IS WILDFIRE RISK REDUCTION DAMAGING THE WATER SUPPLY?
MELDING FOREST MANAGEMENT PRACTICES WITH HEALTHY SNOWPACK MELT
BY SUSAN DICKERSON-LANGE HEALTH AND WELLNESS FOREST MANAGEMENT
Forest thinning and gap creation are proven tools for reducing wildfire risk. As the climate warms, this practice is growing more common in the United States, particularly in the west. According to the National Interagency Coordination Center (NICC), in the 13 westernmost states, more than 20,000 wildfires burned approximately 5.8 million acres (2.3 million hectares) in 2022 alone.
Well-meaning wildfire reduction efforts can unintentionally affect seasonal snowpack, however, by altering the rate and amount of melting that occurs. This is driving research in the Eastern Cascades region of Washington state to study these impacts and seek solutions that reduce wildfire risk without negatively impacting the snowpack that provides summer soil moisture to forests and feeds lower-elevation water systems in warmer months.
WILDFIRE REDUCTION AND SNOWPACK RELATIONSHIP
Forest thinning and gap creation are designed to improve overall forest health by reducing the risk of wildfires, promoting biodiversity and enhancing the growth and quality of the remaining trees. Forest thinning involves selectively removing trees or vegetation, while gap creation deliberately produces openings in the forest canopy.
These forest-management strategies are generally approved of by a wide spectrum of stakeholders, including environmentalists, government agencies and fire prevention experts.
The effect that these forest management techniques have on the volume and timing of snowpack melt is less studied and understood; this is important because snowpack plays a crucial role in regulating water supply in many regions, especially in mountainous areas. The snowpack serves as a natural reservoir that provides water supply for forests, agriculture, fish, drinking water and hydropower generation during the spring and summer months.
The forest canopy acts as a sort of umbrella, dictating how much snow reaches the ground, and the amount and frequency of sunlight that shines on the snow. As a result, forest-management techniques that decrease the number of trees and create gaps in the canopy could change the volume of melting snow that flows to lower elevations, as well as the timing of water delivery. With so much depending on a reliable, plentiful snowpack runoff, and the warming climate projected to reduce the Eastern Cascades’ snowpack by 50 percent over the next seven decades, understanding the relationship between forest management and snow melt becomes critical to building climate change resilience.
This is the basis of a recent three-year study conducted by researchers from science and engineering firm Natural Systems Design + Coastal Geologic Services, along with The Nature Conservancy and the University of Washington. The study’s results are informing forest-management planning efforts under development by the Washington State Department of Natural Resources.
METHODOLOGY, RESULTS AND CONCLUSIONS
Snow research in different regions of the American West, including maritime sites in Western Washington and Oregon, and sites in the Intermountain West such as Utah, Colorado and New Mexico, report varying levels of snowpack duration and melt acceleration in response to forest-thinning or harvest. Because the Eastern Cascades region represents a transitional zone between maritime and continental climate conditions, this study fills a data gap in characterizing the relationship between forest density and snowpack.
Using time-lapse cameras and temperature sensors, the research team measured snow storage amounts and snowpack melt rates over three years across a range of elevations and forest densities within the Eastern Cascades.
The study’s findings demonstrate that forest-snow relations in this transitional climate zone are a blend of the observed effects in the maritime climate zone to the west and the continental climate zone to the east. The results suggest that forest thinning intended to improve forest health and wildfire risk is unlikely to exacerbate the hydrologic impacts of climate change. However, reducing forest density in this climate zone via thinning or canopy-gap creation may increase overall water balance (i.e., water quantity) to some degree, but has a lesser effect on the timing of water availability.
A key exception was recorded at one lowerelevation, north-facing site where snow storage duration was substantially longer in the forest gap compared to the nearby dense forest. This indicates that the aspect, or topographic direction, that a snowpack location is facing may be a primary driver of how forest thinning influences snow storage magnitude and duration in the transitional climate zone.
In light of these findings, forest thinning and canopy gap creation in north-facing forests may offer the best opportunity for extending snow storage duration and influencing the timing of water availability when implementing forest-management strategies in the Eastern Cascades and similar transitional zones. Collaboration is ongoing with the University of Washington and The Nature Conservancy to further test this idea and extend results to higher elevation forests, and with the Washington State Department of Natural Resources to consider applications of this study.
Susan Dickerson-Lange, PhD, PHG, is principal hydrologist with Natural Systems Design and Coastal Geologic Services (NSD + CGS), a firm with three offices in Washington state that provides river, coastal and basin science, and engineering services. Dickerson-Lange is particularly interested in understanding and quantifying anthropogenic impacts to watersheds and evaluating strategies for restoration and adaptation, and she is the lead author on several publications related to climate change, forest hydrology and geomorphology.
