Characterizing extreme fire and weather events in the Boreal Shield ecozone of Ontario

Abstract

Fire frequency is the most commonly used measure to characterize fire regimes for comparisons across geographical areas or time periods. Within the boreal forest region of the Boreal Shield ecozone of Ontario, fire frequency changes over time and across longitudinal gradients have been associated with drought frequency and large-scale climate processes. While providing evidence that fire regimes differ across areas of the Boreal Shield, fire frequency alone provides little insight into the potential for extreme fire events and the extreme fire weather events that produce large and intense fires characteristic of boreal forest ecosystems. We used the statistics of extreme values to characterize dry spell extremes, or runs of consecutive days with little or no rain, and fire size extremes in east (BSE) and west (BSW) divisions of the Boreal Shield ecozone of Ontario. Extreme fire-event distributions over the 1976–1999 period were compared between two sites in the boreal forest region (i.e., Northern Coniferous and Northern Clay) and extreme dry spell event distributions for the 1963–1998 period were compared between two weather stations (i.e., Dryden and Kapuskasing). Distributions of extreme fire and dry spell events in the BSW and BSE were significantly different. Return time of a 10 000 ha fire was 5.2 years in BSW and 91.8 years BSE. Differences in dry spell extremes were consistent with fire extremes, with the return time of a 30 day dry spell event increasing from 7.5 years in the BSW to 27.8 years in the BSE.