SCIENTISTS using satellite data and climate models from the National Aeronautics & Space Administration (NASA) have projected that drier conditions likely will cause increased fire activity across the U.S. in coming decades.
Other findings about U.S. wildfires, including their carbon emissions and how the length and strength of fire seasons are expected to change under future climate conditions, were also presented at the annual meeting of the American Geophysical Union in San Francisco, Cal.
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 U.N. Intergovernmental Panel on Climate Change -- to examine how dryness and, therefore, fire activity are expected to change.
The researchers calculated results for low and high greenhouse gas emission 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.
Through August of this year, the burned area of the U.S. topped 6.17 million acres, according to a fire emissions database that incorporates burned area estimates generated from observations by the Moderate Resolution Imaging Spectroradiometer instruments on NASA's Aqua and Terra satellites. That is short of the record 7.90 million acres burned in 2011 but exceeds the area burned during 12 of the 15 years since recordkeeping began in 1997.
From a fire and emissions management perspective, wildfires are not the entire story, according to research by Hsiao-Wen Lin of the University of California-Irvine. Satellite data show that agricultural and prescribed fires are a significant factor and account for 70% of the total number of active fires in the continental U.S.
Agricultural fires have increased 30% in the last decade, Lin added, but, in contrast with wildfires, agricultural and prescribed fires are less affected by climate -- especially drought -- during the fire season.
Managed fire benefits
Regardless, with the current focus on how carbon emissions affect climate change and the critical role forests play in storing carbon, policy-makers need a better understanding of the effect fire has on the global carbon cycle, according to Matthew Hurteau, a researcher in The Pennsylvania State University's College of Agricultural Sciences.
As carbon registries, carbon credits and carbon trading become more important in the coming years, managed fire should play a major role in managing forests for both ecological and carbon sequestration reasons, Hurteau, an assistant professor of forest resources, said.
Hurteau said he is seeking to alter perspectives about the effect fire has on carbon sequestration. His research has involved both field studies and modeling to address a range of topics, including forest carbon, wildfires, species diversity and productivity.
"We are losing the fire-suppression battle because we have such a huge accumulation of fuel on many forest floors in the West," he said. "Fuel accumulation, combined with more extended droughts and higher temperatures, result in much longer, more severe fire seasons. We are seeing a substantial increase in the amount of land area burned over time."
That matters because forest fires release carbon into the atmosphere, Penn State said. However, Hurteau's research indicates that more fires -- albeit managed and less severe -- combined with thinning stands of trees, actually benefit carbon markets because the amount of carbon locked up by forests that are managed with prescribed fire is greater.
"It is a question of having less frequent but really large fires or more frequent but smaller prescribed burns," he explained. "The difference between those two is the severity of the fire. These huge, severe wildfires we have been seeing kill most of the trees involved because the flames don't only touch the surface of the forest, but they also burn up into the canopy."
However, Hurteau added, "with a more frequent fire regime, we have surface fire that is not burning nearly as hot and is not getting up into the canopy, resulting in much lower tree mortality. So, overall, more frequent but less severe fires give off less carbon, but more importantly, more of the carbon is locked up in surviving trees that will continue to grow and sequester more carbon."
Hurteau hopes his recent research article, "Aligning Ecology & Markets in the Forest Carbon Cycle," published this fall in the journal Frontiers in Ecology & the Environment, will further the discussion that prescribed fire is beneficial for both ecological and carbon sequestration purposes.
"The ability of forests to sequester carbon dioxide from the atmosphere has captured the attention of policy-makers, non-governmental organizations and a burgeoning number of (carbon) offset project developers," he said. "The underlying concept is simple: Sequester carbon from the atmosphere by reforesting degraded lands, thereby increasing the amount of carbon stored in current forests or reducing forest loss."
Hurteau said he believes that classifying tree stand thinning and prescribed burning as forest degradation is misguided and needs to change.
"When we get fixated on mitigating climate change and we look at a forest as just a place to store carbon -- if that becomes our primary objective -- it's a mistake," he said. "What we really should be doing is managing these systems based on their ecology and looking at carbon sequestration as an ancillary service that the ecosystem provides."