Large wildfires generally travel along a trajectories set by the local wind direction. For example, persistent southeast winds during May 2023 in Alberta resulted in multiple large fires with the exact same elliptical shape oriented from the southeast to the northwest. 

Alberta wildfire polygons May 6, 2023 (Screenshot from Alberta Wildfire Status Dashboard)

Despite the highly directional nature of wildfire spread, most assessments of fire risk are omnidirectional, meaning the risk level assessed at a given location exists for every direction. In this study, we tried something different. Our goal was to describe the directional pattern of wildfire hazard around a community.

Communities are surrounded by a patchwork of different landcovers, such as water (lakes, rivers), grasslands, and forests. Some land covers are more flammable than others, and their directional positions around a community vary.

For example, the hamlet of Marten Beach, Alberta, sits on the north shore of Lesser Slave Lake. Due to the orientation of the large lake in relation to the community, a fire spreading from the southwest has no potential to reach this community. Directional vulnerabilities are not always so obvious.

Source: Google Earth (Landsat/Copernicus)

There can be a complex mix of different cover types with different sizes and shapes distributed across an area. ​In Alberta’s fire-prone ecosystems,  conifer fuels like white spruce, black spruce, and lodgepole pine pose the greatest threat to the built environment. That's because they support high intensity fires and generate abundant ember showers that can rain down on nearby structures. Exposure of structures to these potential ignition sources can be easily measured (i.e., Beverly et al. 2010) and patterns of exposure across landscapes can be mapped using these same methods (Beverly et al. 2021).

In this study,  we took the landscape exposure patterns mapped by Beverly et al. (2021) for Alberta, and developed a standard way to describe the directional pattern of high exposure areas in relation to a locale of interest. The results are easy to interpret and show the potential for fire encroachment for all possible directions around a community. Below you can see the directinoal vulnerabilities we mapped for two communities in Alberta: Rainbow Lake (left) and Edson (right).​ In the case of Edson, you can see that when a fire burned towards the community from the southeast in June 2023 (shown in gray shading), it approached the community along one of the viable pathways we had mapped.

Viable fire pathways into the community of Rainbow Lake, Alberta. Imagery source: Google Earth (Landsat/Copernicus)

Viable fire pathways into the community of Edson, Alberta and 2023 wildfire (gray shading). Imagery source: Google Earth (Landsat/Copernicus)