Study: Vast majority of wildfires started by humans

The devastating wildfires that tore through Gatlinburg, Tennessee, in December were extraordinary – they left 14 people dead and injured another 175.

But they were also typical wildfires in one way: Authorities say they were caused by humans.

According to a NASA-funded study published in the Proceedings of the National Academy of Sciences in February, 84% of wildfires in the United States are caused by people.

The study, by University of Colorado Boulder professor Jennifer K. Balch and other colleagues, examined government agency wildfire records from 1992-2012. It is one of the largest projects of its kind.

The analysis found that human-started wildfires have tripled the length of the wildfire season and accounted for a total of 44% of all acreage burned. Lightning-sparked wildfires are mostly concentrated in summer, but human activity has expanded the fire season to include spring and fall.

Range of causes for wildfires

Wildfires caused by people start from a variety of sources, including campfires, smoking, fireworks, and arson, the study found.

Two juveniles face charges of aggravated arson in connection with the Gatlinburg blazes – which happened in December – well outside the natural wildfire season.

The most common day of the year for human-started fires is July 4, when the use of fireworks and barbecues are widespread. The study produced a map showing the areas most affected by human-caused wildfires over the past two decades.

It shows those fires were most concentrated in the Appalachian mountains and in California, as well as in Minnesota along the United States’ northern border and in Texas along its southern border.

Several wildfires broke out in Texas, Oklahoma, Kansas, and Colorado on Monday in separate incidents. Though officials had not yet determined their causes, the study goes some way to predicting what their analysis might soon be.