High-resolution wildfire simulations reveal complexity of climate change impacts on projected burn probability for Southern California

Background Wildfire is a major contemporary socio-ecological issue facing the people and natural resources of Southern California, and the prospect that a warming climate could lead to a higher probability of fire in the future is cause for concern. However, connecting climate change to projected burn probability is complex. While most models generally show temperature increasing in the future, changes in humidity and precipitation are less certain, and these changes interact to generate projections of future climates that are sometimes, but not always, more conducive to wildfire. We ran FSim, a stochastic, high-resolution spatial (270 m) and temporal (daily) fire spread model, with projected Energy Release Component (ERC) derived from multiple global climate models (GCMs) under RCP8.5 climate change scenario to explore the impact of a range of future climate trajectories on simulated burn probability and to quantify the uncertainty arising from multiple GCMs. Results We observed considerable uncertainty in the future direction of change for burn probability. Future changes were more certain in the Southern Coast region of California, where 75% of simulations projected an increase in burn probability. In the Central Coast region, five out of eight GCM-based simulations projected increased burn probability. Less than 1% of the total burnable study area had unanimous agreement on the projected direction of change. Simulated changes in burn probability were directly correlated to annual projections of changes in ERC, but were also affected by the seasonality of ERC change, as well as interactions between humidity, precipitation, and temperature. Conclusions The observed variability offers insights into why, and under what climate conditions, burn probability may increase or decrease in the future. Our study is novel in its examination of a wide range of potential future burn probability projections for Southern California using a regional application of a high-resolution stochastic fire spread model, and the complexity that we demonstrated for Southern California suggests that simple correlations of increasing fire with increasing temperature are likely underestimating the range of plausible future fire scenarios.