PORTLAND, Ore. June 26, 2009. The recent
increase in area burned by wildfires in the Western United States
is a product not of higher temperatures or longer fire seasons
alone, but a complex relationship between climate and fuels that
varies among different ecosystems, according to a study conducted
by U.S. Forest Service and university scientists. The study is
the most detailed examination of wildfire in the United States
to date and appears in the current issue of the journal Ecological
“ We found that what matters most in accounting for large
wildfires in the Western United States is how climate influences
up—or production—and drying of fuels,” said Jeremy
Littell, a research scientist with the University of Washington’s
Climate Impacts Group and lead investigator of the study. “Climate
affects fuels in different ecosystems differently, meaning that
future wildfire size and, likely, severity depends on interactions
between climate and fuel availability and production.”
To explore climate-fire relationships, the scientists used fire
data from 1916 to 2003 for 19 ecosystem types in 11 Western States
to construct models of total wildfire area burned. They then compared
these fire models with monthly state divisional climate data.
The study confirmed what scientists have long observed: that low
precipitation and high temperatures dry out fuels and result in
significant fire years, a pattern that dominates the northern and
mountainous portions of the West. But it also provided new insight
on the relationship between climate and fire, such as Western shrublands’ and
grasslands’ requirement for high precipitation one year followed
by dry conditions the next to produce fuels sufficient to result
in large wildfires.
The study revealed that climate influences the likelihood of large
fires by controlling the drying of existing fuels in forests and
the production of fuels in more arid ecosystems. The influence
of climate leading up to a fire season depends on whether the ecosystem
is more forested or more like a woodland or shrubland.
“ These data tell us that the effectiveness of fuel reductions in reducing
area burned may vary in different parts of the country,” said David L.
Peterson, a research biologist with the Forest Service’s Pacific Northwest
Research Station and one of the study’s authors. “With this information,
managers can design treatments appropriate for specific climate-fire relationships
and prioritize efforts where they can realize the most benefit.”
Findings from the study suggest that, as the climate continues to warm, more
area can be expected to burn, at least in northern portions of the West, corroborating
what researchers have projected in previous studies. In addition, cooler, wetter
areas that are relatively fire-free today, such as the west side of the Cascade
Range, may be more prone to fire by mid-century if climate projections hold and
weather becomes more extreme.
To read the study online, visit http://www.esajournals.org/doi/pdf/10.1890/07-1183.1.