Scenarios to Evaluate Long-Term Wildfire Risk in California: New Methods for Considering Links Between Changing Demography, Land Use, and Climate

This paper describes the development and analysis of over 21,000 scenarios for future residential wildfire risk in California on a 1/8‐degree latitude/longitude grid at a monthly time step, using statistical models of wildfire activity and parameterizations of uncertainties related to residential property losses from wildfire. This research explored interactions between medium‐high and low emissions scenarios, three global climate models, six spatially explicit population growth scenarios derived from two growth models, and a range of values for multiple parameters that define vulnerability of properties at risk of loss due to wildfire. These are evaluated over two future time periods relative to a historic baseline. The study also explored the effects of the spatial resolution used for calculating household exposure to wildfire on changes in estimated future property losses. The goal was not to produce one single set of authoritative future risk scenarios, but rather to understand what parameters are important for robustly characterizing effects of climate and growth trajectories on future residential property risks in California. Overall, by end of century, results showed that variation across development scenarios accounts for far more variability in statewide residential wildfire risks than does variation across climate scenarios. However, the most extreme increases in residential fire risks result from the combination of high‐growth/high‐sprawl scenarios with the most extreme climate scenarios considered here. Furthermore, this study shows that the sign of overall statewide risk in the highest growth cases depends on key parameters describing how expected losses vary with increasing housing value at the local level. The paper features case studies for the Bay Area and the Sierra foothills to demonstrate that, while land use decisions can have a profound effect on future residential wildfire risks, the effects of diverse growth and land use strategies vary greatly around the state