Spatiotemporal analysis of Holocene fire regimes between US Northwest and Southwest regions

Authors: Katherine Beall*, , Julie Loisel, Department of Geography, Texas A&M University
Topics: Physical Geography, Paleoenvironmental Change
Keywords: fire, charcoal, Western United States, Holocene
Session Type: Poster
Day: 4/11/2018
Start / End Time: 8:00 AM / 9:40 AM
Room: Napoleon Foyer/Common St. Corridor, Sheraton, 3rd Floor
Presentation File: No File Uploaded

The western United States frequently experiences wildfires, which have important consequences on our societies and the natural environment. To understand the key controls on fire frequency, severity, and intensity, charcoal data that span the Holocene have been compiled in the Global Charcoal Database (GCD) for analysis of past relationships between fire and environmental conditions. However, most analyses view the western United States as a single ‘fire unit’ despite clear climatic differences between the Northwest and the Southwest. Dividing the western United States into these two regions prior to charcoal data analysis addresses this issue. Here, composite fire trends were reconstructed from the GCD charcoal data to represent the occurrence of fires throughout the Holocene. In addition, the gridded Palmer Drought Severity Index (PDSI) database from the past 2,000 years was used to evaluate differences in drought conditions between our two study regions. We found that, while the Northwest experienced an increase in fires throughout the past 15,000 years, the Southwest experienced a more stable occurrence of fires (i.e., no upward or downward trend over time), though it was also characterized by a greater variability around the mean. PDSI analysis showed a distinct difference in drought conditions between the Northwest versus the Southwest. Though additional statistical methods are desired to confirm our findings, we show that the Northwest and Southwest regions should be viewed as two separate ‘fire units.’

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