires, but also helps conserve water and replenish the existing natural and human-made reservoirs.
“Our research shows that ecological forest management can recover some of the water lost due to overstocked forests and climate change, thus helping to support aquatic ecosystems that are dependent upon snowpack,” said Emily Howe, the study’s second author and an ecologist at the Nature Conservancy of Washington in Seattle.
In numbers, that means an increase in the winter snowpack by 16% to 30%.
What does the study show?
Cassie Lumbrazo, another one of the authors and a research scientist at the University of Washington and the University of Alaska Southeast, noted that ancient anti-wildfire “treatments recovered about 12.3 acre-feet of snow-stored water per 100 acres on north-facing slopes."
That’s “roughly 15 Olympic swimming pools per square kilometer, compared to about 5.1 acre-feet per 100 acres, or about six swimming pools per square kilometer, on south-facing slopes.”
“Here we show that forest treatments used to reduce wildfire risk also help recover snow storage that has been diminished by forest change and a warming climate, with stronger effects on north-facing slopes than on south-facing slopes,” said Lumbrazo.
Wildfires prove to be among the most economically costly natural disasters, and their severity and frequency keep increasing, thanks to climate change.
Between 2014 and 2023, wildfires have caused $106 billion worth of damage. Meanwhile, 10 of the costliest wildfire disasters since 1970 have happened in the U.S.
The Palisades Fire that scorched through 23,000 acres in Los Angeles last year caused more than $53 billion in damage, according to the United Nations Office for Disaster Risk Reduction.
About the study
Researchers chose Cle Elum Ridge in Washington as the site. This forest area is at mid- to high elevation, has drier eastern mountain slopes, and is vulnerable to drought and wildfires.
Like Utah, wildfires in Washington typically happen between July and October, when the snowpack from the winter and the precipitation from the spring dry up.
Over the last century, this protective snowpack layer has declined because of global warming, as the study notes.
For three years, researchers gathered data through light detection and ranging, which creates 3D digital models with laser light, and time-lapse photography across 12 plots of land, each one of them 100 square meters.
These plots, located on the north and south sides of the Cle Elum Ridge, were experimentally thinned through various methods developed after consulting the Tapash Sustainable Forest Collaborative, a group of decision-makers from the Yakama Nation, the Nature Conservancy, the Okanogan Wenatchee Forest Service, the Washington Department of Fish and Wildlife, and the Washington State Department of Natural Resources. Researchers left four additional plots untreated to serve as a comparison.
The results showed a 30% increase in the depth of the snowpacks on the north-side plots and a 16% increase on the south side.
“On north-facing slopes in this part of the Eastern Cascades, forest structure strongly controls how much snow reaches the ground, because tree canopies intercept snowfall, and small gaps allow more snow to accumulate where sunlight is limited,” observed Lumbrazo.
“On south-facing slopes, where snowpacks are shallower and receive more sunlight, solar radiation and ground vegetation seem to play a larger role in how quickly snow melts.”
Less dense overhead tree coverage led to water recovery. And in the face of global warming, this method also promotes “hydrological resilience” by creating “a sustainable supply of clean water.”
The study noted that although national regulations for forest thinning focus on southern slopes, which are more wildfire-prone, northern slopes should also be thinned to maximize snowpacks.
What can Utah learn?
More than three-fourths of the water supply in areas of Utah and Washington is snowmelt dependent.
J. Bradley Washa, an assistant professor of Wildland Fire Science at Utah State University Extension, concurred last year that forest thinning did not increase wildfire danger when implemented properly.
“With smaller trees removed, the risk of fire changing from a surface fire to a running crown fire is reduced,” he wrote for The Park Record in May 2025. “Once fire moves into the treetops, controlling it is challenging, often resulting in all trees being killed.”
He noted that Utah ranked fourth highest in the country for wildfire risk and advised federal, state and local regulators to move beyond fire suppression to manage this high risk.
The Beehive State experienced a historically poor snowpack this year, as Joel Williams, the director of the Utah Division of Water Resources, said in a statement last month.
“We’ll need consistent snowstorms to make up for the snow deficiency we have been experiencing this winter,” Williams said.