Shifting Wildfire Spread Dynamics in Canada

Wildfire activity in Canada has increased with climate change, but changes in how fires spread are less clear. Using the Canadian Fire Spread Dataset (2002–2024), this study shows that the number of days with active fire spread per fire more than doubled (+138%), driven by more frequent fire-conducive weather, leading to longer-lasting fires and higher potential spread. However, average daily spread distance declined sharply (−43.9%), and extreme spread events did not increase. The ratio of observed to potential spread also decreased, suggesting that landscape factors are increasingly limiting fire spread beyond climate effects. Two explanations are proposed: (1) increasing landscape resistance due to factors like fuel fragmentation, shifts to less flammable vegetation, and forest management; or (2) more severe fire weather allowing fires to enter previously resistant areas, giving the appearance of increased resistance. Despite regional differences, trends were consistent nationwide. Overall, more fire-conducive days are still driving larger fires and greater annual burned area. The results emphasize the importance of accounting for changing landscape resistance when predicting future wildfire activity under climate change.