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
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…..
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
Historical Wildfire Records in Western US Westerling et al Westerling et al 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
Observations (IMPROVE) GEOS-chem Global CTM OC concentration / μg m OC biob emission / Tg OC concentration / μg m -3 IMPROVE GEOS-chem 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
Predicting climate change impacts on forest fires and Air Quality Calculate emissions archive met fields GEOS-CHEM Global chemistry model CMAQ Regional chemistry model 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
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]
Aggregated ecosystems (similar vegetation / climate) – 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
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
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 How does this impact wildfires? Temperature / o C Rainfall / mm day -1
Observed Predicted Annual area burned All ecosystems show an increase in Area Burned of between 7 and 87% driven by increasing temperature. +49% +87% AB compared to
Annual total W. US Forest Fire Biomass Consumption Observed Predicted Predicted mean biomass consumption for is 50% greater than during mean / Tg yr -1 Observed Predicted Use stochastic placement of wildfires within ecosystem and ecosystem specific fuel loads. +50%
Predicted Organic Carbon concentrations in W. US for A1 scenario CO Jun-Aug mean at IMPROVE sites +20% Summertime OC in predicted to increase by 20-25%. Implications for visibility. Mean summertime visibility degrades from ~13.2dv ( ) to ~13.8dv ( ). OC concentration / μg m -3 But need longer model runs….
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 (over ) resulting in mean summertime OC to increase by 20-25%.