Wildfire in the western United States in the mid-21st century and consequences for air quality:

Results from an ensemble of climate model projections.

Loretta J. Mickley Xu YueJennifer A. Logan

Jed Kaplan, Univ of Geneva

NASA Air Quality Applied Sciences Team serves as a bridge between NASA science and environmental management.

Millions of people in US live in areas with unhealthy levels of ozone or particulate matter (PM2.5).

Number of people living in areas that exceed the national ambient air quality standards (NAAQS) in 2010.

Bars on barplot will change with changing emissions.

Climate change could also change the size of these bars, by changing the day-to-day weather.

Ozonedaily maximum 8-hour average

PM2.5

24-hour average or annual average

3

Life cycle of particulate matter (PM, aerosols)

nucleation coagulation

condensation

wildfirescombustion

soil dustsea salt

. . ... .

cycling

ultra-fine(<0.01 mm)

fine(0.01-1 mm)

cloud(1-100 mm)

combustionvolcanoes

agriculturebiosphere

coarse(1-10 mm) scavenging

precursor gases

SO2 -- sulfur dioxideNOx -- nitrogen oxides

Soup of chemical reactions

NOxNOx

NOx

NOxNOx

VOCs

VOCsVOCs

VOCs

Organic carbon

SO2

NH3

SO2

VOCs -- volatile organic compoundsNH3 -- ammonia

Black carbon

Hayman fire, June 8-22, 2002 56,000 ha burned 30 miles from Denver and Colorado Springs

Colorado Dept. of Public Health and EnvironmentVedal et al., 2006

June 8, 2002 June 9, 2002 PM10 = 372 μg/m3

PM2.5 = 200 μg/m3

Standard = 35 µg/m3

PM10 = 40 μg/m3

PM2.5 = 10 μg/m3

Unhealthy air quality in Denver

Effects of wildfires on air quality in cities in Western US can be very dramatic.

Fire activity had a big impact on California air quality in 2013.

Unhealthy air

Very unhealthy air

Rim Fire

Aug 28

Aug 30

Timeseries of 3-hour average PM2.5 concentrations in Foothills Area

August 20 August 31

PM2.

5 (m

g m

-3)

Hazardous levels > 250 mg m-3

Will fire change in the future climate?

Very unhealthy

Gillett et al., 2004

Area burned in Canada has increased since the 1960s, correlated with temperature increase.

Westerling et al., 2007

Increased fire frequency over the western U.S. since 1970, related to warmer temperatures and earlier snow melt.

Observations suggest that fires are increasing in North America.

1970 2000

5 yr means

area burned

obs temperature

1960 2000

IPCC AR4 models show increasing temperatures across North America by 2100 in A1B scenario.

IPCC, 2007

Change in surface temperatures in 2100, relative to present-day.

Results for precipitation changes are not so clear.

Future regional predictions for precipitation show large variation across North America.

Percent change in 2100 precipitation relative to present-day

Number of models showing increasing precipitation

IPCC 2007

most models

few models

Annual DJF JJA

How do we predict fires in a future climate?We don’t have a good mechanistic approach for modeling wildfires.

JJA Temperature increase by 2100

Use ensemble of climate models to gain confidence in prediction.

Relationship between observed meteorology + area burned + Future

meteorologyFuture area burned

Start with the past.

2 approaches

Approach 1. Regression method. Regress meteorological variables and fire indexes onto annual mean area burned in each of six ecoregions with a stepwise approach.

PNW

ERM

NMS

RMF

DSWCCS

Ecoregions are aggregates of those in Bailey et al. (1994)

Identify the meteorological variables and fire indexes that best predict area burned.

Include lagged met variables.

Best predictors: Temp, RH, precip, Build-up Index, Drought code, Duff moisture code. E.g., Area burned in Nevada/ semi-desert = f ( + T summer max that year

+ RH and rainfall previous years)

Predicted fires match observed area burned reasonably well. Least best fit is in Southern California.

Obs Fit

Area burned in many ecoregions depends on previous year’s relative humidity, rainfall, or temp. Yue et al., 2013

CCS

PNW

NMS

DSW

RMF ERM

Area burned = f1(Temp) x f2(RH) x f3(rainfall)

Fire potential coefficients are (α) chosen to match long-term area burned for each ecoregion.

Scheme can predict seasonality of fires on the 1°x1° grid.

Approach 2. Parameterization method. Parameterize daily area burned in each grid square as a function of that day’s temperature, relative humidity, and rainfall.

Parameterization works for forested regions, but not for regions where meteorology from previous seasons matter.

Obs Fit

Yue et al., 2013

Relationship between observed meteorology + area burned + Future

meteorologyFuture area burned

Start with the past.

Use of an ensemble of 15 climate models improves confidence in the results.

