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New research from USGS and partners examines the growing geographical overlap between wildfire and snow in California, threatening water availability in a state heavily reliant on snowpack to fill its reservoirs.

Chart showing fire detections in California related to snow seasonality
Figure shows (a) annual fire detections subset by snow seasonality (snow zone); (b) snow seasonality classifications for California; (c) all fire detections (2001–2021), colored by snow seasonality classification: blue (seasonal), red (ephemeral), and gray (non-snow zone). Fire detections in seasonal (blue) and ephemeral (red) snow zones during (d) 2001–2019 and (e) 2020–2021.

Snowpack provides about a third of California’s average annual water supply. Snowmelt in spring and summer flows into major reservoirs and supplies water to farms, cities, ecosystems, and hydropower plants. 

The research, led by the Desert Research Institute (DRI) in Reno, Nevada, combined satellite-based wildfire detections with snow seasonality classifications to examine how wildfire affects California's seasonal and ephemeral snow zones. 

They found that California’s wildfire activity in 2020-2021 was nearly tenfold greater than the average over 2001-2019. As increasingly dry conditions allow fires to burn at higher elevations, reaching ephemeral and seasonal snowpack areas, they remove canopy cover and leave behind dark sooty material. This dark soot allows the landscape to absorb more solar radiation, leading to increased snowpack melt in midwinter, which may cause water shortages during the dry season. 

"Our research suggests that California's snowpack is becoming increasingly vulnerable to the compounding effects of dry spells and wildfire," said Amy East, USGS Research Geologist and a co-author of the study. "As snow melts earlier in the season, it can lead to reduced water availability during the dry season, which can have serious consequences for agriculture, wildlife, and communities that depend on this water supply."  

Co-lead author Benjamin Hatchett, an Assistant Professor at DRI, highlights that this work "points to an immediate need to actively manage our snow-covered lands at landscape scales to reduce high severity fire regimes." Given the record Sierra Nevada snowpack this year, "we'll have a grand natural experiment to see how post-fire environments influences spring melt rates of deep middle- and high-elevation snowpacks. This can provide us with insight toward developing creative management strategies and also help prioritize where to implement these approaches." 

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