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Wildfire in the western United States in the mid-21st century and consequences for air quality: Results from an ensemble of climate model projections.

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Presentation on theme: "Wildfire in the western United States in the mid-21st century and consequences for air quality: Results from an ensemble of climate model projections."— Presentation transcript:

1 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 Yue Jennifer A. Logan Jed Kaplan, Univ of Geneva NASA Air Quality Applied Sciences Team serves as a bridge between NASA science and environmental management.

2 Millions of people in US live in areas with unhealthy levels of ozone or particulate matter (PM 2.5 ). Number of people living in areas that exceed the national ambient air quality standards (NAAQS) in 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. Ozone daily maximum 8-hour average PM hour average or annual average

3 3 Life cycle of particulate matter (PM, aerosols) nucleation coagulation condensation wildfires combustion soil dust sea salt cycling ultra-fine (<0.01  m) fine (  m) cloud (1-100  m) combustion volcanoes agriculture biosphere coarse (1-10  m) scavenging precursor gases SO 2 -- sulfur dioxide NOx -- nitrogen oxides Soup of chemical reactions NOx VOCs Organic carbon SO 2 NH 3 SO 2 VOCs -- volatile organic compounds NH 3 -- ammonia Black carbon

4  Hayman fire, June 8-22, 2002  56,000 ha burned  30 miles from Denver and Colorado Springs Colorado Dept. of Public Health and Environment Vedal et al., 2006 June 8, 2002 June 9, 2002 PM 10 = 372 μg/m 3 PM 2.5 = 200 μg/m 3 Standard = 35 µg/m 3 PM 10 = 40 μg/m 3 PM 2.5 = 10 μg/m 3 Unhealthy air quality in Denver Effects of wildfires on air quality in cities in Western US can be very dramatic.

5 Fire activity had a big impact on California air quality in Unhealthy air Very unhealthy air Rim Fire Aug 28 Aug 30 Timeseries of 3-hour average PM 2.5 concentrations in Foothills Area August 20 August 31 PM2.5 (  g m -3 ) Hazardous levels > 250  g m -3 Will fire change in the future climate? Very unhealthy

6 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 yr means area burned obs temperature

7 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.

8 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 AnnualDJF JJA

9 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 meteorology Future area burned Start with the past. 2 approaches

10 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 DSW CCS 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)

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

12 Area burned = f 1 (Temp) x f 2 (RH) x f 3 (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.

13 Parameterization works for forested regions, but not for regions where meteorology from previous seasons matter. ObsFit Yue et al., 2013

14 Relationship between observed meteorology + area burned + Future meteorology Future area burned Start with the past.

15 Use of an ensemble of 15 climate models improves confidence in the results. Changes in 2050s climate in the West. Temperature increases 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

16 Wildfire area burned increases across the western United States by the 2050s timeframe. Relationship between observed meteorology + area burned + Future meteorology Future area burned Results from regressions approach. Shown are median results. Yue et al., 2013

17 Models predict increases in area burned of % across the West, depending on ecoregion. The models match the mean area burned fairly well in present-day spread of models Obs Median of models Area burned (ha) +40% +60% +70% +60% +20% 100% Results are from regressions. Yue et al., 2013

18 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 Coastal Shrub Ratio of area burned Ratio of future to present-day area burned Pacific Northwest Desert Southwest Nevada Mountains Rocky Mountains Eastern Rockies median Forest Median changes: 40-70% increase in forested regions 60% increase in grasslands Doubling in Southwest

19 Parameterization method shows similar increases in area burned, and also provides seasonality. Predicted area burned shows large increases in 2050s during peak months. future present-day X4 increase X2 increase Yue et al., 2013 Units = 10 4 hectares

20 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

21 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.

22 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

23 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.  Organic Carbon, OC  Black Carbon, BC

24 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.

25 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

26 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.

27 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 % in Southwest California. 2 methods

28 Main findings. Area burned by wildfires increases % 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

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30 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. fires area

31 New parameterization predicts yearly variability and seasonality in south west California Area burned in Southern California increases % by 2050s relative to present-day. Yue et al., 2013 R 2 =0.64 Southwest CA Seasonality Two approaches used in each ecoregion. Area burned in ~2050 / Present-day R P R South west California Central California Sierra Nevada


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