Transcript - Atmospheric Chemistry Modeling Group

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
Climate Change
Air Quality
Visibility
GHGs OC / BC
aerosols
CO
Less fires…..
Increasing
Rainfall
Increasing
Temperature
Longer fire
seasons, more
fires….
Climate change and Forest Fires
Area burned and temperature in Canada
Predicted ratio of area burned
in 3 X CO2 compared to preindustrial CO2
[Gillet et al., 2004]
[Flannigan et al., 2005]
Climate impact on fire may be complex and vary regionally
due to changes in temperature and precipitation
Historical Wildfire Records in Western US
Large
increase in
wildfires
after the
mid 1980s.
Westerling et al. 2006
Emissions of OC
Biogenic OC
Large Fire Years
Wildfire OC
Large interannual
variability in wildfire
emissions. How does
this impact
atmospheric OC?
OC concentration / μg m-3
OC concentration / μg m-3
Impact of variability of fires on atmospheric OC
Observations
(IMPROVE)
GEOS-chem
Global CTM
IMPROVE
GEOS-chem
2.0
1.5
1.0
0.1
19801984
GEOS-chem
Climatological fires
Jun-Aug mean at IMPROVE sites W of 100oW
0.2
0.3
OCbiob emission / Tg
Interannual variability
in summertime OC
concentrations driven
by wildfires.
Predicting climate change impacts on forest fires
and Air Quality
GISS general circulation model
1950 Spin-up
Area Burned
Regressions
Predict Area
Burned
2000
changing greenhouse gases (A1 scenario)
2025
2050
2100
MM5
Mesoscale
model
archive met fields
GEOS-CHEM
Global chemistry model
archive
chemistry
Calculate
emissions
2075
archive
met fields
CMAQ
Regional
chemistry model
Predicting forest fire area burned
Observed daily
Temperature, Wind
speed, Rainfall, RH
Area burned
database (1o x 1o)
Canadian Fire
Weather Index
System
Aggregate area
burned to
ecosystem
Stepwise linear regression
between meteorological/forest
moisture variables & area burned
[Flannigan et al. 2005]
Daily forest moisture
parameters
Linear stepwise
regression
Predictors of
Area Burned
Aggregated ecosystems (similar vegetation / climate)
6.7
105.8
3.6
11.6
12.8
151.6
4.8
51.8
17.5
25.4
1980 – 2004 Totals
[Westerling et al., 2002]
Area Burned / 106 acres
Biomass consumed/ Tg
4.5
9.8
Bailey (1994) classification
Pacific North West
and Rocky Mountain
Forests are most
important for biomass
consumption and
regional air quality
Pacific Northwest/Cascade Forests. Annual Area Burned
Observed Area Burned
Predicted Area Burned
Area burned / 106 Ha
Regression against linear area burned
0.5
0.25
1980
May-Oct mean Drought Code
1980
1990
2000
R2=52%
1990
2000
May-Oct mean Temperature
1980
1990
2000
Regressions ‘explains’ 50-57% of variability in annual area
burned in forest ecosystems. Best predictors are often
Temperature or Fuel Moisture Index.
Temperature / oC
Rainfall / mm day-1
Trends in GISS western US mean July Met variables
1995 CO2
A1 Scenario CO2
GISS GCM predicts ~1.8 K
increase in western US July
mean temperature by 2055.
How does this impact wildfires?
Annual area burned 1980-2055
Observed
Predicted
+49%
2045-2054 AB
compared to
1995-2004
+87%
All ecosystems show an increase in Area Burned of
between 7 and 87% driven by increasing temperature.
Annual total W. US Forest
Fire Biomass Consumption
1996-2055
1996-2004 mean / Tg yr-1
Observed 19.15
Predicted 20.67
Observed
Predicted
Use stochastic placement of
wildfires within ecosystem and
ecosystem specific fuel loads.
+50%
Predicted mean biomass consumption for 2045-2054
is 50% greater than during 1996-2004
Predicted Organic Carbon concentrations in W. US for 2046-2050
OC concentration / μg m-3
2046
2047
2048
2049
2050
2046-2050 A1 scenario CO2
1996-2000
Implications for visibility.
Mean summertime visibility
degrades from ~13.2dv (19962004) to ~13.8dv (2046-2050).
+20%
Summertime OC in 2046-2050
predicted to increase by 20-25%.
1996
1997 1998
1999
2000
Jun-Aug mean at IMPROVE sites
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 2045-2055 (over 1995-2004)
resulting in mean summertime OC to increase by 20-25%.