On October 1, 2018, Raphael Chavardes presented, "Fire Synchrony and its Climatic Drivers in the Southern Cordillera of Western Canada" at the University of Alberta.
During each of the last four fire seasons (2015–2018), large, high-severity forest fires burned at multiple locations in western Canada causing the evacuation of thousands of people from local communities. These recent fires occurred during dry climate conditions over the fire season although spatial and temporal patterns of drying varied. If these fires were only associated with 20th–21st century changes in climate, then we would expect to find less evidence of fires burning at multiple locations in the historical records. To investigate this, we used multi-century fire-scar records from the southern cordillera of western Canada. Fire-scar records composed of 1,886 samples from 17 fire-history sites across the region revealed that fires burning at multiple sites (over 20% of sites) were historically common between 1746 and 1945, a 200 year interval preceding advanced and organized fire suppression capabilities. By using multi-century tree-ring reconstructions of drought, precipitation, and maximum temperature, we found fires burning at multiple sites and two-four subregions of the southern cordillera were associated with drier and warmer climate conditions. To explore the historical spatial and temporal associations between fire and climate across subregions, we used spatial interpolation with networks of drought and precipitation reconstructions. We found spatially focalized low precipitation leading up to the fire season was an important factor in driving historical fires although summer drought was also a common driver. Our findings reveal that climate was a strong driver of historical fires; however, given that fire-scar records provide evidence of low-severity fires, these types of records contrast with many of the most recent 21st C. high-severity fires which burned in the southern cordillera. Apart from changes in climate, a likely contributing factor which may have led to this change in fire behavior is the increase of ground and ladder fuels found in many locations of western North America following the implementation of fire exclusion policies and the development of fire suppression over the 20th C.