CLIMATE MODELS PROJECT INCREASE IN U.S. WILDFIRE RISK
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.
he 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.
