Examining the impact of changes in climate and vegetation on future fire activity in the Sierra Nevada Mountains, California
Spatial and temporal variability in forest wildfire activity in the Sierra Nevada are associated with variability in natural and anthropogenic ignition sources and vegetation characteristics, climate, and topography. We assembled monthly gridded 1/8 degree historical data describing wildfire occurrence, extent and severity; climate and hydrology; and land surface characteristics (topography and vegetation characteristics). We developed a suite of statistical models simulating fire occurrence, number, extent, and severity as functions of hydroclimate and land surface characteristics. We also used the Fire INventory of NCAR (FINN) with our models and existing vegetation data to simulate wildfire emissions. We then used downscaled projections from a range of global climate models as inputs to our statistical models to simulate changes in future fire activity. Because our statistical models are probabilistic, we can simulate multiple future fire histories for each climate scenario and explore changes in the distributions of extreme events in response to both future climate and fuels management choices.
Large forest wildfire frequency, extent, and severity all increase in the medium term due to warming and greater evapotranspiration. Relatively modest increases in mean fire activity are associated with very substantial increases in the frequency of extreme events, such as large numbers of fires burning simultaneously, large burned area, large high severity burned area, and large emissions in a single fire season. Scenarios for fuels reductions in historically high frequency/low severity forest fire regimes indicate that fuels management may have the potential to greatly reduce wildfire regime sensitivity to changing climate.