NPG Nonlinear Processes in Geophysics NPG Nonlin. Processes Geophys. 1607-7946 Copernicus Publications Göttingen, Germany 10.5194/npg-18-381-2011 A semi-phenomenological approach to explain the event-size distribution of the Drossel-Schwabl forest-fire model Hergarten S. 1 Krenn R. 1 Institut für Erdwissenschaften, Karl-Franzens-Universität Graz, Heinrichstraße 26, 8010 Graz, Austria 21 06 2011 18 3 381 388 Copyright: © 2011 S. Hergarten 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://npg.copernicus.org/articles/18/381/2011/npg-18-381-2011.html The full text article is available as a PDF file from https://npg.copernicus.org/articles/18/381/2011/npg-18-381-2011.pdf

We present a novel approach to explain the complex scaling behavior of the Drossel-Schwabl forest-fire model in two dimensions. Clusters of trees are characterized by their size and perimeter only, whereas spatial correlations are neglected. Coalescence of clusters is restricted to clusters of similar sizes. Our approach derives the value of the scaling exponent <i>τ</i> of the event size distribution directly from the scaling of the accessible perimeter of percolation clusters. We obtain <i>&tau;</i> = 1.19 in the limit of infinite growth rate, in perfect agreement with numerical results. Furthermore, our approach predicts the unusual transition from a power law to an exponential decay even quantitatively, while the exponential decay at large event sizes itself is reproduced only qualitatively.

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