Assessing the Association of Drought to Wildfire in California Using a Regional Climate Model Ensemble

ABSTRACT Severe fire weather in California and the western U.S. has greatly increased in recent years, increasingly affecting communities, ecosystems, and contributing to widespread degradation in air quality, indirectly impacting human health and water quality. Several studies have attributed the increase in western U.S. wildfires to warmer spring and summer temperatures, precipitation deficit, reduced snowpack and earlier spring snowmelt.

In this study, we investigate the importance of drought as a driver of wildfire activity over California using reanalysis data. Specifically, wildfire activity is assessed here by severity (95th percentile of Fire Weather Index; FWI95) and duration (the number of spread days) and evaluated against observed area burned. Several drought indices (e.g. Standardized Precipitation Index, SPI; Palmer Drought Severity Index, PDSI; Standardized Precipitation Evapotranspiration Index, SPEI) are used to understand the relationship between drought and wildfire. The ability of a regional climate model to reproduce the robustness of relationship between wildfire and drought is then investigated using an ensemble of long-term simulations using the Weather Research and Forecasting Model (WRF).