Contextualizing recent increases in Canadian boreal wildfire activity: decadal burn rates still within historical variability of the two past centuries

With approximately 15 million ha burned, the 2023 wildfire season in Canada was exceptional. However, it remains unclear whether such recent increases in burned areas exceed the range of variability observed over past centuries. The objective of this study was to leverage available dendrochronological reconstructions of decadal burn rates to contextualize their recent increase within their historical variability over the past two centuries. We compared decadal burn rate reconstructions based on dendrochronological data (1800-2023) for five large eastern and western Canadian boreal forest zones to those of recent decades up to 2023. The area burned in 2023 ranged from 0.76% to 32.5% among the five zones, which is unprecedented compared to the proportion recorded since 1972 for four of the five zones analyzed. In contrast, the burn rates of the decade ending in 2023 (i.e., 2014-2023) generally remained within the natural range of variability of the last two centuries. However, burn rates in two zones were close to the highest decadal burn rates observed since the 1800s and exceeded historical variability in one zone in western Canada. We discuss the historical and current trends in burn rates, their drivers and implications.