Wildfires
Identification
1.	Indicator Description
This indicator tracks wildfire frequency, total burned acreage, and burn severity in the United States
from 1983 to 2015. Although wildfires occur naturally and play a long-term role in the health of
ecosystems, climate change threatens to increase the frequency, extent, and severity of fires through
increased temperatures and drought. Earlier spring melting and reduced snowpack result in decreased
water availability during hot summer conditions, which in turn contributes to an increased risk of
wildfires, allowing fires to start more easily and burn hotter. Thus, while climate change is not the only
factor that influences patterns in wildfire, the many connections between wildfire and climate make this
indicator a useful tool for examining a possible impact of climate change on ecosystems and human
well-being. Wildfires are also relevant to climate because they release carbon dioxide into the
atmosphere, which in turn contributes to additional climate change.
Components of this indicator include:
•	Wildfire frequency (Figure 1).
•	Burned acreage from wildfires (Figure 2).
•	Wildfire burn severity (Figure 3).
•	Burned acreage from wildfires by state over time (Figures 4 and 5).
2.	Revision History
May 2014: Indicator published.
June 2015: Updated Figures 1 and 2 on EPA's website with data through 2014. Updated Figures 3
and 4 on EPA's website with data through 2013. Split Figure 4 into Figures 4 and 5.
April 2016: Updated Figures 1 and 2 on EPA's website with data through 2015.
August 2016: Updated Figures 3, 4, and 5 with data through 2014.
Data Sources
3. Data Sources
Wildfire data come from three sources:
1.	Summary data for wildfire frequency and burned acreage from 1983 through 2015 (Figures 1
and 2) are provided by the National Interagency Coordination Center (NICC), housed within the
National Interagency Fire Center (NIFC).
2.	For comparison in Figures 1 and 2, EPA obtained a data set called the United States Department
of Agriculture (USDA) Forest Service Wildfire Statistics, which provides annual frequency and
burned acreage totals through 1997 based on a different counting approach.
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3. Burn severity (Figure 3) and state-by-state burn acreage (Figures 4 and 5) data were obtained
from the Monitoring Trends in Burn Severity (MTBS) project, sponsored by the Wildland Fire
Leadership Council (WFLC). The MTBS is a joint project of the USDA Forest Service Remote
Sensing Applications Center (RSAC) and the United States Geological Survey (USGS) Earth
Resources Observation and Science (EROS) Center. Other collaborators include the National Park
Service, other USGS and USDA research facilities, and various academic institutions. The project
provides data on individual wildfire incidents that meet certain size criteria (> 1,000 acres in the
western United States or > 500 acres in the eastern United States). These data were available
from 1984 to 2014.
The analysis in Figures 4 and 5 normalizes wildfire extent by the land area of each state. Land areas
come from the U.S. Census Bureau.
4. Data Availability
NIFC data for annual trends in wildfire frequency and acreage are available from the NIFC website at:
www.nifc.gov/firelnfo/firelnfo statistics.html. These NIFC data are also mirrored in the annual Wildland
Fire Summary and Statistics reports from 2000 through 2015 at:
www.predictiveservices.nifc.gov/intelligence/intelligence.htm. NIFC totals are based on raw fire
incidence data reported via the Incident Command System (ICS) Incident Status Summary Reports (ICS-
209 forms). Some raw ICS-209 forms are available for individual viewing at: https://fam.nwcg.gov/fam-
web/hist 209/report list 209.
The USDA Forest Service Wildfire Statistics represent a complementary approach to compiling fire
occurrence and extent data. These statistics come from annual Forest Service reports officially known as
annual "Wildland Fire Statistics," but more commonly called "Smokey Bear Reports." These compilation
reports are based on reports submitted to the Forest Service by individual state and federal agencies,
covering land within each agency's jurisdiction. Smokey Bear Reports were provided to EPA by Forest
Service researcher Karen Short. The Smokey Bear Report extent totals that appear in Figure 2 have also
been published in Short (2015).
