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Sunday, June 11, 2017

Cellular Automata Laboratory: Forest Fire Model

I have just added a new sample rule to Cellular Automata Laboratory (CelLab): Forest, a model of forest fire propagation originally published by Drossel and Schwabl in 1992.

Cells in the map represent either a tree or open ground. Lightning strikes cells at random with a probability f (default 0.00002) on each generation. If lightning strikes open ground, nothing happens, but if it strikes a tree, on the next generation the tree will be on fire. A tree on fire becomes open ground in the next generation. A tree catches fire if any of its eight neighbours is on fire. New trees appear in open ground cells with a probability p (default 0.002).

When the density of trees is low, most lightning strikes empty ground or burns only one or a few trees. As the density of fuel grows over time, the forest becomes susceptible to cataclysmic wildfires which burn large regions. Eventually, you will see lots of small fires and a few very large conflagrations.

The behaviour of the model is highly sensitive to the ratio of the parameters f and p, which you can adjust by editing the top of the evaluator function. Counter-intuitively, reducing the number of lightning strikes increases the number of large fires because it allows fuel to build up which permits the rare fire, once started, to propagate widely. This phenomenon is observed in forestry and is managed by controlled burns.

An age counter is used to display trees in sixteen intensities of green based upon their age in generations, and to make flame fronts fade after they have passed. This is simply to make the display easier to understand; it plays no part in the behavior of the rule.

Run the Forest rule in CelLab

Posted at June 11, 2017 13:48