Large wildfires in the United States burn more than twice the area they did in 1970, and the average wildfire season is 78 days longer.
Research shows that changes in climate, especially earlier snowmelt due to warming in the spring and summer, have led to hot, dry conditions that boost this increase in fire activity in some areas. For much of the U.S. West, projections show that an average annual 1 degree Celsius temperature increase would increase the median burned area per year as much as 600 percent in some types of forests.
Although land use and firefighting tactics can play a role in lowering or raising risks, observed and anticipated changes in climate are expected to continue to increase the area affected by wildfires in the United States.
Wildfire risk depends on a number of factors, including temperature, soil moisture, and the presence of trees, shrubs, and other potential fuel. All these factors have strong direct or indirect ties to climate variability and climate change.
Once a fire starts – more than 80 percent of U.S. wildfires are caused by people – warmer temperatures and drier conditions can help them spread and make them harder to put out. Warmer, drier conditions also contribute to the spread of the mountain pine beetle and other insects that can weaken or kill trees, building up the fuels in a forest.
Threats Posed by Wildfires
Since 2000, 11 forest fires in the United States have caused at least $1 billion in damages each, mainly from the loss of homes and infrastructure, along with firefighting costs.
- The 2017 wildfire season is well above average, with deadly fires in California and throughout the West, including Montana, Oregon, and Washington state.
- In 2015, wildfires burned more than 10 million acres across the United States, half of that in Alaska alone. It was the highest annual total acreage burned since record-keeping began in 1960. The costliest fires occurred in California, where more than 2,500 structures were destroyed in the Valley and Butte wildfires.
- Wildfires burned more than 9 million acres in 2012. Colorado’s two most destructive fires ever – the Waldo Canyon and High Park fires – happened during this particularly destructive season.
- In 2011, the Las Conchas Fire in New Mexico became the state’s largest in history by a factor of three. In 2012, that record was broken as the Whitewater-Baldy Complex fire burned nearly twice as many acres as the Las Conchas Fire.