Climate and Wildfire in the Western United States
نویسنده
چکیده
MAY 2003 AMERICAN METEOROLOGICAL SOCIETY | T he number and extent of wildfires in the western United States each season are driven by natural factors such as fuel availability, temperature, precipitation, wind, humidity, and the location of lightning strikes, as well as anthropogenic factors. It is well known that climate fluctuations significantly affect these natural factors, and thus the severity of the western wildfire season, at a variety of temporal and spatial scales. Previous studies (Simard et al. 1985; Swetnam and Betancourt 1990; Jones et al. 1999) have demonstrated that large-scale climate patterns in conjunction with El Niño affect the frequency and extent of wildfires that occur in particular regions of the United States. Swetnam and Betancourt (1998) and Balling et al. (1992) have found relationships between the Palmer Drought Severity Index (PDSI) and fire season severity. Our study differs from earlier work in its resolution, comprehensiveness, and regional scale. Until now, the lack of a comprehensive fire climatology has hampered detailed studies of climate–fire relationships. Some previous studies (e.g., Simard et al. 1985; Swetnam and Betancourt 1998; Mote et al. 1999) have looked at wildfires by state or larger regions, aggregating fire statistics for many different fuel types and climates, with the result that relationships between climate, fuel type, and fire severity may be obscured. Others have focused on climate influences upon wildfires aggregated at the level of the forest or stand (e.g., Swetnam and Betancourt 1998; Balling et al. 1992)—a finer resolution than pursued here— for smaller regions. Our study is the first to consider the larger picture of wildfire for the entire western United States, including fire histories from several federal agencies whose territories span a diverse array of ecosystems. The quality of the location data for some of these fire histories constrains a comprehensive, regional-scale analysis to a 1° grid resolution. This level of aggregation obscures some of the rich detail of wildfire variability related to the enormous variability in vegetation within the western United States. However, at the same time it provides a common fire history with comprehensive coverage over CLIMATE AND WILDFIRE IN THE WESTERN UNITED STATES
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