MTBS project analyses use raw ICS-209 form data from 1984 to 2014 as the basis for further processing.
Summary data are publicly available at: http://mtbs.gov/dataaccess.html. This online database search
tool also provides more detailed and comprehensive records, including burned area classification for
each individual fire incident. Detailed records for this indicator were provided by MTBS staff.
The U.S. Census Bureau has published official land areas for each state in the Statistical Abstract of the
United States, available online at:
www2.census.gov/library/publications/2011/compendia/statab/131ed/2012-statab.pdf.
Methodology
5. Data Collection
This indicator presents three measures of wildfires over time reported on an annual basis: (1) the total
number of wildfires, (2) acreage burned by wildfires, and (3) the burn severity of those fires. For the
purposes of this indicator, wildfires encompass "unplanned, unwanted wildland fire[s] including
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unauthorized human-caused fires, escaped wildland fire use events, escaped prescribed fire projects,
and all other wildland fires where the objective is to put the fire out" (NWCG, 2015). A wildland is
defined as "an area in which development is essentially non-existent, except for roads, railroads,
powerlines, and similar transportation facilities." Fire severity is defined as the "degree to which a site
has been altered or disrupted by fire; loosely a product of fire intensity and residence time." These data
cover all fifty states.
Figures 1 and 2. Wildfire Frequency and Acreage in the United States, 1983-2015
Wildfire frequency and burn acreage data are based upon local-, state-, and national-level reporting of
wildland fire incidents submitted to the NIFC via the ICS-209 form (Fire and Aviation Management and
Predictive Services, 2009). The data captured in these forms can also be submitted to the NIFC using the
Incident Management Situation (SIT)-209 reporting application. The ICS-209 guidelines require that large
fires (100+ acres in timber and 300+ acres in grasslands) must be reported, but they do not set a
minimum fire size for reporting. Thus, the data set includes small fires, including some that may have
burned just a few acres or less.
Supplementary data come from annual Smokey Bear Reports, which are based on annual reports
submitted to the Forest Service by individual state and federal agencies. These original reports describe
fires taking place on land within each reporting agency's fire protection jurisdiction. The IJSDA Forest
Service stopped compiling Smokey Bear Reports after 1997.
Figure 3. Damage Caused by Wildfires in the United States, 1984-2014
MTBS uses satellite imagery to map burn severity and perimeters of large fires (> 1,000 acres in the
western United States or > 500 acres in the eastern United States). These thresholds are applied based
on the "West" and "East" regions shown in Figure TD-1.
Figure TD-1. Region Boundaries for MTBS Size Threshold Application

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MTBS starts primarily from ICS-209 reports and solicits additional data from the states if inclusion in ICS-
209 is unclear. Other sources for fire occurrence data include federal data, the National Fire Plan
Operations and Reporting System (NFPORS), and InciWeb. These records are compiled into a
standardized project database. MTBS identifies corresponding imagery using the Global Visualization
Image Selection (GLOVIS) browser developed by the USGS EROS Center. ArcGIS shape files and scene-
specific Advanced Very High Resolution Radiometer (AVHRR) greenness plots are incorporated into the
viewer to aid scene selection and determination of peak periods of photosynthetic activity. Pre-fire and
post-fire images are selected for each incident. Wildfires are analyzed on the scale of individual
incidents, but the data can also be aggregated at other spatial scales for analytical purposes.
Figures 4 and 5. Average Annual Burned Acreage and Change in Burned Acreage by State, 1984-2014
Figures 4 and 5 are based on acreage data for large fires as compiled by the MTBS program through the
analytical steps described above for Figure 3. These numbers are based on ICS-209 reports and
additional state data compiled by MTBS.
6. Indicator Derivation
Figures 1 and 2. Wildfire Frequency and Acreage in the United States, 1983-2015
NIFC compiles local, state, and national reports to create the annual summary statistics published
online. Data are aggregated to provide national, state and local statistics. EPA aggregated state-by-state
totals in the annual Smokey Bear Reports to generate additional measures of annual wildfire frequency
and extent.
