A 25-Year History of Spatial and Temporal Trends in Wildfire Activity in Oregon and Washington, U.S.A

We examined spatial and temporal trends in large fire incidents (> 400 ha) in Oregon and Washington. Our primary objectives were to examine whether patterns existed in the spatial and temporal distribution of large fires and to explore the relationship of patterns to climate variables using a geographic information system. We analyzed a historical fire database containing over 1000 fire incidents over a 25-year time period (1984 – 2008). We compared this fire database to climate variables representing historical estimates of average monthly maximum temperature, average monthly minimum temperate, average monthly dewpoint, and average monthly precipitation. Results showed an increasing trend in fire frequency, extent, magnitude, and fire season duration. Geospatial analytical techniques such as nearest neighbor analysis, quartic kernel density estimation, and quadrat analysis identified spatial patterning and hot spots of fire occurrence and size. The relationship of fire occurrence and size to climate variables was generally statistically indiscernible in our analysis results although some correlation was evident when fires were analyzed separately according to burn severity.