Canadian Forest Service Publications
Wildfires in boreal ecoregions: evaluating the power law assumption and intra-annual and interannual variations. 2014. Lehsten, V.; de Groot, W.J.; Flannigan, M.; George, C.; Harmand, P.; Balzter, H. Journal of Geophysical Research: Biogeosciences 119:14-23.
Issued by: Great Lakes Forestry Centre
Catalog ID: 35495
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Wildfires are a major driver of ecosystem development and contributor to carbon emissions in boreal forests. We analyzed the contribution of fires of different fire size classes to the total burned area and suggest a novel fire characteristic, the characteristic fire size, i.e., the fire size class with the highest contribution to the burned area, its relation to bioclimatic conditions, and intra-annual and interannual variation. We used the Canadian National Fire Database (using data from 1960 to 2010) and a novel satellite-based burned area data set (2001 to 2011). We found that the fire size distribution is best explained by a normal distribution in log space in contrast to the power law-based linear fire area relationship which has prevailed in the literature so far. We attribute the difference to previous studies in the scale invariance mainly to the large extent of the investigated ecoregion as well as to unequal binning or limiting the range at which the relationship is analyzed; in this way we also question the generality of the scale invariance for ecoregions even outside the boreal domain. The characteristic fire sizes and the burned area show a weak correlation, indicating different mechanisms behind each feature. Fire sizes are found to depend markedly on the ecoregion and have increased over the last five decades for Canada in total, being most pronounced in the early season. In the late season fire size and area decreased, indicating an earlier start of the fire season.
Plain Language Summary
Firefighting and evacuation activities are based on the assessment of expected number, intensity, and sizes of fires, which affects fire management strategy and decision making. This makes the distribution of fire sizes of economic interest. In this study we developed a novel statistic: the characteristic fire size, which indicates the size of fire that typically contributes the highest proportion to the total burned area in an ecoregion. We analyzed 50 years of fire data for the boreal biome from the Canadian National Fire Database. We found that the characteristic fire size as well as the annual burned area has increased over the last five decades in Canada. Both have the strongest increase early in the season, while the late season shows a decreasing trend. Typical fire size will be useful for other planning actions such as initiating natural fire regimes.