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Midwinter Dry Spells Amplify Post-Fire Snowpack Decline

Presentation Date
Friday, December 15, 2023 at 8:40am - Friday, December 15, 2023 at 8:50am
MC - 2022-2024- West



Increasing wildfire and declining snowpacks in mountain regions threaten water availability, alter ecosystem function, and negatively impact local and regional economies. We combine satellite-based fire detections from the Moderate Resolution Imaging Spectroradiometer (MODIS) with gridded 4 km snow seasonality classifications to examine fire activity in California's seasonal and ephemeral snow zones. We find a nearly tenfold (9.8x) increase in fire activity during 2020–2021 versus 2001–2019. Accumulation season broadband snow albedo declined 25%–71% at two burned sites (2021 and 2022) according to in-situ data relative to un-burned conditions, with greater declines associated with increased burn severity. By enhancing snowpack susceptibility to melt, both decreased snow albedo and loss of canopy drove midwinter melt during a multi-week dry spell in 2022. Despite similar meteorological conditions in December–February 2013 and 2022–linked to persistent high pressure weather regimes–minimal melt occurred in 2013. Post-fire snowpack differences are confirmed with surface observations from the Snowpack Telemetry Network and satellite measurements from Terra MODIS. With growing geographical overlap between wildfire and snow, our findings suggest California's snowpack is increasingly vulnerable to the compounding effects of dry spells and wildfire. Our work also highlights how this vulnerability includes the accumulation season in addition to the melt season.

Funding Program Area(s)