A firefighter battles the Blue Cut wildfire near Cajon Pass, north of San Bernardino, Calif., on Aug. 16. Ringo Chiu/Agence France-Presse — Getty Images

The sharp increase in fire damage has been attributed to the warming climate, fire-management tactics and the nonstop construction of homes in fire-prone areas.

The Average Size of Wildfires Has Increased Drastically

100 acres 75 10 year rolling average of wildfire size. 50 25 0 1975 1985 1995 2005 2015 100 acres 75 10 year rolling average of wildfire size. 50 25 0 1985 1975 1995 2005 2015 Source: National Interagency Fire Center

The size of wildfires has grown steadily for more than 30 years. In 1982, the average fire covered less than 25 acres. Today, the average wildfire burns about 100 acres.

Scott L. Stephens, a professor of fire science at the University of California, Berkeley, said the widespread practice of suppressing smaller fires had caused some forests to become “predisposed to larger events.”

“When you take fire out of a system for 100 years,” he said, “you change things drastically.”

Large Fires Are Widespread

​The Range of U.S. Wildfires for 2016, as of Aug 17 Ore. Idaho S.D. Wyo. Hot Pot Fire 122,292 acres Neb. CaliF. Utah Denver Kan. Nev. Anderson Creek Fire 397,000 acres Colo. Blue Cut Fire 30,000 acres Ariz. Los Angeles Oklahoma City Okla. Phoenix N.M. Texas Ca WY Anderson Creek Fire 397,000 acres Hot Pot Fire 122,292 acres Blue Cut Fire 30,000 acres TX Source: U.S. Geological Survey, NASA MODIS

This year’s fire season started strong: The number of acres burned by May 20 was 46 percent above average, according to the National Interagency Fire Center. But a wet and cool late May was reflected in the center’s Aug. 17 report, which showed the acreage burned to be around 80 percent of the 10-year average for this point in the year.

“All it takes is a single lightning strike to change the course of the whole season,” said LeRoy Westerling, a professor of forest management at the University of California, Merced.

He said that the calm May period had allowed many grasses and other fuel sources to accumulate, which could cause larger and longer fires this season or next.

Fire Seasons Are Now Longer and More Expensive

$2.0 billion Amount spent on fighting fires by the Department of Interior and the U.S. Forest Service. 1.5 1.0 0.5 0 1986 1990 1995 2000 2005 2010 2015 Amount spent on fighting fires by the Department of Interior and the U.S. Forest Service. $2.0 billion 1.5 1.0 0.5 2015 1986 1995 2005 Source: National Interagency Fire Center

The annual wildfire season is stretching over more of the year, according to Professor Westerling, and the longer the fires last, the more money they cost to control. The federal government spent $202.8 million to fight fires in 1986. Last year, it spent $2.1 billion.

One cause of the longer seasons is environmental: The warming climate has melted snowpacks earlier, increasing the length of time that forests dry out and become vulnerable to burning.

Forest management techniques, like intentional burning and thinning of forests, can help the ecosystem return to a more natural equilibrium, Professor Stephens said, and this would reduce the number of large, destructive fires.

He estimates that California needs at least 10 times the current amount of intentional burns and other forest management efforts to recover the ecosystem balance.

More Homes in Wildland Areas Means More Risk

Hills scorched by a wildfire in June in Calabasas, Calif. Michael Owen Baker/Agence France-Presse — Getty Images

Another factor is people. “Fires are getting expensive as people are building homes further into fire territory,” said Chris Wilcox, the fire director of the United States Fish and Wildlife Service.