Climate models project increase in US wildfire risk

Press release 12-419

Washington -- Scientists using NASA satellite data and climate models  have projected drier conditions likely will cause increased fire activity across the United States in coming decades. Other findings  about U.S. wildfires, including their amount of carbon emissions and  how the length and strength of fire seasons are expected to change  under future climate conditions, were also presented Tuesday at the  annual meeting of the American Geophysical Union in San Francisco.

Doug Morton of NASA's Goddard Space Flight Center in Greenbelt, Md.,  presented the new analysis of future U.S. fire activity. The analysis  was based on current fire trends and predicted greenhouse gas  emissions.

"Climate models project an increase in fire risk across the U.S. by  2050, based on a trend toward drier conditions that favor fire  activity and an increase in the frequency of extreme events," Morton  said.

The analysis by Morton and colleagues used climate projections,  prepared for the Fifth Assessment Report of the United Nations  Intergovernmental Panel on Climate Change, to examine how dryness,  and therefore fire activity, is expected to change.

The researchers calculated results for low and high greenhouse gas  emissions scenarios. In both cases, results suggest more fire seasons  that are longer and stronger across all regions of the U.S. in the  next 30-50 years. Specifically, high fire years like 2012 would  likely occur two to four times per decade by mid-century, instead of  once per decade under current climate conditions.

Through August of this year, the U.S. burned area topped 2.5 million  hectares (6.17 million acres), according to a fire emissions database  that incorporates burned area estimates produced from observations by  the Moderate Resolution Imaging Spectroradiometer instruments on  NASA's Aqua and Terra satellites. That is short of the record 3.2  million hectares (7.90 million acres) burned in 2011, but exceeds the  area burned during 12 of the 15 years since record keeping began in  1997. This and other satellite records, along with more refined  climate and emissions models, are allowing scientists to tease out  new information about fire trends.

"Fire is an inherently global phenomenon, and the only practical way  to track large-scale patterns and changes in fire activity is with  satellites," says Louis Giglio of the University of Maryland at  College Park and Goddard.

As the U.S. land area burned by fire each year has increased  significantly in the past 25 years, so too have the emissions. Carbon  dioxide emissions from wildfires in the western U.S. have more than  doubled since the 1980s, according to Chris Williams of Clark  University in Worcester, Mass.

The satellite-based view allowed Williams and his colleagues to  quantify how much carbon has been released from fires in the U.S.  West. The team used data on fire extent and severity derived from  Landsat satellites to calculate how much biomass is burned and  killed, and how quickly the associated carbon was released to the  atmosphere. The team found carbon emissions from fires have grown  from an average of 8 teragrams (8.8 million tons) per year from 1984  to 1995 to an average of 20 teragrams (22 million tons) per year from  1996 to 2008, increasing 2.4 times in the latter period.

"With the climate change forecast for the region, this trend likely  will continue as the western U.S. gets warmer and drier on average,"  Williams said. "If this comes to pass, we can anticipate increased  fire severity and an even greater area burned annually, causing a  further rise in the release of carbon dioxide."

Researchers expect a drier and more wildfire-prone U.S. in future  decades. Previous research confirmed the connection between the measure of an environment's potential evaporation, or dryness, and  fire activity.

From a fire and emissions management perspective, wildfires are not  the entire U.S. fire story, according to research by Hsiao-Wen Lin of  the University of California at Irvine. Satellite data show  agricultural and prescribed fires are a significant factor and  account for 70 percent of the total number of active fires in the  continental U.S. Agricultural fires have increased 30 percent in the  last decade.

In contrast with wildfires, agricultural and prescribed fires are less affected by climate, especially drought, during the fire season.

"That means there is greater potential to manage fire emissions, even  in a future, drier climate with more wildfires. We need to use cost-benefit analysis to assess whether reductions in agricultural fire emissions -- which would benefit public health -- would significantly impact crop yields or other ecosystem services," Lin said.