Mid-21st century shifts in fire regimes of PNW westside forests due to future climate change and impacts to communities
Webinar registration.
Presenters: John Kim, USDA Forest Service
Alex Dye, Oregon State University
Description: Fire is an integral part of the disturbance regime of the Pacific Northwest’s moist temperate forests, but future fire patterns for this region remain uncertain. Using Energy Release Component (ERC) from 12 global climate models (GCM), we simulated thousands of plausible fire seasons with the fire spread model FSim for mid-21st century (2035-2064) for 5 northwestern pyromes. Projected changes to burn probability, fire size, and number of fires varied among pyromes and GCMs. The largest increases in burn probability and fire size occur in the cooler and wetter northern parts of the region (North Cascades, Olympics & Puget Lowlands) and Oregon West Cascades, with more moderate changes projected for the Washington West Cascades and Oregon Coast Range. We provide new insights into changing fire regimes characterized by the possibility of shifts towards more frequent large fires (especially > 40,000 ha), and shifts in seasonality, including more fires burning at the beginning of fall when extreme synoptic weather events have the potential to increase fire spread and fire’s impact on communities. Our work highlights the potential geographic variability in climate change effects in the Northwest, pointing to a rapid acceleration of fire in the coming decades for which current wildfire risk reduction strategies based on recent historical data, and not climate change or rare events, may be insufficient.
Risk assessments that account for climate change and rare events can help prepare expectations for how future changes to fire regimes will impact communities, and we explore these impacts using two different methods for the present and future time periods. We used building location data to evaluate community wildfire exposure and identify plausible disasters that are not based on mean-based statistical approaches. Nearly half of communities are vulnerable to a future disaster, and the magnitude of plausible disasters exceeds any recent historical events. Ignitions on private land are most likely to result in very high community exposure. We also conducted a screening of wildfire evacuation vulnerability for 696 Oregon and Washington rural towns. By combining the road and fire metrics, we score and rank all towns by their overall evacuation vulnerability. Many of the most vulnerable towns are located in remote, forested, mountainous terrain, where topographic relief constrains the available road network and high fuel loads increase wildfire hazard. Work is underway to characterize how the vulnerabilities shift by mid-century.