Disentangling the roles of natural variability and climate change in Canada’s 2023 fire season

Canada’s 2023 wildfire season was the most extreme on record, with almost 15 million hectares burned—more than double the previous record. We use an established attribution protocol to examine seasonal and regional changes in weather-related wildfire risk associated with global warming, and also evaluate the extent to which 2023’s unusual level of blocking activity contributed to the severity of the season. We find that the annual accumulated daily severity rating (DSR), a measure of weather-related fire risk) is increasing in most ecozones in response to global warming, with the largest increases in the early months of the fire season; although temperatures are increasing everywhere, this effect is offset in some regions by increased precipitation. Blocking circulation patterns are likewise associated with increased DSR, with the strongest responses in May and September. However, there is wide regional variability, illustrated through two case studies of regions that experienced particularly intense wildfires. In the southern Taiga Plains, the contribution from anthropogenic climate change is unclear, while blocking activity increased the severity of the season by at least 33%; in the East James Bay region, the season was found to be at least 32% more intense due to global warming, and a further 15% more intense due to blocking activity.