wildfire activity and carbonaceous aerosol2 concentrations in the western United States3

We investigate the impact of climate change on wildfire activity and car-18 bonaceous aerosol concentrations in the western United States. We regress19 observed area burned onto observed meteorological fields and fire indices from20 the Canadian Fire Weather Index system and find that May-October mean21 temperature and fuel moisture explain 24-57 % of the variance in annual area22 burned in this region. Applying meteorological fields calculated by a general23 circulation model (GCM) to our regression model, we show that increases24 in temperature cause annual mean area burned in the western United States25 to increase by 54 % by the 2050s relative to the present-day. Changes in area26 burned are ecosystem dependent, with the forests of the Pacific Northwest27 and Rocky Mountains experiencing the greatest increases of 78 % and 175%28 respectively. Increased area burned results in near doubling of wildfire car-29 bonaceous aerosol emissions by mid-century. Using a chemical transport model30 driven by meteorology from the same GCM, we calculate that climate change31 will increase summertime organic carbon (OC) aerosol concentrations over3