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EFFECTS OF CLIMATE CHANGE ON FOREST FIRES
OVER NORTH AMERICA AND IMPACT ON U.S. OZONE
AIR QUALITY
Rynda Hudman 1,2, Dominick Spracklen 1,3, Jennifer Logan3
Loretta J. Mickley3, Maria Val Martin3, Shiliang Wu3,4, Rose Yevich3,
Alan Cantin5, Mike Flannigan5, Tony Westerling6
Affiliations: 1 School of Engineering, Harvard
2 Now at UC Berkeley
3 Now at University of Leeds
4 Now at Michigan Tech
5 Canadian Forest Service
6 UC Merced
OBSERVED INCREASE IN WILDFIRE ACTIVITY OVER
NORTH AMERICA
Area burned in Canada has
increased since the 1960s,
correlated with temp. increase.
5 year means
[Gillett et al., 2004]
Increased fire frequency over
western U.S. in recent decades
– related to warmer temp.,
earlier snow melt.
[Westerling et al., 2007]
PREDICTING FUTURE FIRE IMPACTS ON U.S. OZONE
OBSERVED AREA BURNED
WEATHER & FUEL
MOISTURE/ FIRE SEVERITY
AREA BURNED
PREDICTION
Yearly Area Burned = C1X1 + C2X2 + … + C0
FUTURE AREA BURNED
GISS GCM
Output
(2050, A1B)
GEOS-CHEM CTM
Emissions
Future Fire Impacts on
U.S. ozone air quality
PREDICTED BIOMASS CONSUMPTION BY FIRES IN
THE WESTERN U.S., 1996-2055
Results shown as the number of standard deviations away
from the mean for 1996-2005
50% increase in biomass consumption by 2050  40%
increase in mean summertime aerosol concentration
[Further details see Spracklen et al., JGR, in review]
PROJECTED WESTERN U.S. WILDFIRE NOx EMISSIONS
Ozone production generally limited by supply of NOx
2046 – 2055 PROJECTED WILDFIRE
NOx EMISSIONS ARE 50% LARGER
THAN 1996-2005
* We assume forest emission factor of
1.6 g NO/kg DM
PREDICTED AFTERNOON (1-5pm) JULY MEAN OZONE
ENHANCEMENT 1-3 PPBV
4 Years Future (2050) vs. 4 Years Present (2000)
Ozone change due to future wildfire*
* Note: climate effects
have been subtracted
out
Consistent with these results, recent observational estimates of regional
enhancements of 2 ppbv for each 1 million acres burned [Jaffe et al., 2008]
REGRESSIONS CAPTURE VARIABILITY IN REGIONS WITH
LARGEST AREA BURNED
Historical Area Burned
Regressions ‘capture’ 15 – 62% of
variability over Canada and Alaska.
R2 of Area Burned regressions
[Nancy French, MTU]
[Stocks et al., 1999]
REGRESSION AGAINST AREA BURNED: Taiga Plains
AREA BURNED
ALASKA/CANADA SUMMARY
Most Common Predictors:
•Monthly/Seas. 500 mb GPH Anomaly
•Max/Mon./Seasonal Severity Rating
Large-scale Ocean/Atmosphere circulation related to fire activity [ e.g., Skinner et al.,
1999, 2002; Duffy et al., 2005] ; Severity Rating &Temp common predictor in previous
regression [Balschi et al., 2008]
DOES RAIN OFFSET TEMPERATURE INCREASE?
Simulated May – August 2046-2055 vs. 1996-2005
June 500mb anomaly over Fairbanks, Alaska (1940 – 2006)
GISS Mean 1999-2008 : -1.4 dm
2045-2054 : 0.5 dm
[Fairbanks GPH Courtesy of Sharon Alder, BLM]
AREA BURNED PROJECTIONS
34% increase over Alaska, 8% change over Canada w/ large regional variability
Difference from other studies likely due to future scenario or GCM 
need envelope study with multiple GCMs & scenarios.
PRESENT DAY FIRE IMPACTS ON OZONE
Ozone enhancement from NA biomass burning 0-2 km
Simulated July 2004 mean
Max enhancement during July 15-24 2004
CONCLUSIONS
•Regressions capture much of the variability in annual area burned over the
western U.S. (24-57%), Alaska (53-57%), and Canada (15-62%). Key
predictors : 500 mb GPH anomaly & severity rating.
• 2050 climate change (A1B) increases annual mean area burned: Alaska
(+34%) and the western U.S. (+54%) relative to the present-day, but unlike
previous studies little change over Canada as a whole (8%), due to increases
in GCM precipitation (scenario/GCM dependent).
• Future fires increase NOx emissions over the western United States by 50%,
resulting in a large scale 1-3 ppbv enhancement in summertime afternoon
ozone, though inter annual effects larger.
• Long-range transport impacts largest over central U.S. with large scale
episodic ozone enhancements > 5 ppbv over large areas of the Northern U.S.,
comparable to W. U.S. ozone enhancements.
EXTRAS
CANADIAN FUTURE AREA BURNED PROJECTIONS
Increased precipitation counterbalanced by increased 500mb GPH anom.
Taiga Plains
Increases of ~15% in summertime precipitation  -40% AB
Boreal Shield West
Increased GPH anomaly counterbalances increases in precipitation  + 21%
AB
Soja et. al.
We capture between 50-60% for the two Alaska ecoregions
R2 = 53.3%
R2 = 57.1%
Regression (in red) chosen from 22 surface met
& FWI variables (1959 – 2006) and 500 mb data
from Fairbanks, Alaska
Note: DSR = Daily Severity Rating = f(T, RH, Rain)
Ecozones
Both DSR and 500 mb anom govern variability in this region
R2 = 53.3%
Ecozones
Area Burned and GISS Regression
Met Corrected with:
1996-2006
1980-1989
60805.7 (500 mb anom) + 21113.9 (MaxDSR) - 61730.3
49665.6 (500 mb anom) + 63399.6(MeanTemp) – 838600
Station
location
Fire
distribution
11
4
51
12
9
14
52
61
53
62
Ecoregions
4- Taiga Plains (120m)
62- Boreal Shield East (170m)
14- Montane Cordillera (747m)
11- Taiga Cordillera(415m)
52 – Taiga Shield East (27m)
12- Boreal Cordillera (415m)
9- Boreal Plains (388m)
51- Taiga Shield West (192m)
61- Boreal Shield West (348m)
53 – Hudson Plains(152m)
….AND FUEL CONSUMPTION
Fuel bed map (1x1 km resolution) from Nadeau et al, [2005]
[Maria Val Martin]
NEW EMISSIONS WILL ACCOUNT FOR SEASONAL CHANGE IN
FUEL MOSITURE…
7.00
Fuel Consumption Changes in Black Spruce-Lichen
Drier Conditions
Woodland Forest
Late Season
Fuel Consumption (Kg/m2)
6.00
5.00
Total
Above Ground
Ground Layer
4.00
Wetter Conditions
3.00Early Season
2.00
1.00
0.00
90% 1070% 1060% 1050% 1040% 1030% 1020% 10hr&1000-hr, hr&1000-hr, hr&1000-hr, hr&1000-hr, hr&1000-hr, hr&1000-hr, hr&1000-hr,
120% Duff 110% Duff 100% Duff 90% Duff
70% Duff
50% Duff
30% Duff
Fuel Humidity Conditions
[Maria Val Martin]