When is fire weather extreme enough for active fire spread in Canada?

A spread day is defined as a day in which fires grow by a substantial amount of area, usually during high or extreme fire weather conditions. Accurately identifying a spread day under various environmental conditions could help both our understanding of fire regimes and with forecasting and managing fires on the ground. Although spread days could occur within a spectrum of fire weather conditions, a threshold is important to fire management and fire research. This study explores the relationships between spread days and fire activity in the forested area of Canada by spatially and temporally matching daily fire growth to interpolated daily gridded fire weather between 2001 and 2021. Using accumulative area burned density functions, we identified the fire weather conditions for spread days by Canadian Ecozones both annually and seasonally. Using these identifiers as thresholds, we estimated how extreme fire weather needs to be for a spread day to occur, and the proportions of potential spread days (PSDs) that would most likely be realized in real fire spread at various Canadian Ecozones. Our results showed that the median-level fire-conducive weather conditions are sufficient to support active fire growth, and on average, about 22-30% of such days may be realized in real fire spread at various Canadian Ecozones.This article is part of the theme issue 'Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks'.