Weakened circulation yet stronger wildfires in Western North America

Western North America (WNA) has emerged as a global wildfire hotspot. While quasi-stationary atmospheric blocking drives persistent fire-favorable conditions, synoptic recurrent Rossby wave packets (RRWPs) represent a critical but underexplored driver of wildfire extremes. This gap is deepened by an apparent paradox that synoptic-scale circulation is projected to weaken under climate change while extreme wildfires intensify. Here we jointly analyze transient RRWPs and quasi-stationary blocking to classify extreme wildfire events in WNA. We then assess how these changing circulation patterns translate into fire risk using a novel wildfire-triggering efficiency framework powered by machine learning. Our results show that RRWPs contribute to wildfire extremes at magnitudes comparable to blocking, together explaining nearly two-thirds of events. Blocking shows only weak changes and RRWPs clearly weaken in WNA, but their wildfire-triggering efficiency is strongly enhanced by thermodynamic amplification. Under SSP5–8.5, blocking-related extreme wildfires increase by 45.9% and RRWP-related events by 37.1% by 2100. These findings establish a more complete picture of circulation controls on wildfires and identify thermodynamics as the primary driver of increasing wildfire risk in a warming future.