Causes of Wildfires in the US

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Approximately 84% of wildfires in the United States that required help by firefighters between 1992 and 2012 were caused by humans according to a recent study. Discarding cigarettes, unattended campfires, and losing control of controlled burns were three of the most common manmade causes of wildfires. Unfortunately, the human element of wildfires has caused the wildfire season across the country to lengthen and become even more dangerous than ever before.

In terms of natural causes, wildfires can be caused by lightning strikes on dry ground. This is the most common cause of fires in the southeast part of the United States and in the dry Rocky Mountain region. 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.

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. 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.

Map showing the percentage and frequency of fires caused by humans. Map: Joshua Stevens, using fire data courtesy of Balch, J. et al. (2017).
Map showing the percentage and frequency of fires caused by humans. Map: Joshua Stevens, using fire data courtesy of Balch, J. et al. (2017).

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.

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


People Cause Most U.S. Wildfires.  Earth Observatory, NASA.

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.



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