Changes in 2050s climate in the West.• Temperature increases 2-2.5 K.• Changes in precip and relative humidity

are small and not always robust.

Next step: apply meteorology from climate models to the two fire prediction schemes.

Yue et al., 2013

Wildfire area burned increases across the western United States by the 2050s timeframe.

Relationship between observed meteorology + area burned + Future

meteorologyFuture area burned

Results from regressions approach.Shown are median results.

Yue et al., 2013

Models predict increases in area burned of 20-100% across the West, depending on ecoregion.

The models match the mean area burned fairly well in present-day.

1986-2000 2051-2065

spread of models

Obs

Median of models

1986 2065

Area

bur

ned

(ha)

+40%

+60%

+70%

+60%

+20%

100%

Results are from regressions.

Yue et al., 2013

Median model results show an increase in area burned in all regions, but some scatter.

Yue et al., 2013

CCS

PNW

NMS

DSW

RMF ERM

California Coast

al Shrub

Rat

io o

f are

a bu

rned

Ratio of future to present-day area burned

Pacific N

orthwest

Desert Southwest

Nevada M

ountains

Rocky M

ountains

Easte

rn Rockies

median

Fore

st

Fore

st

Median changes:

40-70% increase in forested regions

60% increase in grasslands

Doubling in Southwest

Parameterization method shows similar increases in area burned, and also provides seasonality.

Predicted area burned shows large increases in 2050s during peak months.

futurepresent-day

X4 increase X2 increase

Yue et al., 2013

Units = 104 hectares

Parameterization method also reveals a lengthening of wildfire season.

Fire season is defined as those days when daily area burned is larger than 100 ha in at least one grid box.

observations

present-day future

Predicted number of days of fire season across the Western US.

Mean increase is ~3 weeks.

Yue et al., 2013

What about trends in vegetation in the future climate and the issue of reburning?

Results from LPJ dynamic vegetation model show relatively little change in vegetation in 2050s atmosphere.

We placed fires randomly within each sub-ecoregion to minimize reburning of gridsquares.

GEOS-CHEM Global chemistry model

Ensemble of climate models

Median area burned

Emissions = area burned x fuel consumption x emission factors

How will changing area burned affect air quality?

Future air quality

Future meteorology

Yue et al., 2013

Organic particles increase in future atmosphere over the western U.S. in summer, especially during extreme events.

Change in summertime mean PM2.5 in ~2050s, relative to present-day.

D Organic Carbon, OC D Black Carbon, BC

Organic particles increase in future atmosphere over the western U.S. in summer, especially during extreme events.

Yue et al., 2013

Cumulative probability of daily mean concentrations of organic particles

2050s

Present-day

doubling

Distribution of daily OC concentrations, May-Oct in Rocky Mountains.

Visibility decreases during extreme events from 130 km to 100 km.

These changes are underestimates due to model resolution.

What do these increases in wildfire aerosol mean for human health?

Ongoing project with Yale will look at health impacts of these increases.

Yue et al., 2013

% area burned

% OC particles

How do we improve fire predictions in S. California?

Fire plumes (Oct. 2007) Composite Santa Ana winds

The largest fires in California are associated with Santa Ana events.

Hughes and Hall (2010)

Need finely resolved wind fields to capture Santa Ana in meteorological record.

1980-2009 fire occurence

Yue et al., in review

• Divide up California into smaller ecosystems

• Use finer grid• Parameterize effects of elevation,

population, and Santa Anas.

Improving predictions of area burned in Southern California.

Area burned

Surface pressure anomalies

Santa Ana winds are associated with surface pressure anomalies that can be captured by climate models.

R P

Ratio of future area burned to present-day.

Area burned increases by 50-100% in Southwest California.

2 methods

Main findings.• Area burned by wildfires increases 20-170% across the West by the

2050s, depending on the ecosystem.

• During peak months, area burned nearly doubles in Eastern Rockies/Great Plains and quadruples in the forested Rockies.

• Wildfire season may increase by ~3 weeks in the West in future.

• Increased smoke from wildfires may thwart efforts to regulate air quality in coming decades. This is a climate penalty.

Wildfires in Quebec the same day.Haze over Boston on May 31, 2010

Seasonality of fires in Southern California

South-West Cal.

Central Western Cal.

Sierra Nevada

Fire regions

Largest area burned in SW California.

October peak associated with the Santa Ana winds, which are underestimated by large scale models as they lack the detailed topography: need large-scale approach

num. firesarea

New parameterization predicts yearly variability and seasonality in south west California

Area burned in Southern California increases 20-100% by 2050s relative to present-day.

Yue et al., 2013

R2=0.64

Southwest CA

Seasonality

Two approaches used in each ecoregion.

Area burned in ~2050 / Present-day

R P R PR South west California

Central California

Sierra Nevada