Causes of Wildfires in the United States

Caitlin Dempsey

Updated:

Wildfires are an important component of the natural process across the geography of the United States. Between 2013 and 2022, the United States experienced an average of 61,410 wildfires annually that burned an average of 7.2 million acres.

For some ecosystems like chaparral, regular wildfires are required for the health of local ecosystems by releasing stored nutrients to the soil, and some plants require scarification from fire in order to sprout.

Climate change, however, is fueling an increase in the severity and frequency of wildfires in many areas of the United States.

Wildfires can be also be destructive natural disasters that can burn through thousands of acres, destroying the natural environment, houses, and even killing people.


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Where do wildfires happen in the United States?

The majority of wildfires occur in the Western United States, primarily in California, Arizona, Nevada, New Mexico, and Oregon.

These states encompass a diverse set of landscapes, including dense forests, scrublands, and grasslands, each presenting unique conditions conducive to wildfires.

California, for example, experiences a climate in many parts of the state that has high temperatures and low rainfall during the summer months. Many of the vegetation communities have adapted to a natural cycle of fires.

Fire and embers glow orange on the floor of a conifer forest at twilight.
A wildfire burns among the conifers in the Sierra Nevada in October of 2018. Photo: Sequoia and Kings Canyon National Parks, NPS/Rebecca Paterson, public domain.

The chaparral biome, characterized by dense, shrub-filled landscapes and known for its fire ecology, is prevalent in this region. The region’s Santa Ana Winds further exacerbate the wildfire risk, propelling fires across vast areas.

The Southeastern United States, particularly Florida and the coastal plains of Georgia and South Carolina, also experiences wildfires, although they differ in nature. Here, the prevalence of grasslands and swamps combined with lightning strikes during thunderstorms leads to a different fire regime.

NASA reports that in any given year, half of the fires in the United States originate in the Southeastern United States. Most of these fires that occur throughout Florida, Georgia, South Carolina, Alabama, and Mississippi are the result of land management fires — with fires started in order to burn fields in preparation for the next planting.

Alaska is another hotspot for wildfires. In 2022, a total of 68,988 U.S. wildfires burned 7.6 million acres, with Alaska accounting for 40% of the affected acreage – for a total of 3.1 million acres.

Natural Causes of Wildfires

Wildfires in the United States have long been a natural component of the cycle of forest ecosystems. Natural causes of fires include lightning strikes, lava flows, and spontaneous combustion.

Lightning strikes on dry ground is the most common cause of fires in the southeast part of the United States and in the dry Rocky Mountain region.

Drought, heat, fire suppression (which leads to a buildup of fuel in the form of dead vegetation), and strong winds all contribute to the intensity and potential devastation of a wildfire.

A tree burning in the North wildfire in Sequoia and Kings Canyon National Parks in 2004.
North wildfire, Sequoia and Kings Canyon National Parks, Summer 2004. Photo: NPS, public domain.

Human Causes of Wildfires

The National Park Service in the United States estimates that human activity causes approximately 85% of wildfires each year.

In 2012, for example, the Natural Interagency Fire Center found that people were responsible for 58,331 fires, compared to 9,443 fires initiated by lightning strikes.

Map showing the percentage of wildfires caused by humans in the United States.
The majority of wildfires in the United States are started by humans, not by lightning. Map showing the percentage of wildfires caused by humans in the United States. Map: NASA using data from Balch, J. et al., 2017.

The actual geographic area burned by natural versus human-caused fires varies greatly: while lightning strikes accounted for only 14 percent of all flames in 2012, they burned a total of 6,825,989 acres, compared to 2,500,249 acres destroyed by human-caused fires.

Campfires, trash burning, cigarettes, sparks from passing trains and cars, and arson all contribute to human-caused wildfires.

Other manmade causes of wildfires can include intentional arson, sparks from railroad tracks, and downed electrical lines.

In California, the Pacific Northwest, and the forests of the eastern part of the United States, manmade causes resulted in 80% of the wildfires. Although places like Florida have a lot of thunder storms and lightning strikes, 60-80% of fires in this region were started from manmade causes.

Unfortunately, the human element of wildfires has caused the wildfire season across the country to lengthen and become even more dangerous than ever before.

Wildfire Seasons in the United States are Lengthening

Wildfires tend to stay in the dry summer months, but there has been an increase in wildfires occurring in the spring, fall, and winter. The fire season differs depending on where in the United States you live, but the wildfire risk is staying higher for more months out of the year.

Wildfires have caused more damage on average since 1992. As the climate changes, forests and other areas are drying out faster and staying dry for longer. This eliminates a helpful protective barrier of moisture that can protect forests and agricultural areas from natural and manmade wildfires.

Manmade wildfires usually start relatively close to population centers, which means they only burn about 44% of the total wildfire damaged zones every year. Their location can allow firefighters to get to these wildfires quicker and put them out before they can grow to unmanageable size. This can also mean that fires pose a greater risk to cities and towns in the path of these fires.

How Wildfires Spread and Intensify

A wildfire’s intensity and geographic spread are influenced by three elements.

