Wildfires Studied

This study refines a lot of what we think we know about wild fires and the like. If there is a take home here, it is that fire requires fuel. Therefore a succession of moist years will produce a large supply of fuel and the resultant firestorm when the inevitable dry year shows up.

It makes the attempt to link wild fires with climate change even sillier that I originally thought. Record breaking forest fires are only possible if preceded by record breaking fuel production.

The only way man can affect the cycle at all is to suppress fires and encourage a build up of fuel until the fire is unstoppable.

Dry summers happen everywhere, even in the Northwest rainforest where I reside. I recall getting real nervous one summer when I lived right beside old growth timber that was loaded with dry waste. It is a little like sitting beside a trail of black powder and playing with matches. Yet we build there.

The arid west is actually as bad as it can get. Every year a batch of homes go up in smoke and it is not a hundred year disaster. A creditable question is obviously how many one hundred year old trees live in your neighborhood. If none whatsoever, you may have a problem.

Pacific Northwest Research Station U.S. Forest Service

News & Information

USFS contact: David L. Peterson, (206) 732-7812,
USFS media assistance: Yasmeen Sands, (360) 753-7716,
UW contact: Jeremy Littell, (206) 221-2997,
UW media assistance: Sandra Hines, (206) 543-2580, shines@u.washington.edu

In the warming West, climate most significant factor in fanning wildfires’ flames

Study finds that climate’s influence on production, drying of fuels—not higher temperatures or longer fire seasons alone—critical determinant of Western wildfire burned area

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 Applications.

“We found that what matters most in accounting for large wildfires in the Western United States is how climate influences the build 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

Climate and wildfire area burned in western U.S. ecoprovinces, 1916–2003

Jeremy S. Littell
1,2,5, Donald McKenzie1,3, David L. Peterson3, and Anthony L. Westerling4,6

1Climate Impacts Group, Joint Institute for the Study of the Atmosphere and Ocean and Center for Science in the Earth System (JISAO/CSES), University of Washington, Box 355672, Seattle, Washington 98195-5672 USA

2Fire and Mountain Ecology Laboratory, College of Forest Resources, University of Washington, Box 352100, Seattle, Washington 98195-2100 USA

3USDA Forest Service, Pacific Northwest Research Station, 400 North 34th Street, Suite 201, Seattle, Washington 98103 USA

4Climate Research Division, Scripps Institution of Oceanography, University of California, San Diego, Mail Stop 0224, 9500 Gilman Drive, La Jolla, California 92093 USA

The purpose of this paper is to quantify climatic controls on the area burned by fire in different vegetation types in the western United States. We demonstrate that wildfire area burned (WFAB) in the American West was controlled by climate during the 20th century (1916–2003). Persistent ecosystem-specific correlations between climate and WFAB are grouped by vegetation type (ecoprovinces). Most mountainous ecoprovinces exhibit strong year-of-fire relationships with low precipitation, low Palmer drought severity index (PDSI), and high temperature. Grass- and shrub-dominated ecoprovinces had positive relationships with antecedent precipitation or PDSI. For 1977–2003, a few climate variables explain 33–87% (mean = 64%) of WFAB, indicating strong linkages between climate and area burned. For 1916–2003, the relationships are weaker, but climate explained 25–57% (mean = 39%) of the variability. The variance in WFAB is proportional to the mean squared for different data sets at different spatial scales. The importance of antecedent climate (summer drought in forested ecosystems and antecedent winter precipitation in shrub and grassland ecosystems) indicates that the mechanism behind the observed fire–climate relationships is climatic preconditioning of large areas of low fuel moisture via drying of existing fuels or fuel production and drying. The impacts of climate change on fire regimes will therefore vary with the relative energy or water limitations of ecosystems. Ecoprovinces proved a useful compromise between ecologically imprecise state-level and localized gridded fire data. The differences in climate–fire relationships among the ecoprovinces underscore the need to consider ecological context (vegetation, fuels, and seasonal climate) to identify specific climate drivers of WFAB. Despite the possible influence of fire suppression, exclusion, and fuel treatment, WFAB is still substantially controlled by climate. The implications for planning and management are that future WFAB and adaptation to climate change will likely depend on ecosystem-specific, seasonal variation in climate. In fuel-limited ecosystems, fuel treatments can probably mitigate fire vulnerability and increase resilience more readily than in climate-limited ecosystems, in which large severe fires under extreme weather conditions will continue to account for most area burned.

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