Scientists using NASA satellite images and carbon dioxide models say drier conditions across the center and eastern parts of the United States will exacerbate wildfire risk over the next 40 years.

Through the middle of the century, the United States will see an increase in the area burned by fires, as well as drier conditions in the Great Plains through the Dakotas and the East. Areas where fire is used for agriculture and forestry will be at the greatest risk, said Doug Morton, a physical scientist at NASA's Goddard Space Flight Center.

In the future, using fire to control fields or forests "would present a risk for wildfire where today it would be less of an issue," he said.

High fire years like the past two years would likely occur two to four times per decade by midcentury. Under current climate conditions, these extreme events occur about once per decade.

The study, which relied on observational satellite data from 1984 to 2008 with a carbon cycle model, was prepared for consideration in the fifth assessment report from the Intergovernmental Panel on Climate Change, to be released next year.

The researchers looked at regional sensitivity, variations in the fire season and how the results might indicate the frequency of extreme events. Precipitation levels, as well as higher overall temperatures and heat waves, will be the most important climate variables, Morton said.

Changes in climate have already changed the seasonality of fires, said Steve Running, a wildfire expert at the University of Montana. In Billings, Mont., fires have started in January in the past few years due to the lack of winter snowpack, he said at a briefing last week on Capitol Hill.

This year, the U.S. burned area topped 2.5 million hectares (6.2 million acres), according to NASA.

The results of this study incorporated carbon emissions sources that had not frequently been used before, said Chris Williams, an assistant professor of geography at Clark University and contributor. These included the carbon emissions from "killed" biomass that lies decomposing in forests after fire, and the rate of forest growth that indicates how well an area will absorb carbon over time.

"A lot of studies in the past tried to address carbon consequences solely on direct combustion," said Williams, referring to the carbon released into the atmosphere through burning itself.

The research was presented at the American Geophysical Union's annual meting in San Francisco.