Wildfire Impacts for Temperature Index Snowpack Model Parameters

Streamflow derived from snowmelt is a key source of water for communities and agricultural producers in the western U.S. As wildfires become larger and more frequent in the West (due in part to climate change), it is increasingly important to understand their potential impacts on snowpack. Temperature-index models remain widely used to simulate snowpack in post-wildfire assessments due to their low data requirements. However, there is limited information on how the key parameters of such models change due to wildfires. The objectives of this study are to (1) quantify the observed changes in the melt-rate function and the rain-snow temperature threshold due to wildfires and (2) develop methods to adjust the melt-rate function and rain-snow temperature threshold (or Px Temperature) to simulate the potential impacts of wildfires on snowpack. To accomplish these goals, snow water equivalent data from 42 SNOTEL sites that have been impacted by wildfire are used to estimate the changes in the melt-rate functions and Px Temperatures between the pre-and post-wildfire periods. Then, general linear models (GLMs) are developed to estimate the changes in the model parameters based on readily available topographic, climatic, and land cover information. The results indicate that late season melt-rates typically increase after a wildfire for sites in northern and central ecoregions of the western U.S. Px Temperature also changes for many sites, but the direction and magnitude of change is highly variable between sites. Nearly all the GLMs can estimate the observed parameter changes better than simply using the average observed changes. However, substantial variation in the parameter values is not explained by the GLMs.