Climate Change Indicators in the United States: Wildfires
www.epa.gov/climate-indicators - Updated August 2016
Wildfires
This indicator tracks the frequency, extent, and severity of wildfires in the United States.
Background
Together, forests, shrubland, and grassland cover more than half of the land area in the United States.1
These ecosystems are important resources, both environmentally and economically. Although wildfires
occur naturally and play a long-term role in the health of these ecosystems, climate change threatens to
increase the frequency, extent, and severity of fires through increased temperatures and drought (see
the U.S. and Global Temperature and Drought indicators). Earlier spring melting and reduced snowpack
(see the Snowpack indicator) result in decreased water availability during hot summer conditions, which
in turn contributes to an increased wildfire risk, allowing fires to start more easily and burn hotter. An
increase in the length of the fire season has been observed in some areas.2 In addition to climate
change, other factors—like the spread of insects, land use, fuel availability, and management practices,
including fire suppression—play an important role in wildfire frequency and intensity. All of these
factors influencing wildfires vary greatly by region and over time, as do variations in precipitation, wind,
temperature, vegetation types, and landscape conditions. Therefore, understanding changes in fire
characteristics requires long-term records, a regional perspective, and consideration of many factors.3
Wildfires have the potential to harm property, livelihoods, and human health, particularly as population
centers expand into wild land areas. The recreation and timber industries depend on healthy forests,
and wildfire smoke has been directly linked to poor air quality and illness, even in communities far
downwind.4,5 Fire-related threats are increasing, especially as more people live in and around forests,
grasslands, and other natural areas.6 The United States spends more than $1 billion every year to fight
wildfires and spent more than $2 billion in 2015.7 These efforts have resulted in the deaths of hundreds
of firefighters since 1910.8
Beyond the human impact, wildfires also affect the Earth's climate. Forests in particular store large
amounts of carbon. When they burn, they release carbon dioxide into the atmosphere, which in turn
contributes to climate change.
About the Indicator
This indicator defines wildfires as "unplanned, unwanted wildland fire[s]" in forests, shrubland, and
grassland, where "the objective is to put the fire out."9 This indicator tracks three aspects of wildfires
over time: the total number of fires (frequency), the total land area burned (extent), and the degree of
damage that fires cause to the landscape (severity). The total area and total number of fires are tracked
by the National Interagency Fire Center, which compiles reports from local, state, and federal agencies
that are involved in fighting wildfires. The U.S. Forest Service tracked similar data using a different
reporting system until 1997. Those data have been added to this indicator for comparison. Wildfire
severity is measured by comparing the "greenness" of satellite images taken before and after a fire to
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Climate Change Indicators in the United States: Wildfires
www.epa.gov/climate-indicators - Updated August 2016
classify how severely the land has been burned. Burn severity provides an indication of the ecological
damage and how long the effects of wildfires are likely to last.
Although some nationwide fire data have been collected since the early 1900s, this indicator starts in
1983 (Figures 1 and 2) and 1984 (Figures 3, 4, and 5), when nationwide data collection became more
complete and standardized.
Key Points
• Since 1983, the National Interagency Fire Center has documented an average of 72,000 wildfires
per year (see Figure 1). Compiled data from the Forest Service suggest that the actual total may
be even higher for the first few years of nationwide data collection that can be compared. The
data do not show an obvious trend during this time.
• The extent of area burned by wildfires each year appears to have increased since the 1980s.
According to National Interagency Fire Center data, of the 10 years with the largest acreage
burned, nine have occurred since 2000, including the peak year in 2015 (see Figure 2). This
period coincides with many of the warmest years on record nationwide (see the U.S. and Global
Temperature indicator).
• The late 1990s were a period of transition in certain climate cycles that tend to shift every few
decades.10 This shift—combined with other ongoing changes in temperature, drought, and
snowmelt—may have contributed to warmer, drier conditions that have fueled wildfires in parts
of the western United States.1112
• Of the total area burned each year from 1984 to 2014, the proportion of burned land suffering
severe damage has ranged from 5 to 21 percent (see Figure 3).
• Land area burned by wildfires varies by state. Fires burn more land in the western United States
than in the East, and parts of the West and Southwest show the largest increase in burned
acreage between the first half of the record (1984-1999) and the second half (2000-2014) (see
Figures 4 and 5).
