Record-breaking fire weather in North America in 2021 was initiated by the Pacific northwest heat dome

Abstract

The 2021 North American wildfire season was marked by record breaking fire-conducive weather and widespread synchronous burning, extreme fire behaviour, smoke and evacuations. Relative to 1979–2021, the greatest number of temperature and vapor pressure deficit records were broken in 2021, and in July alone, 3.2 million hectares burned in Canada and the United States. These events were catalyzed by an intense heat dome that formed in late June over western North America that synchronized fire danger, challenging fire suppression efforts. Based on analysis of persistent positive anomalies of geopotential heights, the heat dome accounted for 21–34% of the total area burned in 2021. The event was 59% longer, 34% larger and had 6% higher maximum amplitude than the same event would have been without a warming climate. Climate change will continue to magnify heat dome events, increase fire danger, and enable extreme synchronous wildfire in forested areas of North America.