Figure 3. Damage Caused by Wildfires in the United States, 1984-2014
Burn severity is a qualitative measure describing the degree to which a site has been altered by fire
(NWCG, 2015). MTBS uses the Normalized Burn Ratio (NBR) to measure burn severity. NBR is a
normalized index that uses satellite imagery from Landsat 5 and/or Landsat 7 TM/ETM bands 4 (near-
infrared) and 7 (mid-infrared) to compare photosynthetically healthy and burned vegetation. Pre- and
post-fire NBR are calculated to compare vegetation conditions before and after each wildfire.
The difference between pre- and post-fire NBRs is the Differenced Normalized Burn Ratio (dNBR).
Calculated dNBR values are compared to established severity classes to give a qualitative assessment of
the effects of fire damage. These classifications plus a full discussion of NBR and dNBR calculation
methodology are described at: http://burnseverity.cr.usgs.gov/pdfs/LAv4 BR CheatSheet.pdf.
Selected satellite images are also filtered through a complex sequence of data pre-processing, perimeter
delineation, and other data quality assurance techniques. These procedures are documented in full on
the MTBS website at: www.mtbs.gov/methods.html and in a 2005 report on western U.S. fires (MTBS,
2005).
The timing of the satellite imagery selected for analysis depends on the type of assessment that is
conducted for a given fire. The optimal assessment type is selected based on the biophysical setting in
which each fire occurs. MTBS conducts two main types of assessments:
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•	Initial Assessments compare imagery from shortly before and shortly after the fire, typically
relying on the first available satellite data after the fire—on the scale of a few days. These
assessments focus on the maximum post-fire data signal and are used primarily in ecosystems
that exhibit rapid post-fire vegetation response (i.e., herbaceous and particular shrubland
systems).
•	Extended Assessments compare "peak green" conditions in the subsequent growing season with
"peak green" conditions in the previous growing season, prior to the fire. These assessments are
designed to capture delayed first-order effects (e.g., latent tree mortality) and dominant
second-order effects that are ecologically significant (e.g., initial site response and early
secondary effects).
MTBS occasionally conducts a Single Scene Assessment, which uses only a post-fire image (either
"initial" or "extended"), when limited by factors such as data availability.
See: www.mtbs.gov/glossarv.html for a glossary of MTBS assessment terms.
Figure 3 was created by filtering MTBS's database output to remove any fires not meeting MTBS's size
criteria—although most such fires would not have been processed by MTBS anyway—and removing
fires classified as "prescribed," "wildland fire use," or "unknown." The resulting analysis is therefore
limited to fires classified as true "wildfires."
The total acreage shown in Figure 3 (the sum of the stacked burn severity sections) does not match the
total acreage in Figure 2 because the burn severity analysis in Figure 3 is limited to fires above a specific
size threshold (> 1,000 acres in the western United States and > 500 acres in the eastern United States)
and because the graph does not include acreage classified as "outside perimeter" or "non-processing
area mask," the latter of which denotes areas within the fire perimeter that could not be assessed for
burn severity because the imagery was affected by clouds, cloud shadows, or data gaps. The Key Points
text that describes the proportion of high severity acreage is based on high severity as a percentage of
total assessed acreage (i.e., the total acreage after non-processing area has been excluded). The size
threshold resulted in five states that did not have any reported fires for the time period: Connecticut,
Illinois, New Hampshire, Rhode Island, and Vermont. Puerto Rico is included in Figure 3 totals.
Figure 4. Average Annual Burned Acreage by State, 1984-2014
To create this map, EPA divided the annual acreage burned in each state by the state's total land area.
After doing this for all years during the period of record (1984-2014), EPA calculated an average value
and plotted it on the map. The same five states without fires meeting the size threshold for Figure 3 are
colored gray to indicate insufficient data.
