Impacts of climate change from 2000 to 2050on wildfire activity and carbonaceous aerosolconcentrations in the western United States

摘要

We investigate the impact of climate change on wildfire activity and carbonaceousaerosol concentrations in the western United States. We regress observed area burned ontoobserved meteorological fields and fire indices from the Canadian Fire Weather Indexsystem and find that May–October mean temperature and fuel moisture explain 24-57%of the variance in annual area burned in this region. Applying meteorological fieldscalculated by a general circulation model (GCM) to our regression model, we show thatincreases in temperature cause annual mean area burned in the western United States toincrease by 54% by the 2050s relative to the present day. Changes in area burned areecosystem dependent, with the forests of the Pacific Northwest and Rocky Mountainsexperiencing the greatest increases of 78 and 175%, respectively. Increased area burnedresults in near doubling of wildfire carbonaceous aerosol emissions by midcentury. Usinga chemical transport model driven by meteorology from the same GCM, we calculatethat climate change will increase summertime organic carbon (OC) aerosol concentrationsover the western United States by 40% and elemental carbon (EC) concentrations by 20%from 2000 to 2050. Most of this increase (75% for OC and 95% for EC) is caused bylarger wildfire emissions with the rest caused by changes in meteorology and for OC byincreased monoterpene emissions in a warmer climate. Such an increase in carbonaceousaerosol would have important consequences for western U.S. air quality and visibility.