Global fire size distribution: from power law to log-normal (original) (raw)
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Models, Data and Mechanisms: Quantifying Wildfire Regimes
… Society London Special …, 2006
The quantification of wildfire regimes, especially the relationship between the frequency with which events occur and their size, is of particular interest to both ecologists and wildfire managers. Recent studies in cellular automata (CA) and the fractal nature of the frequency-area relationship they produce has led some authors to ask whether the power-law frequency-area statistics seen in the CA might also be present in empirical wildfire data. Here, we outline the history of the debate regarding the statistical wildfire frequency-area models suggested by the CA and their confrontation with empirical data. In particular, the extent to which the utility of these approaches is dependent on being placed in the context of self-organized criticality (SOC) is examined. We also consider some of the other heavy-tailed statistical distributions used to describe these data. Taking a broadly ecological perspective we suggest that this debate needs to take more interest in the mechanisms underlying the observed power-law (or other) statistics. From this perspective, future studies utilizing the techniques associated with CA and statistical physics will be better able to contribute to the understanding of ecological processes and systems.
Wildfires are amajor 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. Lehsten, V., W. J. de Groot, M. Flannigan, C. George, P. Harmand, and H. Balzter (2014), Wildfires in boreal ecoregions: Evaluating the power law assumption and intra-annual and interannual variations, Journal of Geophysical Research - Biogeosciences, 119, 14–23. doi:10.1002/2012JG002252, http://hdl.handle.net/2381/28883
Wildfire Frequency-Area Statistics and their Ecological and Anthropogenic Drivers
2003
Frequency-area statistics of wildfire regimes in USA and British Columbia, Canada, are examined and suggested to exhibit power-law behaviour across many orders of magnitude. Two parameters are used to compare regimes for anthropogenic and ecological drivers of this behaviour. The frequencies of fires (log alpha) and ratios of large to small fires (beta) are greater for: USA National Parks (NPs) compared to their surrounding areas; Washington state NPs compared to British Columbia NPs; and human-caused fires compared to lightning-caused fires. Recent work on the self-organization and thermodynamics of open systems is presented and related to wildfire occurrence in ecosystems of the USA.
Scaling and correlations in the dynamics of forest-fire occurrence
Physical Review E, 2008
Forest-fire waiting times, defined as the time between successive events above a certain size in a given region, are calculated for Italy. The probability densities of the waiting times are found to verify a scaling law, despite that fact that the distribution of fire sizes is not a power law. The meaning of such behavior in terms of the possible self-similarity of the process in a nonstationary system is discussed. We find that the scaling law arises as a consequence of the stationarity of fire sizes and the existence of a non-trivial ``instantaneous'' scaling law, sustained by the correlations of the process.