Figure 5. Change in Annual Burned Acreage by State Between 1984-1999 and 2000-2014
To create this map, EPA calculated each state's average annual acreage burned per square mile for the
first half of the record (1984-1999) and the average for the second half (2000-2014). EPA found the
difference between these values and expressed it as a percentage difference (e.g., average annual
acreage during the second half of the record was 10 percent higher than average annual acreage burned
during the first half). The same five states without fires meeting the size threshold for Figure 3 are
colored gray to indicate insufficient data. Changes have been characterized using this method rather
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than measuring a slope over time (e.g., a linear regression) because of the length and shape of the data
set. Visual inspection of the NIFC line in Figure 2 (burned acreage across all states) suggests periods of
relative stability punctuated by a noticeable jump in acreage during the late 1990s. This jump coincides
with a period of transition in certain natural climate oscillations that tend to shift every few decades—
notably, a shift in the Pacific Decadal Oscillation (PDO) around 1998 (Peterson and Schwing, 2003;
Rodionov and Overland, 2005). 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 (Kitzberger et al., 2007; Westerling, 2016). With approximately 30
years of data punctuated by a phase transition, and with research strongly suggesting that the PDO and
other decadal-scale oscillations contribute to cyclical patterns in wildfires in the western United States,
EPA determined that linear regression is not an appropriate method of describing changes over time in
this particular indicator. Instead, EPA chose to simply compare two sub-periods in a manner that
considers all years of data and avoids inferring an annual rate of change. Without a nuanced statistical
analysis to define a break point between two sub-periods, EPA chose to simply break the record into
two periods of roughly equal length: 1984-1999 (16 years) and 2000-2014 (15 years). The fact that the
break point currently lands at 1999 by this method is a coincidence. As more data are added in future
years, the "halfway" break point will move accordingly.
EPA plans to investigate opportunities for a more robust interpretation of state-level trends over time in
future editions of this indicator.
Comparison of Sources
Figure TD-2 compares total wildfire extent estimates from NIFC, Smokey Bear Reports, and MTBS. This
graph shows that MTBS estimates follow the same pattern as the NIFC data set but are always
somewhat lower than NIFC's totals because MTBS excludes small fires. The graph also shows how the
most recent MTBS estimates compare with the MTBS data release used in the previous update to this
indicator. As expected, the data show evidence of revisions to historical data, but the changes are not
extensive.
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Figure TD-2. Comparison of Wildfire Extent from Three Data Sources, 1983-2015
-NIFC
-Smokey Bear Reports
MTBS as of April 2016
2020
Note: These MTBS totals exclude small fires and RX, WFU, and UNKfire types. They include acreage
classified as "non-processing area mask," so they will differ from the totals implied by Figure 3.
Indicator Development
NIFC's website provides data from 1960 through 2015, and Smokey Bear Reports are available from
1917 to 1997. The data available prior to the early 1980s, however, provide incomplete geographic
coverage, as fire statistics at the time were not compiled from the full extent of "burnable" lands. Thus,
Figures 1 and 2 of this indicator begin in 1983, which was the first year of nationwide reporting via ICS-
209 reports. Figures 3, 4, and 5 begin in 1984, which was the first year for which the MTBS project
conducted its detailed analysis. MTBS depends on aerial imagery and the level of detail captured
consistently in ICS reports. Thus, while a longer period of record would be desirable when analyzing
long-term changes in a climatological context, EPA could not extend this indicator with pre-1983 data
without introducing inconsistencies and gaps that would preclude meaningful comparisons over time
and space.
For more discussion regarding the availability, coverage, and reliability of historical wildfire statistics, see
the authoritative discussions in Short (2013) and Short (2015). An accompanying publicly available
seminar (http://videos.firelab.org/ffs/2013-14Seminar/032014Seminar/032Q14Seminar.html) explains
additional nuances and advises users on how they should and should not use the data. Based on these
sources, Table TD-1 summarizes the available data sets, their coverage, and their underlying sources.
