Enhanced prediction of extreme fire weather conditions in spring using the Hot-Dry-Windy Index in Alberta, Canada

Abstract

Fire weather indices used to forecast fire behaviour provide valuable information for wildland fire prevention, preparedness, and suppression. The primary index used in Canada, the Fire Weather Index System, provides qualitative fuel moisture and fire behaviour indices. However, the indices used to predict and forecast fuel moisture and fire behaviour do not assess the impacts of weather alone. Weather strongly influences fuel moisture, fire ignition, and fire spread. Additionally, the spring fire season in Alberta, Canada has been challenging for decades. Alberta has historically experienced extreme fire weather conditions in the spring season, leading to the occurrence of multiple disastrous wildland fires. This study examines the association between the Hot-Dry-Windy Index (HDWI) and spread days on 80 large wildland fires greater than 1,000 hectares that started in the month of May in Alberta from 1990 to 2019. HDWI values were calculated using ERA5 reanalysis weather from the 1000, 975 and 950 hPa levels. Permutation tests were used to test HDWI distributions between spread days and non-spread days. Statistically significant differences between HDWI values were found between the distributions of spread days and non-spread days over the first four days of all 80 large wildland fires in the dataset, as well as on the day of assessment of these fires. Results of this study suggest that HDWI can contribute to the prediction of significant spring wildland fire spread days in Alberta’s fire prone landscapes. A climatology of May HDWI values from 1990 to 2020 was also created for three separate locations in Alberta to provide context to HDWI values.