The first consideration is the amount of fuel available. Fuel is collected debris in a natural region such as fallen tree limbs, needles, leaves, and other combustible substances. The longer the time between flames, the more dead organic stuff accumulates.

A building is wrapped in heat-reflecting materials to protect it from a wildfire.  Photo: NPS, public domain.
A building is wrapped in heat-reflecting materials to protect it from a wildfire. Photo: NPS, public domain.

Wetter-than-average months, which promote increased vegetation growth, followed by a drought season, can also increase the amount of dry materials accessible to burn.

Second, weather conditions might increase the chance of a fire. In California, for example, wildfires are more likely to occur during the hot and dry summer months than during the wet and cold winter months.

Wind conditions can significantly increase the intensity and speed with which a fire spreads.

Finally, topography influences the spread of a fire. Fire spreads more quickly when traveling down a steep hill than it does across a flat plain.

One of the Most Devastating Recorded Wildfire in the U.S.

One of the most devastating wildfires in the history of the United States occurred on October 8, 1871 in the Peshtigo, Wisconsin area.  

A cold front that blew in from the West fanned small forest clearing fires out of control.  The ensuring firestorm, coupled with a drier than usual season, ignited an inferno.

A bird's eye view map of Peshtigo, Wisconsin published one month before the great fire.
A bird’s eye view map of Peshtigo, Wisconsin published one month before the great fire. Map: T.M. Fowler & Co., September 1871, Library of Congress.

The fire burned through an area of 1,875 square miles and destroyed the towns of Peshtigo and Brussels.  Between 1,200 and 2,500 people are estimated to have lost their lives.  

This wildfire occurred on the same day as the Great Chicago Fire and subsequently, attention and aid to the area was overshadowed by that fire event which took 250 lives.

Great Fire of 1910

The Great Fire of 1910, which raged for two days from August 20–21, 1910, devastated about 3,000,000 acres, making it one of North America’s largest wildfires on record at the time.

Drought and high temperatures allowed sparks from railroads, lightning strikes, and backfire crews to start an estimated 1,000 to 3,000 fires across Idaho, Montana, Washington, and British Columbia.

The fire killed 89 people and burned the Idaho towns of Falcon and Grand Forks, as well as the Montana communities of De Borgia, Haugan, Henderson, Taft, and Tuscor.

Devastating fires, such as the Great Fire of 1910, inspired a new era in forest management in the United States.

Yellowstone Fires of 1988

1.2 million acres were burned during the summer of 1988, one of the greatest group of wildfires in Yellowstone National Park’s history, with 793,000 (approximately 36 percent) of the park’s 2,221,800 acres charred.

In the larger Yellowstone area, 248 fires were ignited, with several significant fires accounting for more than 95 percent of the burned acreage.

An elk stands among the charred trees during the 1988 Yellowstone fires.  Photo: NPS, public domain.
An elk stands among the charred trees during the 1988 Yellowstone fires. Photo: NPS, public domain.

In 1988, the months of April and May had more rain than usual, followed by a severe drought in June. Dry fuels and high winds created an ideal environment for powerful fires sparked by lightning strikes, which burned out of control until September 11, 1988, when the first snowfall helped to put a stop to the wildfires.

The 1988 wildfires prompted a review of existing fire management practices in the United States, allowing forestry officials to better understand the trade-off between fire suppression and allowing natural fires to burn.

Every year, thousands of wildfires rage across the United States, consuming millions of acres. Natural phenomena such as lightning strikes, as well as human activity such as garbage burning, campfires, and arson, create wildfires.

References

Ahrens, M. (2013, June). Lightening Fires and Lightening Strikes. NFPA. https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/US-Fire-Problem/Fire-causes/oslightning.ashx?la=en

Balch, J. K., Bradley, B. A., Abatzoglou, J. T., Nagy, R. C., Fusco, E. J., & Mahood, A. L. (2017). Human-started wildfires expand the fire niche across the United StatesProceedings of the National Academy of Sciences114(11), 2946-2951.

Biondich, S. (2010, June 9). The great Peshtigo fire. Shepherd Express. https://shepherdexpress.com/news/happening-now/great-peshtigo-fire/

Burke, M., Driscoll, A., Heft-Neal, S., Xue, J., Burney, J., & Wara, M. (2021). The changing risk and burden of wildfire in the United States. Proceedings of the National Academy of Sciences118(2), e2011048118. https://doi.org/10.1073/pnas.2011048118

Fire. (n.d.). Yellowstone National Parkhttps://www.nps.gov/yell/learn/nature/fire.htm

The Great Fire of 1910. (n.d.). US Forest Service. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5444731.pdf

Voiland, A. (2017, March 7). People cause most U.S. wildfires. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/89757/people-cause-most-us-wildfires

Wildfire causes and evaluations (U.S. National Park Service). (2018, November 27). NPS.gov (U.S. National Park Service). https://www.nps.gov/articles/wildfire-causes-and-evaluation.htm

Wildfire Statistics. (2023, June 1). Congressional Research Service. https://sgp.fas.org/crs/misc/IF10244.pdf

This article was originally written on October 28, 2017 and has since been updated.

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.