Forth-eV Wiki

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
{{pfw:banner.png}}
===== Simulation, Forest fire =====

This program simulates the way a forest fire develops after a lightning-strike, and it shows how the fires influence the structure of a forest. The idea is based on a publication by B. Drossel and F. Schwabl, [[https://www.sciencedirect.com/science/article/abs/pii/037843719290504J|Self-Organised critical forest-fire model]], Physical Review Letters, Vol. 69, No. 11, September 1992.

The program functions as follows:

The central part of the program is a toroidal grid of 512x384 bytes. Execution starts with clearing the grid, corresponding to an area without trees.

Next an endless loop is started. In each loop the following is done:

<code>
Select a random cell in the grid
Check te content if that cell
if the content is empty
    there is a change of 1:500 that a new tree is generated
else
    if the content of the cell is a tree:
        check if any of the neighbours is a tree on fire
            if yes -> also go on fire
            if no -> a 1:1000000 change that 'lightning' causes fire
        raise the age of the tree with 1 (up to 255)
    else
        lower the age of a fire with 1 (until 0 is reached)
    then
then
update the screen for the tree or fire based on the age of the tree or          fire
next loop
</code>

The program is not very fast. Executing 10.000 loops takes between 8.5 and 10.5 ms. With a grid of 512x384 and the default settings it takes about 115 million loops) before a major forest-fire develops.

It is interesting to play around with the different settings of the program to see what happens. If you raise the chance of a lightning-strike you will see that there will be more fires, but never very big. If you raise the chance of a new tree growing there will be a high density of trees quickly, resulting in larger fires. It is also possible to raise the time it takes for a tree to catch fire from a neighbouring tree by changing the definition **(ONFIRE?)** or lowering the value **IGNITE**.

**[[https://youtu.be/JNGmbZAHrhY|Forest fire on YouTube]]**

{{https://user-images.githubusercontent.com/4964288/153408550-665f2bef-2022-4393-87c9-7bdef45b0746.jpg| Waldbrand2}}