California Institute for Energy and Environment (CIEE)

Using statistical models, wildfire risks are described as a function of climatic variables such as temperature and precipitation, and of hydrologic variables simulated using temperature and precipitation. Wildfire risks for the GFDL and PCM models and the A2 and B1 emissions scenarios are compared for 2005–2034, 2035–2064, and 2070–2099 against a 1961–1990 reference period to examine climate change scenarios ranging from neutral to lower precipitation and higher temperatures in California and neighboring states. This study considered changes in the wildfire risks for the larger region, for California, and for northern and southern California. Outcomes for the GFDL model runs, which exhibit higher temperatures than the PCM model runs, diverged sharply for different kinds of fire regimes, with increased temperatures promoting greater large fire frequency in wetter, forested areas, via the effects of warmer temperatures on fuel flammability. At the same time, reduced moisture availability due to lower precipitation and higher temperatures led to reduced fire risks in some locations where fuel flammability may be less important than the availability of fine fuels. Property damages due to wildfires were also modeled using the 2000 U.S. Census to describe the location and density of residential structures. Structure values were determined from census property values and empirically derived ratios describing the fraction of property values ascribed to structures and the fraction of structures within a fire perimeter that are, on average, destroyed in a fire. This analysis indicated that the largest changes in property damages under the climate change scenarios occurred in wildland/urban interfaces proximate to major metropolitan areas in coastal southern California, the Bay Area, and in the Sierra foothills northeast of Sacramento.