NIFC's pre-1983 estimates actually derive from the Smokey Bear Reports (Short, 2015; and publicly
available seminar cited above); therefore, in reality, the Smokey Bear Reports are the only underlying
nationwide source of pre-1983 wildfire statistics.
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Table TD-1. Comparison of Historical Wildfire Data Sources
Data set
Variables
Temporal
range
Resolution
Geographic
coverage
Underlying sources
NIFC
(Figures 1 and 2)
Acreage and
incidence
(number of
fires)
1983-2015
Annual
National
ICS incident reports
NIFC pre-1983
Acreage and
incidence
1960-1982
Annual
National
with gaps
Smokey Bear Reports,
which are based on
estimates submitted
by various agencies
Smokey Bear
Reports
(recent data in
Figures 1 and 2)
Acreage and
incidence
1917-1997
Annual
National
with gaps
Estimates submitted
by various agencies
MTBS
(Figures 3,4, and
5)
Burn
severity;
acreage by
state
1984-2014
Annual
National
ICS incident reports
A fundamental shift in wildfire reporting took place in the early 1980s with the onset of the ICS reporting
system. Prior to this time, reports were submitted to the USDA Forest Service by selected state and
federal agencies, covering land within each agency's jurisdiction. Many of these reports were limited to
fires on land with "protected" status (i.e., land designated for cooperative fire control). Fires occurring
on "unprotected" land would not necessarily be fought, and they would not be counted in the statistics
either. Figure TD-3 below, based on data obtained from the USDA Forest Service (Short, 2015),
demonstrates how the reporting area was well below the total nationwide "burnable" acreage until the
1980s. Increases in the reporting area occurred when additional agencies joined the reporting program.
For example, the Bureau of Land Management began reporting around 1964, which accounts for the
noticeable jump in the blue line in Figure TD-3.
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Figure TD-3. "Smokey Bear Reports" Reporting Area Over Time
K. Short's estimate For total burnable land (c. 2000)
2000
The Smokey Bear Reports achieved essentially complete participation and coverage by the early 1980s.
They continued to be compiled even with the advent of the ICS system around 1983, until being phased
out in the late 1990s. Thus, the Smokey Bear Reports and the ICS reports provide complementary
coverage for much of the 1980s and 1990s. During the first few years of ICS data collection—particularly
1983 and 1984—the Smokey Bear Reports showed much higher fire occurrence than NIFC's ICS-derived
statistics. The USDA Forest Service attributes this difference to the ramp-up and gradual adoption of ICS
nationwide. Other studies such as Dennison et al. (2014) also describe the advantages of using recent,
robust data sets instead of longer, less complete fire databases previously used for trend analysis.
7. Quality Assurance and Quality Control
The ICS-209 form provides clear guidelines for wildfire reporting for state, local, and federal agencies.
These guidelines are accessible on the NIFC website at:
https://gacc.nifc.gov/nrcc/dc/idgvc/dispatchforms/ics209.tips.pdf. The information in the ICS-209 forms
is compiled by the SIT program to provide daily situation reports that summarize wildfire conditions at
state and national levels. This compiled information forms the basis for NIFC summary statistics. The
NIFC does not provide details on how it counts, measures acreage, or filters out the double reporting of
fires, fires that split, fires that merge, incomplete forms, or other potential data irregularities. The
frequency of these confounding factors, however, is likely limited and may not seriously compromise
the quality of the data presented in this indicator.
MTBS standardizes and corrects raw fire incidence data. The project avoids editing source data with the
exception of correcting a record's geospatial coordinates if (1) the coordinates are clearly incorrect, and
(2) a correction can be made with confidence. All selected scenes from the database are ordered and
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processed following existing USGS-EROS protocols. Data obtained from MTBS were also cross-checked
prior to conducting analyses for this indicator.
