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.