Categorizing weather patterns associated with lightning-caused ignition clusters in Canada

Background Lightning-caused ignitions account for most annual area burned in Canada, and recent extreme fire seasons highlight the need to better understand atmospheric conditions that generate synchronous lightning-fire outbreaks. Aims We quantified lightning-caused ignition clusters (LCICs) across Canada from 1980–2023, examining their spatiotemporal characteristics and associated weather patterns in eastern and western Canada. Methods Using lightning-caused ignition records from the Canadian National Fire Database, we identified same-day LCICs with density-based spatial clustering. We computed anomalies in ERA5-derived synoptic variables and Canadian Forest Fire Danger Rating System (CFFDRS) fire weather indices on LCIC ignition dates and classified patterns using k-means clustering of 500-hPa geopotential height anomalies (Z500). Key results We identified 2407–2692 LCICs, representing 55–64% of lightning-caused ignitions. Composite analyses revealed predominantly positive Z500, 850-hPa temperature, and fire weather anomalies over LCIC centroids, with stronger anomalies in eastern Canada. Most LCICs occurred in the Boreal Shield, Montane Cordillera and Boreal Plains ecozones, with regional contrasts in LCIC size, area burned and seasonality. Conclusions LCICs are widespread and associated with distinct synoptic regimes and elevated fire weather severity, particularly in eastern Canada. Implications Our results provide additional information to support wildfire prediction, preparedness and proactive resource positioning.