Modeling Postfire Effects on Snow Albedo and Forest Recovery Over a Chronosequence of Burned Forests in the Triple Divide Region of the Rocky Mountains

Abstract

Wildfires impact snow albedo, forest cover, and forest structure and thus snow melt rate and snowpack supply for as long as 15 years following burn. These effects have not been quantified at fine spatial resolutions and long time periods at a watershed scale. I modeled the effects of postfire effects on snow albedo, snow-mass energy balance, and resulting snow-water equivalent (SWE) depth over a long-time scale and at a fine spatial resolution. Using a spatially and temporally distributed snow evolution model called SnowModel, I modeled postfire effects on snow albedo and forest structure over postfire recovery within 8 forest fires between 2000 and 2020 in a region in Northwestern Wyoming. SnowModel does not currently incorporate the effects of postfire effects on snow albedo, forest structure nor the recovery of the postfire effects, so I developed and incorporated postfire snow albedo decay functions from Gleason and Nolin (2016) into SnowModel and developed a 15-year postfire recovery of postfire effects on snow albedo and forest structure parameterization informed by remotely-sensed measurements of surface snow albedo from the MODIS-MOD10A1 dataset. I then compared the parameterized model (postfire albedo) with a base model to quantify changes in peak SWE, snow volume, and snow disappearance date (SDD) due to postfire effects on snow and recovery within the burn regions and at the watershed scale for up to 20 years following fire. To partition the postfire impacts on snow due to forest structure from the albedo impacts, I also parameterized a third model with only forest structure impacts (postfire forest) and compared the results with the postfire albedo model and the base model. My hypothesis was that modeled results would show significant and lasting alterations in peak SWE, total snow volume, and SDD for up to 15 years following fire. Postfire parameterizations caused peak SWE losses of between 2.81% and 31.91% (474K m3 to 12.7M m3) and an average 9.93 to 87.97% reduction in ablation season SWE in the year immediately following fire. Immediately following fire, snow disappearance occurred 33 (SD: 3 days) to 58 days (SD: 9 days) earlier than in the base model. Over recovery, losses in total SWE and peak SWE, and shifts in disappearance date tended to shrink relative to the losses observed immediately following fire, but remained negative throughout. In two fires modeled for the entire 15 year postfire recovery period, the greatest losses in peak SWE did not occur immediately