Future climate change drives increases in forest fires and summertime Organic Carbon Aerosol concent

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
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Boreal wildfire and climate
Climate Change
Air Quality
Visibility
OC / BC aerosols
GHGs CO
Longer fire seasons, more fires.
Less fires..
Increasing Temperature
Increasing Rainfall
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Climate change and Forest Fires
Predicted ratio of area burned in 3 X CO2
compared to pre-industrial CO2
Area burned and temperature in Canada
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
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Historical Wildfire Records in Western US
Large increase in wildfires after the mid 1980s.
Frequency of large fires
Westerling et al. 2006
Westerling et al. 2003
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Impact of variability of fires on atmospheric OC
Observations (IMPROVE)
GEOS-chem Global CTM
OC concentration / µg m-3
Interannual variability in summertime OC
concentrations driven by wildfires.
Jun-Aug mean at IMPROVE sites W of 100oW
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Predicting climate change impacts on forest fires
and Air Quality
changing greenhouse gases (A1 scenario)
GISS general circulation model
1950 2000 2025
2050 2075
2100
Spin-up
Area Burned Regressions
MM5 Mesoscale model
archive met fields
Predict Area Burned
GEOS-CHEM Global chemistry model
archive met fields
archive chemistry
CMAQ Regional chemistry model
Calculate emissions
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Predicting forest fire area burned
Canadian Fire Weather Index System
Observed daily Temperature, Wind speed, Rainfall,
RH
Daily forest moisture parameters
Aggregate area burned to ecosystem
Linear stepwise regression
Area burned database (1o x 1o)
Predictors of Area Burned
Stepwise linear regression between
meteorological/forest moisture variables area
burned
Flannigan et al. 2005
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Aggregated ecosystems (similar vegetation /
climate)
12.8 151.6
4.8 51.8
6.7 105.8
1980 2004 Totals Westerling et al., 2002 Ar
ea Burned / 106 acres
Biomass consumed/ Tg
17.5 25.4
3.6 11.6
4.5 9.8
Pacific North West and Rocky Mountain Forests are
most important for biomass consumption and
regional air quality
Bailey (1994) classification
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Pacific Northwest/Cascade Forests. Annual Area
Burned
Regression against linear area burned
0.5
R252
0.25
Area burned / 106 Ha
1980
2000
1990
May-Oct mean Temperature
May-Oct mean Drought Code
1980
1990
2000
1990
1980
2000
Regressions explains 50-57 of variability in
annual area burned in forest ecosystems. Best
predictors are often Temperature or Fuel Moisture
Index.
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Trends in GISS western US mean July Met variables
Temperature / oC
Rainfall / mm day-1
GISS GCM predicts 1.8 K increase in western US
July mean temperature by 2055. How does this
impact wildfires?
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Observed
Annual area burned 1980-2055
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.
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Annual total W. US Forest Fire Biomass
Consumption 1996-2055
Observed
Predicted
Use stochastic placement of wildfires within
ecosystem and ecosystem specific fuel loads.
1996-2004 mean / Tg yr-1 Observed 19.15 Predicte
d 20.67
50
Predicted mean biomass consumption for 2045-2054
is 50 greater than during 1996-2004
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Predicted Organic Carbon concentrations in W. US
for 2046-2050
2046
2047
2048
2049
2050
Implications for visibility. Mean summertime visi
bility degrades from 13.2dv (1996-2004) to
13.8dv (2046-2050).
2046-2050 A1 scenario CO2 1996-2000
OC concentration / µg m-3
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Summertime OC in 2046-2050 predicted to increase
by 20-25.
1996
1997
1998
1999
2000
But need longer model runs.
Jun-Aug mean at IMPROVE sites
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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 a
nnual area burned in western US capture 50-57 of
interannual variablity. Temperature and fuel
moisture are best predictors. Using GISS GCM ou
tput, 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.