Analysis	
8.	Comparability Over Time and Space
NIFC methods and statistics have not changed since 1983, and they can be compared on an annual basis
at national scales. The sole exception is the NIFC fire count and burned acreage data points for the year
2004, which are missing totals from state lands in North Carolina. Thus, these two points slightly
compromise the comparability over both time and space. Smokey Bear Reports also used consistent
methods from 1983 to 1997, and they covered the full extent of "burnable" U.S. lands throughout this
period. MTBS has used consistent methods to classify burn severity from 1984 through 2014, allowing
for annual comparisons through time and allowing for spatial comparisons among states. MTBS is based
on a type of satellite imagery that has been collected consistently with sufficient resolution to support
this analysis throughout the period of record.
Figures 4 and 5 were derived from an MTBS data set that uses different size thresholds for different
states. This data set includes fires > 1,000 acres in the western United States and > 500 acres in the
eastern United States. Thus, the map might undercount small fires in the West, compared with the East.
These thresholds have held consistent for each state over time, however, which lends validity to the
analysis of state-level trends over time.
9.	Data Limitations
Factors that may impact the confidence, application, or conclusions drawn from this indicator are as
follows:
1.	Wildfire activity can be influenced by a variety of other factors besides climate. Examples
include changes in human activities and land management strategies overtime, particularly
changes in fire suppression and fire management practices, which (among other things) can
potentially contribute to more damaging fires in the future if they result in a buildup of fuel in
the understory. Grazing activities can also influence the amount and type of vegetation in the
landscape, and changes in land cover and land use—for example, forest to non-forest
conversion—can affect the extent and type of "burnable" land. Thus, further analysis is needed
before an apparent change in wildfire activity can necessarily be attributed to climate change.
2.	The dominant drivers of wildfire activity can vary by region. Contributing factors may include
(but are not limited to) temperatures in specific seasons (particularly spring), drought, and
precipitation that contributes to vegetation growth. As described in Section 6, wildfire trends in
some regions have been linked with certain phases of multi-year and multi-decadal climate
oscillations (Kitzberger et al., 2007; Westerling et al., 2006). Climate patterns that lead to more
wildfire activity in some parts of the United States may lead to a simultaneous decrease in
activity in other regions (e.g., the Northwest versus the Southwest). Reconstructions based on
tree rings can provide hundreds of years of context for understanding such patterns and how
they vary regionally (e.g., Swetnam and Betancourt, 1998).
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3.	While this indicator is officially limited to "wildland" fires, it includes fires that encroach on—or
perhaps started in—developed areas at the wildland-urban interface (WUI). Encroachment of
the WUI over time into previously wild lands could influence trends in wildfire frequency and
extent (Radeloff et al., 2005).
4.	NIFC data, which are derived from government entities of varying scope or jurisdiction, can be
limited by inconsistencies across how data are reported through ICS-209 forms. With
aggregation from so many potential sources, wildfire incidence data, particularly historical data,
may be redundant or erroneous. Data aggregation among sources may result in variability in
reporting accuracy and protocol.
5.	The MTBS program depends on certain conditions to make accurate measurements of burn
severity:
•	Accurate fire location coordinates that match burn scars visible via satellite.
•	Accurate fire size information that ensures that fires meeting the MTBS size criteria are
properly included.
•	Accurate date of ignition and out date that guide the appropriate selection of imagery,
particularly for baseline assessments.
•	Pre-fire and post-fire images that are cloud-free to avoid visual obscuration of the fire area.
6.	Some fires of very low severity may not be visible in the satellite imagery and therefore
impossible to delineate or characterize. Cloud cover, cloud shadow, or data gaps can also
preclude damage assessment. To account for all of these limitations, the MTBS project includes
a burn severity classification of "non-processing area mask." This classification accounts for
approximately 5.4 percent of the total wildfire acreage from 1984 through 2014.
