Monday, 17 November 2003
The weather of large fires in the Canadian boreal forest
The weather experienced during large fires (> 200 ha in area) was analyzed for Canada from 1959 to 1999. Maximum values of Canadian Fire Weather Index parameters were calculated using interpolated daily weather data for each fire. Depending on ecozone, the means of parameters ranged from: Fine Fuel Moisture Code 90 to 92 (85 to 97 for individual fires), Duff Moisture Code 44 to 78 (10 to 140 for individual fires), and Duff Moisture Code 210 to 372 (50 to 700 for individual fires). Mean head fire intensities ranged from 14 to 28 MW/m in the boreal spruce fuel type, and were about 3.5 MW/m in the spruce-lichen woodland fuel type. Frequency distributions of these parameters for each ecozone show a wider range. There has been a significant increase in the number of large fires and area burned for all Canada and for several ecozones. There is some uncertainty because of potential missing fires in the early years, but the trend is likely real, dominated by 7 large fire years since 1980. Fire weather indices did not show consistent trends, except for the number of fire days above certain thresholds in the Taiga Shield ecozones and for all Canada. This may be confounded by fires missed in the early years. A changing climate is expected to create weather conditions more conducive to fire through much of Canada. Our dataset shows a weak signal over a 41-year period, and further monitoring will determine whether climate change is having an effect on fire in Canada.