There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
We estimate future wildfire activity over the western United States during the mid-21(st)
century (2046-2065), based on results from 15 climate models following the A1B scenario.
We develop fire prediction models by regressing meteorological variables from the
current and previous years together with fire indexes onto observed regional area
burned. The regressions explain 0.25-0.60 of the variance in observed annual area
burned during 1980-2004, depending on the ecoregion. We also parameterize daily area
burned with temperature, precipitation, and relative humidity. This approach explains
~0.5 of the variance in observed area burned over forest ecoregions but shows no predictive
capability in the semi-arid regions of Nevada and California. By applying the meteorological
fields from 15 climate models to our fire prediction models, we quantify the robustness
of our wildfire projections at mid-century. We calculate increases of 24-124% in area
burned using regressions and 63-169% with the parameterization. Our projections are
most robust in the southwestern desert, where all GCMs predict significant (p<0.05)
meteorological changes. For forested ecoregions, more GCMs predict significant increases
in future area burned with the parameterization than with the regressions, because
the latter approach is sensitive to hydrological variables that show large inter-model
variability in the climate projections. The parameterization predicts that the fire
season lengthens by 23 days in the warmer and drier climate at mid-century. Using
a chemical transport model, we find that wildfire emissions will increase summertime
surface organic carbon aerosol over the western United States by 46-70% and black
carbon by 20-27% at midcentury, relative to the present day. The pollution is most
enhanced during extreme episodes: above the 84(th) percentile of concentrations, OC
increases by ~90% and BC by ~50%, while visibility decreases from 130 km to 100 km
in 32 Federal Class 1 areas in Rocky Mountains Forest.