Portland State University. Department of Environmental Science and Management
Term of Graduation
Date of Publication
Master of Science (M.S.) in Environmental Science and Management
Environmental Science and Management
Wildfire risk -- Oregon -- Clackamas River Watershed, Climatic changes -- West (U.S.), Wildfire forecasting -- Oregon -- Clackamas River Watershed, Wildfire risk -- Oregon -- Clackamas River Watershed -- Management
1 online resource (viii, 106 pages)
In the western United States, climate change is projected to lead to significant changes in regional wildfire regimes. Historically, forests west of the Cascade crest in Oregon and Washington, USA (westside) have been characterized by low-frequency wildfire events, but climate change projections indicate that wildfire could become a more common disturbance, altering ecological processes and impairing ecosystem services like surface water quality and quantity. Wildfire risk assessments based on simulation models have been used in high frequency fire regimes to evaluate contemporary and future risk, but present unique challenges in westside forests because characteristic low annual burn probabilities result in determinations of low risk. In this thesis, I evaluated wildfire hazard in the Clackamas River watershed (Clackamas), a municipal watershed in western Oregon, under contemporary and projected mid-century climate conditions using the large fire simulator, FSim. In Chapter One, I modeled four climate scenarios from the Coupled Model Intercomparison Project (CMIP5) under RCP 8.5. Results demonstrated that climate change will likely lead to significant changes in fire size, frequency, and fire season length, but a wide range of future conditions is possible. In Chapter Two, I explored the challenges to communicating risk from low probability, high consequence events and presented a framework for evaluating the impact of climate change on surprising, impactful wildfires. Results demonstrated the plausibility of surprising wildfires under contemporary conditions, and showed that surprising wildfires will be increasingly plausible under hotter and drier conditions. The modeled changes in westside fire regimes indicate that historic and contemporary fire regime characteristics are not a complete guide for future disturbance regimes. The combination of probabilistic and surprise fire analysis demonstrated the need for robust risk mitigation and adaptation strategies in the face of a range of plausible futures.
© 2020 Andy McEvoy
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McEvoy, Andy, "Wildfire Risk Assessment for a Municipal Watershed in Western Oregon, USA: Methods for Projecting the Impact of Mid-21st Century Climate Change on Wildfire Hazard" (2020). Dissertations and Theses. Paper 5631.