Impacts of Wildfire Activity over Western United States under Changing Climate

Wildfire activity is strongly influenced by climate/weather, fuel, ignition agents and human activities. Weather is the most important factor to affect the wildfire activity when fuel is available. Observational and numerical studies have shown human-induced climate change leads to an increasing trend of wildfire activity and severity in western US and Canada. Warmer and drier climate is favorable for the occurrence of wildfire activities, which could cause the increase of smoke aerosol and worse air quality. This study investigates the impact of changing climate on biomass burning emission over western US by building a linear stepwise regression model among meteorological fields, Canadian Fire Weather Index (FWI), and biomass burning emission. The meteorological fields are taken from time-slice High Resolution Atmospheric Model (HiRAM) simulations for current climate conditions (2010-2015) and future climate conditions (2095-2100, under the Representative Concentration Pathway (RCP) 8.5 scenario). The meteorological fields are further used to calculate the FWI to characterize wildfire activity. The biomass burning emission data is from the Quick Fire Emissions Dataset (QFED) in the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis, which is compiled from satellite-observed fire radiative power and fire locations. The linear regression model built in this study can explain 22-65% of the variance in monthly biomass burning emission over western US and shows the projected biomass burning emission will increase about 2-3 times over regions of Great Basin, Northern Rocky, and Rocky Mountain. The increased smoke aerosols will not only worsen the air quality locally and downwind, but also influence the meteorology. By comparing two periods with high and low smoke aerosol loading, the impact of smoke aerosols on surface irradiance and cloud fraction is investigated. The results highlight the potential increase of wildfire activity in extreme fire weather and could contribute toward improving fire weather predictions and mitigating fire prevention policy.