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, readily-available metric of landscape fire exposure to develop a systematic, standardized, descriptive assessment of directional vulnerability to wildfire at a point location. 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 less than 1/5th of its length traversing low exposure. Using this criterion, we assessed the viability of directional trajectories around 913 small- to moderately-sized communities in the province. At each assessment point (i.e., community centroid), we delineated 360 possible wildfire trajectories into the community at 1° directional intervals. Each 15 km directional trajectory was divided into three equal-length segments for analysis, spanning: 0 (centroid) to 5 km; 5 km to 10 km; and 10 km to 15 km. The length of each directional trajectory segment that intersected high exposure was computed for all 1080 directional segments in each community study area. In total, we evaluated 986,040 directional segments. Communities exhibited highly unique and varied patterns of directional vulnerabilities to wildfire encroachment. Of the 913 communities analyzed, 136 had at least one continuous viable trajectory spanning the full 0-15 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 a novel radial graph 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 wildfire assessment method are discussed, including prioritization of limited fire suppression resources, planning fuel reduction treatments, proactively identifying candidate locations for operational activities, and assessing evacuation vulnerabilities.

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.…”