Assessing directional vulnerability to wildfire

Abstract

Wildfires spread along trajectories set by a coincident wind direction. Despite the highly directional nature of wildfire threats to public safety, landscape fire risk assessments are typically omnidirectional. We used a simple metric of landscape fire exposure to develop a systematic and standardized approach for assessing directional vulnerability to wildfire within a circular assessment area centered on locale of interest. First, we defined a viable wildfire trajectory by analyzing 573 sample trajectories delineated within the burned areas of historical fires in the province of Alberta, Canada. On average, sample trajectories intersected locations assessed as having high wildfire exposure for 79% of their length. We, therefore, defined a viable fire trajectory as one with at least 80% of its length traversing high exposure. Using this criterion, we assessed the viability of directional trajectories representing possible wildfire pathways from outlying landscape areas into a locale of interest centered within a roughly 70,000-ha circular assessment area. At each central assessment point (i.e., community centroid), we delineated 360 linear trajectories into the community at 1° directional intervals. Each 15-km trajectory was divided into three 5-km segments for analysis (inner, middle, and outer). The length of each directional trajectory segment that intersected high exposure was computed for all 1080 directional segments in each community assessment area. In total, we evaluated 986,040 directional segments for 913 communities in the province. Communities exhibited highly unique and varied patterns of directional vulnerabilities to wildfire encroachment. Of the communities analyzed, 136 had at least one continuous viable trajectory spanning the full 15-km distance from the community centroid, and 211 communities had at least one continuous viable trajectory spanning 5–15 km from the community centroid. We developed customized rose or polar diagrams for displaying spatially referenced directional vulnerabilities to wildfire for a given community and combined results for all 913 analyzed communities to assess regional vulnerabilities within administrative management areas (i.e., Forest Areas). Potential applications of our directional assessment method are discussed, including prepositioning and prioritizing limited fire suppression resources, planning fuel reduction treatments, proactively identifying candidate locations for operational activities, assessing transportation network vulnerabilities during evacuations, and scenario planning.

Mapping the distance between fire hazard and disaster for communities in Canadian forests

“…Communities with strong directional trends in simulation reflect trends of fire-conducive environmental factors, especially fire weather conditions (e.g. wind direction), fuel distribution (Beverly & Forbes, 2023) and ignition patterns. On the other hand, topography potentially modifies the spatial trends of these factors, which may weaken the directional trends for some communities while strengthening them for others.…”

“…wind direction). Similarity between the two implies that fuel distribution is the predominant factor in shaping fireshed pathways and corridors (see also Beverly & Forbes, 2023).…”

“…While fuel connection is crucial to provide a pathway for wildland fire to spread to a community (e.g. Beverly & Forbes, 2023), fire spread distance and direction are also influenced by weather and topography. In this study, we investigate how fire spread rates and fire perimeters generated from fire simulation models can be used to map firesheds, fire pathways and spread distances.…”

An efficient, multi-scale neighbourhood index to quantify wildfire likelihood

“…For example, Beverly et al (2021) make use of the empirical evidence that highly 'local' features influence wildfire likelihood and subsequent building losses (Caggiano et al 2020). They present a model that spatially aggregates the presence or absence of hazardous fuels within a predefined radius of an asset (for example, within 500 m) and provide a novel methodology for examining the directionally specific landscape arrangement of these hazardous fuels relative to a point of interest (Beverly and Forbes 2023). Alternatively, Verde and Zêzere (2010) combine several chosen weather, fuel and topography factors in a multiplicative fashion to provide a measure of wildfire likelihood, and Liberatore et al (2021) use the connectivity of treatable fuel polygons as a surrogate for wildfire likelihood.…”