Overwintering fires rising in eastern Siberia

Overwintering fires are a historically rare phenomenon but may become more prevalent in the warming boreal region. Overwintering fires have been studied to a limited extent in boreal North America; however, their role and contribution to fire regimes in Siberia are still largely unknown. Here, for the first time, we quantified the proportion of overwintering fires and their burned areas in Yakutia, eastern Siberia, using fire, lightning, and infrastructure data. Our results demonstrate that overwintering fires contributed to 3.2 +/- 0.6% of the total burned area during 2012-2020 over Yakutia, compared to 31.4 +/- 6.8% from lightning ignitions and 51.0 +/- 6.9% from anthropogenic ignitions (14.4% of the burned area had unknown cause), but they accounted for 7.5 +/- 0.7% of the burned area in the extreme fire season of 2020. In addition, overwintering fires have different spatiotemporal characteristics than lightning and anthropogenic fires, suggesting that overwintering fires need to be incorporated into fire models as a separate fire category when modelling future boreal fire regimes.