10.	Sources of Uncertainty
Uncertainties in these data sets have not been quantified. The most likely sources of uncertainty relate
to initial data collection methods. Federal land management agencies have varying standards for
content, geospatial accuracy, and nomenclature. Duplicate records occur due to reporting of a given
incident by multiple agencies, such as redundant reports from local, state, or federal entities. In any
given year, as much as three-quarters (or more) of all fire incidents are reported by non-federal state
and local agencies (NICC, 2015). Cases of gross geospatial inaccuracies may also occur. Similar
inconsistencies occur within state databases; however, the MTBS project addresses issues such as
duplicates and nomenclature during pre-processing.
11.	Sources of Variability
Forest conditions, and therefore wildfire incidents, are highly affected by climate conditions. In addition
to year-to-year variations, evidence suggests that wildfire patterns in the western United States are
influenced by multi-year and multi-decadal climate oscillations such as the PDO
(http://iisao.washington.edu/pdo) and the Atlantic Multidecadal Oscillation
(www.aoml.noaa.gov/phod/amo faq.php). For example, see Kitzberger et al. (2007) and Westerling
(2016) for discussion of warmer, drier conditions that have contributed to increases in wildfire activity in
certain regions.
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Changes in the frequency of wildfire triggers (e.g., lightning, negligent or deliberate human activity)
could also affect wildfire frequency. Burn severity is affected by local vegetation regimes and fuel loads.
Finally, improvements or strategic changes in firefighting and fire management may affect wildfire
prevalence and resulting damages. Forest management practices have changed over time from
complete fire suppression to controlled burns. These varied approaches and the extent to which they
are applied on state or regional levels can influence the wildfire data presented in this indicator.
12. Statistical/Trend Analysis
As described in Section 6, the nature of this topic and the length and shape of the time series suggest
that linear regression is not a suitable tool for characterizing long-term trends and their significance.
Thus, the figures and Key Points do not report regression results. Ordinary least-squares linear
regressions from the NIFC data set have been calculated here, just for reference. Regression slopes and
p-values are indicated in Table TD-2 below.
Table TD-2. Wildfire Regression Statistics
Indicator component
Regression slope
P-value
NIFC fire frequency (Figure 1)
+393 fires/year
0.24
NIFC burn acreage (Figure 2)
+192,003 acres/year
<0.001
References
Dennison, P.E., S.C. Brewer, J.D. Arnold, and M.A. Moritz. 2014. Large wildfire trends in the western
United States, 1984-2011. Geophys. Res. Lett. 41(8):2928-2933.
Fire and Aviation Management and Predictive Services. 2009. Interagency wildland fire incident
information reporting application (SIT-209). www.predictiveservices.nifc.gov/intelligence/SIT-
209 Bus Req Final vla.pdf.
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.
MTBS (Monitoring Trends in Burn Severity). 2005. Report on the Pacific Northwest and Pacific Southwest
fires. www.mtbs.gov/files/MTBS pnw-psw final.pdf.
NICC (National Interagency Coordination Center). 2015. Wildland fire summary and statistics annual
report, www.predictiveservices.nifc.gov/intelligence/2014 Statssumm/annual report 2014.pdf.
NWCG (National Wildfire Coordinating Group). 2015. Glossary of wildland fire terminology. Updated
October 2015. www.nwcg.gov/glossarv-of-wildland-fire-terminology.
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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Radeloff, V.C., R.B. Hammer, S.I. Stewart, J.S. Fried, S.S. Holcomb, and J.F. McKeefry. 2005. The wildland-
urban interface in the United States. Ecol. Appl. 15:799-805.
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Bering Sea ecosystem. ICES J. Mar. Sci. 62:328-332.
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data. Int. J. Wildland Fire 24(7):883-891.
Swetnam, T.W., and J.L. Betancourt. 1998. Mesoscale disturbance and ecological response to decadal
climatic variability in the American Southwest. J. Climate 11:3128-3147.
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.
Westerling, A.L., H.G. Hidalgo, D.R. Cayan, and T.W. Swetnam. 2006. Warming and earlier spring
increase western U.S. forest wildfire activity. Science 313(5789):940-943.
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