Quantifying aspect-dependent snowpack response to high-elevation wildfire in the southern Rocky Mountains
Date
2023
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Abstract
Seasonal snow is a critically important water resource for the western U.S., providing water for human consumption, hydropower, agricultural uses, and sustaining ecological biodiversity. However, due to a changing climate, seasonal snowpacks have declined by ~20% in the last century and the timing of annual runoff is occurring 1–3 weeks earlier than the historical normal. Wildfires are an additional disturbance that are impacting high-elevation seasonal snowpacks at significantly greater rates since 2000. The impacts of increased wildfire altered area introduces considerable water resources challenges due to the ways wildfire directly changes the mass and energy balances of seasonal snowpacks for years to decades following the disturbance. While the impacts of wildfire on seasonal snowpack are increasingly well documented, there is a lack of understanding in how impacts might vary across the complex terrain that characterizes these mountainous environments. Utilizing burn-condition paired automated weather stations, regularly repeated burn-condition and aspect paired snow pits and snow depth transects, and snow depth measurements from time-lapse cameras within the 2020 Cameron Peak burn area during the second winter post-wildfire, I found no significant difference in peak snow water equivalent (SWE) between burned and unburned areas on both north and south aspects. Peak SWE was comparably greater (~100%) on north aspects in both burned and unburned areas. On burned south aspects, peak SWE occurred 22 days prior to burned north and all unburned areas. During the spring melt, snow melted 147% faster on burned south aspects compared to unburned south aspects, while on burned north aspects, melt rates increased by ~60% relative to unburned slopes. The increase in melt rates on burned slopes was the result of energy balance differences, with the median daily net shortwave radiation increasing by 170%, while median daily longwave radiation fell by ~205%. However, the net energy evolved over the winter, with the sign of the daily net energy flipping in late March for both burned and unburned areas. In both instances, the magnitude of the net energy was greater in the burned area throughout the observed period. From late march through snow disappearance at the burned site, the net energy was ~60% greater at the burned site than the unburned weather station. My research provides a more nuanced understanding of wildfire impacts on seasonal snowpacks compared to previous work, as this work identified clear aspect-dependent differences in the response. These findings can be incorporated into physical models so water managers can better predict the timing and quantity of melt from these critical water resources in fire-impacted regions.
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Subject
snow hydrology
snow energy balance
snow-wildfire interactions