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Climate Change Indicators in the United States: Wildfires
www.epa.gov/climate-indicators - Updated August 2016
Figure 1. Wildfire Frequency in the United States, 1983-2015
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Climate Change Indicators in the United States: Wildfires
nrr\ www.epa.gov/climate-indicators - Updated August 2016
Figure 2. Wildfire Extent in the United States, 1983-2015
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Climate Change Indicators in the United States: Wildfires
www.epa.gov/climate-indicators - Updated August 2016
Figure 3. Damage Caused by Wildfires in the United States, 1984-2014
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This figure shows the distribution of acreage burned by large wildfires, based on the level of damage
caused to the landscape—a measure of wildfire severity. Large wildfires are defined as fires with an area
larger than 1,000 acres in the western United States and 500 acres in the eastern United States. The total
acreage shown in Figure 3 is slightly less than the total in Figure 2 because Figure 3 is limited to large
fires and because a few areas did not have sufficient satellite imagery to allow damage to be assessed.
Data source: MTBS, 20161'
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Unburned to low
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Climate Change Indicators in the United States: Wildfires
www.epa.gov/climate-indicators - Updated August 2016
Figure 4. Average Annual Burned Acreage by State, 1984-2014
0 1 2 3 4 5 6
Slates colored light gray did not have any fires that were large enough to be included in this analysis.
This map shows the average number of acres burned in each state per year as a proportion of that
state's total land area. Darker-shaded states have the largest proportion of acreage burned. For
reference, there are 640 acres in a square mile; therefore, an average burned area of 6.4 acres per
square mile would mean that fires burned 1 percent of a state's total land area. A few states did not
have any fires that were large enough to be included in this analysis. Visit this indicator online at
www.epa.gov/climate-indicators for an interactive version of this map.
Data source: MTBS, 201618
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Climate Change Indicators in the United States: Wildfires
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Figure 5. Change in Annual Burned Acreage by State Between 1984-1999 and 2000-2014
-A -3 -2 -1 -0.2 0.2 1 2 3 4
States colored light gray did not have any fires tin at were large enough to be included in this analysis.
This map shows how the number of acres burned in each state as a proportion of that state's total land
area has changed over time, based on a simple comparison between the first half of the available years
(1984-1999) and the second half (2000-2014). For reference, there are 640 acres in a square mile;
therefore, a change of 6.4 acres per square mile would mean that burned area increased by 1 percent of
a state's total land area. A few states did not have any fires that were large enough to be included in this
analysis. Visit this indicator online at www.epa.gov/climate-indicators for an interactive version of this
map.
Data source: MTBS, 201619
Indicator Notes
Many environmental impacts associated with climate change can affect wildfire frequency, extent, or
severity, including changes in temperature, precipitation, and drought. Human activities and land
management practices also affect wildfire activity, and preferred practices in wildfire management have
evolved over time, from older policies that favored complete wildfire prevention to more recent policies
of wildfire suppression and controlled burns. While this indicator is limited to "wildland" fires, it includes
fires that encroach on—or perhaps started in—developed areas. Increased development in previously
wild lands could also influence trends in wildfire frequency and extent. The total number of fires may
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Climate Change Indicators in the United States: Wildfires
www.epa.gov/climate-indicators - Updated August 2016
also vary due to reporting irregularities, as fires that split or merge together across jurisdictional lines
may be counted differently.
Along with the influence of ongoing climate change, wildfire patterns can be influenced by natural
climate cycles that tend to shift every few decades. Thus, the approximately 30 years of data shown
here may not be enough to draw conclusions about long-term trends. While a longer record would be
ideal, data from before 1983 are not consistent enough nationally to be included in this indicator.
Data Sources
The full set of wildfire frequency and burned acreage data in Figures 1 and 2 comes from the National
Interagency Fire Center, which compiles wildfire reports sent from local, state, and federal entities that
are involved in fighting fires. These data are available online at:
www.nifc.gov/firelnfo/firelnfo statistics.html. Additional data were provided by the U.S. Forest Service
based on a different set of records, referred to as Smokey Bear Reports. Burn severity data and state-by-
state acreage totals in Figures 3, 4, and 5 come from a multi-agency project called Monitoring Trends in
Burn Severity, which maintains a database of wildfire events across the United States. These data are
publicly available at: www.mtbs.gov/data/search.html.
