International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire

Fire weather index system components for large fires in the Canadian boreal forest

B. D. Amiro A D , K. A. Logan B , B. M. Wotton B C , M. D. Flannigan B , J. B. Todd A , B. J. Stocks B and D. L. Martell C
+ Author Affliations
- Author Affliations

A Canadian Forest Service, Northern Forestry Centre, 5320-122 Street, Edmonton, AB, T6H 3S5, Canada.

B Canadian Forest Service, Great Lakes Forestry Centre, 1219 Queen Street East, Sault Ste. Marie, ON, P6A 2E5, Canada.

C Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, ON, M5S 3B3, Canada.

D Corresponding author. Present address: Department of Soil Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada. Telephone: +1 204 474 9155; email:

International Journal of Wildland Fire 13(4) 391-400
Submitted: 16 September 2003  Accepted: 27 July 2004   Published: 15 December 2004


Canadian Fire Weather Index (FWI) System components and head fire intensities were calculated for fires greater than 2 km2 in size for the boreal and taiga ecozones of Canada from 1959 to 1999. The highest noon-hour values were analysed that occurred during the first 21 days of each of 9333 fires. Depending on ecozone, the means of the FWI System parameters ranged from: fine fuel moisture code (FFMC), 90 to 92 (82 to 96 for individual fires); duff moisture code (DMC), 38 to 78 (10 to 140 for individual fires); drought code (DC), 210 to 372 (50 to 600 for individual fires); and fire weather index, 20 to 33 (5 to 60 for individual fires). Fine fuel moisture code decreased, DMC had a mid-season peak, and DC increased through the fire season. Mean head fire intensities ranged from 10 to 28 MW m-1 in the boreal spruce fuel type, showing that most large fires exhibit crown fire behaviour. Intensities of individual fires can exceed 60 MW m-1. Most FWI System parameters did not show trends over the 41-year period because of large inter-annual variability. A changing climate is expected to create future weather conditions more conducive to fire throughout much of Canada but clear changes have not yet occurred.

Additional keywords: drought; duff moisture; fire intensity; forest fire; seasonality; taiga; trends.


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