1. Future climate change drives increases in forest fires and summertime Organic Carbon Aerosol concentrations in the Western U.S. Dominick Spracklen, Jennifer Logan, Loretta Mickley, Rokjin Park Shiliang Wu, Rose Yevich Mike Flannigan, Tony Westerling, Dan Jaffe

2. Boreal wildfire and climate OC / BC aerosols GHGs CO Increasing Temperature Increasing Rainfall Air Quality Visibility Climate Change Longer fire seasons, more fires…. Less fires…..

3. Climate change and Forest Fires [Gillet et al., 2004] Climate impact on fire may be complex and vary regionally due to changes in temperature and precipitation [Flannigan et al., 2005] Area burned and temperature in Canada Predicted ratio of area burned in 3 X CO 2 compared to pre- industrial CO 2

4. Historical Wildfire Records in Western US Westerling et al. 2003 Westerling et al. 2006 Frequency of large fires Large increase in wildfires after the mid 1980s. Biogenic OC Wildfire OC Emissions of OC Large interannual variability in wildfire emissions. How does this impact atmospheric OC? Large Fire Years

5. Observations (IMPROVE) GEOS-chem Global CTM OC concentration / μg m -3 1.5 2.0 1980- 1984 OC biob emission / Tg OC concentration / μg m -3 IMPROVE GEOS-chem 1.0 0.10.20.3 Jun-Aug mean at IMPROVE sites W of 100 o W Impact of variability of fires on atmospheric OC Interannual variability in summertime OC concentrations driven by wildfires. GEOS-chem Climatological fires

6. Predicting climate change impacts on forest fires and Air Quality Calculate emissions archive met fields GEOS-CHEM Global chemistry model CMAQ Regional chemistry model 1950 2000 2025 2050 2075 2100 GISS general circulation model Spin-up MM5 Mesoscale model archive chemistry archive met fields changing greenhouse gases (A1 scenario) Predict Area Burned Area Burned Regressions

7. Daily forest moisture parameters Area burned database (1 o x 1 o ) Aggregate area burned to ecosystem Canadian Fire Weather Index System Predictors of Area Burned Linear stepwise regression Observed daily Temperature, Wind speed, Rainfall, RH Predicting forest fire area burned Stepwise linear regression between meteorological/forest moisture variables & area burned [Flannigan et al. 2005]

8. Aggregated ecosystems (similar vegetation / climate) 6.7 105.8 17.5 25.4 3.6 11.6 12.8 151.6 4.8 51.8 4.5 9.8 1980 – 2004 Totals [Westerling et al., 2002] Area Burned / 10 6 acres Biomass consumed/ Tg Pacific North West and Rocky Mountain Forests are most important for biomass consumption and regional air quality Bailey (1994) classification

9. Pacific Northwest/Cascade Forests. Annual Area Burned Observed Area Burned Predicted Area Burned Regression against linear area burned May-Oct mean TemperatureMay-Oct mean Drought Code Regressions ‘explains’ 50-57% of variability in annual area burned in forest ecosystems. Best predictors are often Temperature or Fuel Moisture Index. R 2 =52% Area burned / 10 6 Ha 0.5 0.25 198020001990 198019902000 19901980

10. Trends in GISS western US mean July Met variables 1995 CO 2 A1 Scenario CO 2 GISS GCM predicts ~1.8 K increase in western US July mean temperature by 2055. How does this impact wildfires? Temperature / o C Rainfall / mm day -1

11. Observed Predicted Annual area burned 1980-2055 All ecosystems show an increase in Area Burned of between 7 and 87% driven by increasing temperature. +49% +87% 2045-2054 AB compared to 1995-2004

12. Annual total W. US Forest Fire Biomass Consumption 1996-2055 Observed Predicted Predicted mean biomass consumption for 2045-2054 is 50% greater than during 1996-2004 1996-2004 mean / Tg yr -1 Observed 19.15 Predicted 20.67 Use stochastic placement of wildfires within ecosystem and ecosystem specific fuel loads. +50%

13. Predicted Organic Carbon concentrations in W. US for 2046-2050 19961997199819992000 20462047204820492050 2046-2050 A1 scenario CO 2 1996-2000 Jun-Aug mean at IMPROVE sites +20% Summertime OC in 2046-2050 predicted to increase by 20-25%. Implications for visibility. Mean summertime visibility degrades from ~13.2dv (1996- 2004) to ~13.8dv (2046-2050). OC concentration / μg m -3 But need longer model runs….

14. Conclusions In western US interannual variability in summertime OC is driven by variabilty in fires. Increased fires in western US since the mid 1980s has likely caused increase in summertime OC concentrations. Regressions of annual area burned in western US capture 50-57% of interannual variablity. Temperature and fuel moisture are best predictors. Using GISS GCM output, forest fire emissions of OC predicted to increase by 50% by 2045-2055 (over 1995-2004) resulting in mean summertime OC to increase by 20-25%.