Forest Thinning for Fire Risk Simultaneously Boosts Snowpack - by Up to 12 Acre-Feet per 100 Acres
The western United States faces two converging water crises. Wildfires are becoming more frequent and destructive, driven by warming temperatures and drought - the 2025 Los Angeles fires alone caused an estimated $53 billion in damage, topping the list of costliest wildfires since 1970. And snowpack, which provides 53 to 78% of the water for human use across large stretches of Washington and Oregon, has declined over the past century and is projected to decrease by a further 50% by the end of the century as the climate continues to warm.
Forest thinning has been deployed against the first crisis. A study published in Frontiers in Forests and Global Change by researchers at the University of Washington and the University of Alaska Southeast finds, with observational data, that it may also help address the second.
What Forest Thinning Actually Does to Snow
The research focused on Cle Elum Ridge in Washington State - a location that represents mid- to high-elevation forests across the dry eastern Cascades, the Blue Mountains, and parts of the Colville National Forest. These are exactly the forests where wildfire risk is concentrated and where snowpack decline is most consequential for downstream water supply.
Between 2021 and 2023, Dr. Cassie Lumbrazo and colleagues used LiDAR and time-lapse photography to monitor snowpack in 12 plots on either the north or south sides of the ridge, within forest units that had received different levels of thinning treatment. The measurements tracked snow depth and water content through the full accumulation and melt cycle.
The thinning effects on snow storage were substantial, and they varied by slope orientation in ways the researchers had anticipated but could now quantify. On north-facing slopes, which receive less direct sunlight and hold snow longer, forest thinning recovered approximately 12.3 acre-feet of water stored as snow per 100 acres - equivalent to roughly 15 Olympic swimming pools per square kilometer. On south-facing slopes, where sun exposure limits snow accumulation regardless of canopy cover, the effect was about 5.1 acre-feet per 100 acres, or approximately six swimming pools per square kilometer.
"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.
Why Dense Canopies Reduce Snowpack
The mechanism is straightforward but important. In a dense forest, tree canopies intercept falling snow and hold it above the ground, where it evaporates or sublimates before it can accumulate on the forest floor. The canopy also blocks solar radiation that would melt snow - but under dense conditions, the interception effect dominates, reducing total ground-level snow accumulation.
When thinning opens the canopy, more snow reaches the ground and less is intercepted. The reduced canopy density also exposes the snowpack to more variable temperatures, which can affect melt timing in complex ways - but the net effect in this study was a substantial increase in total stored water.
This mechanism is well understood in forest hydrology. What the study adds is rigorous quantification from actual thinned forest units under real-world conditions, linked directly to the kinds of treatments that fire managers are already deploying for other reasons.
The Dual-Benefit Case for Forest Management Investment
The practical implication is significant for how forest management investments are justified and funded. Fire risk reduction is expensive. Thinning operations require equipment, labor, access infrastructure, and ongoing maintenance. Funding streams for this work compete with other priorities and often depend on demonstrating a clear return.
If the same treatments that reduce fire risk also measurably increase water storage in the snowpack - storage that feeds rivers, reservoirs, and aquifers through the dry season - then the benefit calculation changes. Water managers and utilities who depend on snowmelt have a direct interest in supporting forest thinning programs that they might otherwise view as someone else's problem.
The study's observational design - measuring real forests over a two-year period - is a strength, but it also means the findings apply most directly to the specific conditions at Cle Elum Ridge. Whether the same magnitudes hold across different forest types, different treatment methods, or different elevations and climates requires additional research across a broader geographic range.