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 ParkShiliang Wu, Rose Yevich

Mike Flannigan, Tony Westerling, Dan Jaffe

Boreal wildfire and climate

OC / BC aerosols

GHGsCO

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 CO2 compared to pre-industrial CO2

Historical Wildfire Records in Western US

Westerling et al. 2006

Fre

quen

cyof

larg

e fir

es Large increase in wildfires after the mid 1980s.

Biogenic OCWildfire OC

Emissions of OC

Large interannual variability in wildfire emissions. How does this impact atmospheric OC?

Large Fire Years

Observations (IMPROVE)

GEOS-chemGlobal CTM

OC

con

cent

ratio

n /

μg

m-3

1.5

2.0

1980-1984

OCbiob emission / TgO

C c

once

ntra

tion

/ μ

g m

-3

IMPROVEGEOS-chem

1.0

0.1 0.2 0.3

Jun-Aug mean at IMPROVE sites W of 100oW

Impact of variability of fires on atmospheric OC

Interannual variability in summertime OC concentrations driven by wildfires.

GEOS-chemClimatological 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

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

Daily forest moisture parameters

Area burned database (1o x 1o)

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)

6.7105.8

17.525.4

3.611.6

12.8151.6

4.851.8

4.59.8

1980 – 2004 Totals [Westerling et al., 2002]Area Burned / 106 acresBiomass 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.

R2=52%

Are

a b

urn

ed /

106

Ha 0.5

0.25

1980 20001990

1980 1990 2000 200019901980

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?

Te

mp

era

ture

/ oC

Ra

infa

ll / m

m d

ay-1

Observed

PredictedAnnual 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

Annual total W. US Forest Fire Biomass Consumption 1996-2055

ObservedPredicted

Predicted mean biomass consumption for 2045-2054 is 50% greater than during 1996-2004

1996-2004 mean / Tg yr-1

Observed 19.15Predicted 20.67

Use stochastic placement of wildfires within ecosystem and ecosystem specific fuel loads.

+50%

Predicted Organic Carbon concentrations in W. US for 2046-2050

1996 1997 1998 1999 2000

2046 2047 2048 2049 2050

2046-2050 A1 scenario CO2

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

con

cent

ratio

n /

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 2045-2055 (over 1995-2004) resulting in mean summertime OC to increase by 20-25%.