Atmospheric and oceanic drivers behind the 2023 Canadian wildfires

In the 2023 summer, wildfires in Canada were exceptionally intense, producing the highest carbon emissions recorded since 2003 and affecting much of North America. However, the factors driving the 2023 wildfires and their interactions remain poorly understood. Here we demonstrate that the 2023 Canadian wildfires were primarily fueled by persistent, intense and widespread summer surface warming, along with pronounced reductions in precipitation and soil moisture. These conditions were closely linked to unusually frequent, wide, long-lasting and eastward-moving North American blocking events. We reveal that an unusually strong negative Pacific Decadal Oscillation and an Eastern Pacific El Niño in the 2023 summer play a crucial role in promoting these blocking patterns. Furthermore, we find that abnormally low precipitation and soil moisture during the preceding winter and spring served as critical precursors, compounding summer fire risk by preconditioning the landscape. Our findings offer new insights into the underlying causes of the 2023 Canadian wildfires. The unprecedented intensity of the 2023 Canadian wildfires was primarily driven by persistent summer warming, reduced precipitation and soil moisture due to increased persistence and frequency of North American blocking events linked to oceanic anomalies, according to an analysis of climate data, ocean-atmosphere interactions, and seasonal hydrological conditions.