Simultaneous large wildfires will increase in Western U.S.

The scientists began their analysis by drawing on observations of fires that burned in recent decades across the Western United States, dividing the blazes into regions, known as Geographic Area Coordination Centers, that are used for many fire management decisions. They correlated the fires with observations of atmospheric conditions, including temperature, precipitation, humidity, and surface winds.  

The research team then simulated how those conditions will change as the climate warms this century. To do so, they turned to a set of advanced regional and global climate models, including simulations from the NCAR-Wyoming Supercomputing Center. By applying statistical techniques to the resulting simulations, the scientists were able to infer the risk of simultaneous wildfires in Geographic Area Coordination Centers across the West.

The results showed a steady increase in simultaneous fires across all regions of the West throughout this century, with more blazes burning in both relatively moderate and severe seasons. The trend was particularly pronounced for the most severe wildfire seasons — those that currently occur only every 10 years on average. In the future, such seasons may be expected to occur at least twice as often, and up to nearly five times per decade in the northern Rocky Mountains, which was the most affected region.

In addition, as hot and dry conditions become more conducive for wildfires, the peak seasons for simultaneous blazes in various regions will become as much as several weeks longer by the end of the century. This can be critically important for firefighting, since crews and equipment are often moved around the country (or even between the United States and other nations, such as Australia) to fight fires as different regions undergo their own peak seasons.

The study assumed that society would emit high amounts of greenhouse gases into the atmosphere in the future, a scenario known as RCP 8.5. However, even if society were to reduce greenhouse gas emissions, the authors said that would make little difference through mid-century, which is about as far out as policy makers would plan for.

McGinnis said decision-makers can take steps to manage the future risk and impact of simultaneous fires. These range from thinning forests and conducting prescribed burns to increasing firefighting crews and equipment. Such policies, however, can take a number of years to implement, and the strain on resources created by simultaneous fires can affect the ability to conduct prescribed burns and pursue other preventative action.

“We designed this study to be operationally relevant,” McGinnis said. “The findings about long-term trends can be useful to policy makers to inform their decisions on what to do on longer-term policy questions.”

David Hosansky manages media relations at UCAR. The article was originally posted to the website of UCAR.