Archetypes of community wildfire exposure from national forests of the western US

Abstract

Risk management typologies and their resulting archetypes can structure the many social and biophysical drivers of community wildfire risk into a set number of strategies to build community resilience. Existing typologies omit key factors that determine the scale and mechanism by which exposure from large wildfires occur. These factors are particularly important for land managing agencies like the US Forest Service, which must weigh community wildfire exposure against other management priorities. We analyze community wildfire exposure from national forests by associating conditions that affect exposure in the areas where wildfires ignite to conditions where exposure likely occurs. Linking source and exposure areas defines the scale at which crossboundary exposure from large wildfires occurs and the scale at which mitigation actions need to be planned. We find that the vast majority of wildfire exposure from national forests is concentrated among a fraction of communities that are geographically clustered in discrete pockets. Among these communities, exposure varies primarily based on development patterns and vegetation gradients and secondarily based on social and ecological management constraints. We describe five community exposure archetypes along with their associated risk mitigation strategies. Only some archetypes have conditions that support hazardous fuels programs. Others have conditions where managing community exposure through vegetation management is unlikely to suffice. These archetypes reflect the diversity of development patterns, vegetation types, associated fuels, and management constraints that exist in the western US and provide a framework to guide public investments that improve management of wildfire risk within threatened communities and on the public lands that transmit fires to them.

Social vulnerability to large wildfires in the western USA

“…Homeowners, and not public land managers, are responsible for reducing the probability of home exposure to flames and burning embers by considering housing design, construction materials and maintenance of a home's immediate surrounding (defensible space) (Cohen, 2000), actions which may be more challenging in high social vulnerability communities. Although communities can be categorized into different biophysical fire exposure (Evers et al, 2019) or social archetypes , each community is different and its social vulnerability, as examined in this research, can indicate where we expect higher adaptive capacity and where both landscape and HIZ mitigation measures should be subsidized or funded by the government.…”

“…This study was replicated at three locations in the western US (North-central Washington; Central California; Northern New Mexico) that included large areas of federally administered lands (Fig. 1), and areas that have a high potential of fire transmission and exposure to neighboring communities based on evidence from recent studies (Ager et al, in review;Evers, Ager, Nielsen-Pincus, Palaiologou, & Bunzel, 2019;Scott et al, 2015;USDA Forest Service, 2018). In each study area, social vulnerability was related to wildfire exposure (expressed as the annual values of either structures affected or burned area), with exposure tied to the land tenure where it originated.…”

“…FSim incorporates modules for weather generation, wildfire occurrence, fire growth, and fire suppression, and is designed to simulate tens of thousands of hypothetical contemporary fire seasons (10,000 to 20,000 potential annual weather scenarios for the three study areas) (Finney et al, 2011;Short et al, 2016). Simulated perimeters were used to quantify the average annual area burned on each land tenure and the annual number of structures affected inside communities (Ager, Barros, & Day, 2015;Ager et al, 2014;Ager et al, 2017;Ager, Finney, & Vaillant, 2012;Ager, Palaiologou, Evers, Day, & Barros, 2018;Evers et al, 2019). Community boundaries were comprised by SILVIS WUI polygons (Radeloff et al, 2005; SILVIS Lab, 2012) that intersect the USA Census Bureau populated places layer (defined as community "cores") (Census, 2016), and all other SILVIS WUI layer polygons (SILVIS Lab, 2012) that fall within a 45-minute drive time distance from the core (Appendix C).…”

“…We intersected the combined land tenure and community layer with the block group boundaries. The derived layer was then intersected with the FSim fire perimeter layer (Evers et al, 2019). Intersections provided the parts of each fire perimeter that enter or escape the boundaries of each community, land tenure and block group.…”

Designing Operationally Relevant Daily Large Fire Containment Strategies Using Risk Assessment Results

“…Important variables to consider in pre-season, cross-boundary fire planning may also include ownership patterns, the extent and proximity of community and structures, the degree of pre-existing collaboration, and potential for conflict. Adopting thematic "archetypes" for community attributes [45] along with fire transmission and exposure pathways [46] could also prove useful for guiding and informing such planning efforts. Integrating those considerations into scenarios and using OR models to provide alternative containment suggestions would allow managers to understand the tradeoffs of different management policies and actions on various stakeholders.…”