1 MRLC (Multi-Resolution Land Characteristics) Consortium. 2015. National Land Cover Database 2011 (NLCD
2011) product statistics, www.mrlc.gov/nlcdll stat.php.
2 Westerling, A.L. 2016. Increasing western U.S. forest wildfire activity: Sensitivity to changes in the timing of
spring. Phil. Trans. R. Soc. B. 371:20150178.
3 Stein, S.M., J. Menakis, M.A. Carr, S.J. Comas, S.I. Stewart, H. Cleveland, L. Bramwell, and V.C. Radeloff. 2013.
Wildfire, wildlands, and people: Understanding and preparing for wildfire in the wildland-urban interface. Gen.
Tech. Rep. RMRS-GTR-299. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain
Research Station, www.fs.fed.us/openspace/fote/wildfire-report.html.
4 Johnston, F.H., S.B. Henderson, Y. Chen, J.T. Randerson, M. Marlier, R.S. DeFries, P. Kinney, D. Bowman, and M.
Brauer. 2012. Estimated global mortality attributable to smoke from landscape fires. Environ. Health Persp.
120(5):695-701. www.ncbi.nlm.nih.gov/pmc/articles/PMC3346787.
5 Fann, N., T. Brennan, P. Dolwick, J.L Gamble, V. Ilacqua, L. Kolb, C.G. Nolte, T.L. Spero, and L. Ziska. 2016.
Chapter 3: Air quality impacts. The impacts of climate change on human health in the United States: A scientific
assessment. U.S. Global Change Research Program, https://health2016.globalchange.gov.
6 National Association of State Foresters. 2009. Quadrennial fire review, www.nifc.gov/policies/pol ref QFR.html.
7 NIFC (National Interagency Fire Center). 2016. Historical wildland fire information: Federal firefighting costs:
Suppression only (1985-2015). www.nifc.gov/firelnfo/firelnfo documents/SuppCosts.pdf.
8 NIFC (National Interagency Fire Center). 2015. Wildland fire fatalities by year (1910-2014).
www.nifc.gov/safetv/safetv documents/Fatalities-bv-Year.pdf.
9 NWCG (National Wildfire Coordinating Group). 2015. Glossary of wildland fire terminology. Updated October
2015. www.nwcg.gov/glossarv-of-wildland-fire-terminology.
10 For example, see: Peterson, W.T., and F.B. Schwing. 2003. A new climate regime in northeast Pacific ecosystems.
Geophys. Res. Lett. 30(17).
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Climate Change Indicators in the United States: Wildfires
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11 Kitzberger, T., P.M. Brown, E.K. Heyerdahl, T.W. Swetnam, and T.T. Veblen. 2007. Contingent Pacific-Atlantic
Ocean influence on multicentury wildfire synchrony over western North America. P. Natl. Acad. Sci. USA
104(2) :543-548.
12 Westerling, A.L. 2016. Increasing western U.S. forest wildfire activity: Sensitivity to changes in the timing of
spring. Phil. Trans. R. Soc. B. 371:20150178.
13 NIFC (National Interagency Fire Center). 2016. Total wildland fires and acres (1960-2015). Accessed March
2016. www.nifc.gov/firelnfo/firelnfo stats totalFires.html.
14 USDA (U.S. Department of Agriculture) Forest Service. 2014. 1991-1997 wildland fire statistics. Prepared by
USDA Forest Service, State and Private Forestry, Fire and Aviation Management staff, and supplemented with
historical records provided by Forest Service staff, April 2014.
15 NIFC (National Interagency Fire Center). 2016. Total wildland fires and acres (1960-2015). Accessed March
2016. www.nifc.gov/firelnfo/firelnfo stats totalFires.html.
16 Short, K.C. 2015. Sources and implications of bias and uncertainty in a century of U.S. wildfire activity data. Int. J.
Wildland Fire 24(7):883-891.
17 MTBS (Monitoring Trends in Burn Severity). 2016. MTBS data summaries, www.mtbs.gov/data/search.html.
18 MTBS (Monitoring Trends in Burn Severity). 2016. MTBS data summaries, www.mtbs.gov/data/search.html.
19 MTBS (Monitoring Trends in Burn Severity). 2016. MTBS data summaries, www.mtbs.gov/data/search.html.
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