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

Authors

  • Jeremy S. Littell,

    Corresponding author
    1. Climate 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
    2. Fire and Mountain Ecology Laboratory, College of Forest Resources, University of Washington, Box 352100, Seattle, Washington 98195-2100 USA
    Search for more papers by this author
  • Donald McKenzie,

    1. Climate 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
    2. USDA Forest Service, Pacific Northwest Research Station, 400 North 34th Street, Suite 201, Seattle, Washington 98103 USA
    Search for more papers by this author
  • David L. Peterson,

    1. USDA Forest Service, Pacific Northwest Research Station, 400 North 34th Street, Suite 201, Seattle, Washington 98103 USA
    Search for more papers by this author
  • Anthony L. Westerling

    1. Climate Research Division, Scripps Institution of Oceanography, University of California, San Diego, Mail Stop 0224, 9500 Gilman Drive, La Jolla, California 92093 USA
    Search for more papers by this author
    • 6 Present address: School of Engineering and School of Social Sciences, Humanities, and Arts, University of California, Merced, California 95344 USA.


  • Corresponding Editor: M. Friedl.

Abstract

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.

Ancillary