Understanding the effects of drought on fire severity in the Sierra Nevada Mountain Range

Keywords: drought, climate, fire severity, tree mortality
Abstract Type: Poster Abstract

Abstract

Fire has caused extensive and dramatic tree mortality across the Sierra Nevada Mountain Range (SNMR), California over the past years, possibly because of acute drought. To understand how drought contributes to tree mortality we need to understand the relationship between climatic variables that create droughts and their relationship with fire severity. This study compares four climate variables that drive drought; 1) average minimum temperature, 2) average maximum temperature, 3) average total summer precipitation, and 4) average total winter precipitation to determine the importance of predictors on fire severity. Fire severity was determined through delta normalized burn ratios (dNBR) for all fires from 1984-2020 in the SNMR. Climactic data was generated using the University of Oregon’s PRISM climate normals data. Analysis was conducted with a dataset with 190 pixels/observations in all fires throughout the SNMR. A generalized additive regression model (GAM) with random effects was fitted to the dNBR index with smooth spline functions of the continuous covariates. Analysis showed that fire severity was significantly higher in areas with the highest summer precipitation (P< 0.0002) and higher in areas with the highest maximum temperatures (P = 0.0131). The results highlight that warmer temperatures associated with drought contribute to high fire severity, but higher summer precipitation also leads to higher fire severity. As the global climate continues to change, understanding the specific climactic conditions that cause tree mortality will be of increasing importance.