Pyrogeography of the Southeast USA: Exploring the Relationships between Wildfire and Climate
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Wildfire plays a contradictory role as both a hazard and a necessary ecological process in certain ecosystems. A variety of factors influence wildfire, including fuel type and quantity, land management policies, and patterns of human activity. Climate, however, can often play a dominant role. Wildfires are often thought to occur only in the western United States; however, fires are common on the southeastern U.S. landscape. Despite the abundance of fires, limited fire climatology work has been performed in this region. This dissertation addresses a knowledge gap in Southeast fire climatology by examining how gradients in precipitation regimes, in particular precipitation variability, influence spatial patterns of wildfire. In addition, modern synoptic climatology techniques are used to examine the relationships between atmospheric circulation patterns and wildfire ignitions in the central Gulf Coast sub-region of the Southeast. Chapter II characterizes precipitation regimes in Southeast national forests and associates mean annual ignition density and mean annual area burned with various precipitation metrics. Weak positive correlations were observed between daily precipitation variability and mean annual ignition density. Chapter III employs the Spatial Synoptic Classification (SSC) scheme to examine weather types associated with wildfire ignitions in the central Gulf Coast. Results show that dry tropical (DT) days occurred more often during years with higher numbers of ignitions in central Gulf Coast national forests, as well as in the 180, 90, and 30-day periods prior to a fire. DT weather types occurred most commonly in the fall and spring corresponding with peak fire seasons in much of the region. Particularly in the spring, DT variability was influenced by positive phases of the North Atlantic Oscillation (NAO), presumably increasing westerly flow and driving DT weather types farther east from their general source region. Finally, chapter IV developed eleven synoptic types using the Synoptic Typer Tool (STT). Principal Component Analysis (PCA) was applied to daily (18z) 500 mb geopotential height grids. Synoptic types were then linked with wildfire ignitions in the central Gulf Coast. Results suggested that troughs were associated with wildfire activity, as well as zonal flow and high pressure systems.