Ensemble projections of wildfire activity and carbonaceous aerosol concentrations over the western United States in the mid-21st century

Abstract

We estimate future wildfire activity over the western United States during the mid-21st 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 84th 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.

The geographic distribution and economic value of climate change-related ozone health impacts in the United States in 2030

“…Other studies have shown linkages between a warmer climate and increased evaporative emissions from mobile sources (Rubin et al, 2006), increased electricity usage (Mideksa and Kallbekken, 2010), and increased wildfire activity over parts of the United States (Yue et al, 2013), all of which could lead to even greater health impacts from climate than shown here.…”

Impact of anthropogenic climate change on wildfire across western US forests

“…Although numerous studies have projected changes in burned area over the twenty-first century due to ACC, we are unaware of other studies that have attempted to quantify the contribution of ACC to recent forested burned area over the western United States. The near doubling of forested burned area we attribute to ACC exceeds changes in burned area projected by some modeling efforts to occur by the mid-twentyfirst century (29,30), but is proportionally consistent with midtwenty-first century increases in burned area projected by other modeling efforts (17,(31)(32)(33).…”

Drivers of changes in stratospheric and tropospheric ozone between year 2000 and 2100

“…Banerjee et al: Drivers of changes in stratospheric and tropospheric ozone al., 2014). The magnitudes of natural emission sources of tropospheric ozone precursors are also likely to be affected by future changes in climate and land use (Squire et al, 2014) through changes in, for example, wildfire activity (Yue et al, 2013), lightning activity (Grewe, 2009;Banerjee et al, 2014) and the amount of isoprene emitted from vegetation Pacifico et al, 2009).…”