Geospatial Fire History of California

Fire in California has a history well beyond that of humans in the landscape. However, with the arrival of humans, the ecological process of fire has been altered substantially. Beginning with Native Americans’ use of fire as a tool for managing the landscape, and then the highly aggressive attack on fire by European settlers, fire in California has changed. In the past decade we have begun to see these changes—larger and more intense wildfires are becoming a frequent and expected phenomenon. This study was designed to provide a contextual basis for understanding changes to wildfire geographies (pyrogeography) in California from 1900 through 2011. With this framework, future studies can be placed within the evolving pyrogeography.

This study directly investigates how wildfires have spatially changed in California over the past century. Specifically:

  • Has the number and size of wildfires increased over the past century?
  • Has the geometry of wildfire boundaries changed over the past century?
  • Are wildfires starting to burn in new types of vegetation?
  • Have specific ecological regions experienced more substantial increases in wildfire activity than others?
  • Has the spatial distribution of wildfires in California moved over the past century?
    1. How has the mean center of wildfires moved?
    2. Are there specific clusters of wildfires in California, and have those clusters moved over the past century?

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Geospatial analyses are the primary tool used in this study. Analyses were conducted across the temporal scale of the last century and the spatial scale of major ecological regions of California. Initial exploratory data analysis (EDA) provides insight to the data—its weaknesses and strengths, its distribution and general trends. Upon initial exploration of the data, some pattern analysis is conducted to assess the level of global spatial distribution—with and without correlations with the primary value of focus (fire size). After analyzing the global patterns, local clusters of fires are identified by measuring the spatial autocorrelation of fire size—special attention given to large fires (greater than 1,000 hectares). Lastly, interpolated surfaces were created with kriging methods. These surfaces predict the average fire size throughout California, and can be used to identify areas most susceptible to large fires. They can also be qualitatively compared to the clusters identified by spatial autocorrelation methods.

As a whole, this study provides a quantitative historical context upon which the current situation of fire can be placed. While many studies have been conducted on a larger, more local scale, there have been very limited analyses at this scale and with these techniques. This study illuminates the changing spatiotemporal role of fire in California.

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