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created with NetLogo
view/download model file: yellowstonemodel.nlogo
WHAT IS IT?
-----------
This project simulates the dynamic of fires in a forest and it's
inspired by
"Fire", a model present in the Netlogo Models Liibrary
and made by U.Wilensky (1998).
This model doesn’t take into account factors such as the
characteristics of the trees, the atmospheric conditions or the
existence of barriers, natural or artificial.
Our purpose is to create a simulation that, even without any
specification, shows the same kind of relation between dimension
and frequency of fires as observed in nature.
In our model the fires spread through the forest, burning the
patches where they can find a tree. The fires have a certain
chance to extend at the adjacent wooded areas (patches), but they
can not skip empty patches.
The final dimension of a fire depends on the density of the trees
and on placement of the initial patch.
HOW TO USE IT
-------------
Click the setup button to set up the trees (green).
Click the go button to start the simulation.
With the slider INITIAL-DENSITY you can choose the density of the
forest at the beginning of the simulation.
The slider REAFFORESTATION controls the frequency at which new
trees are planted on the unwooded areas at every period.
You can set the risk of having a new fire on a green patch with
RISK-OF-FIRE, and the chances of expansion of the fire with
PROPAGATION-PROBABILITY.
HOW IT WORKS
------------
In our model you can not have two fires at the same time. What
would happen if different fires were allowed to take place at the
same time?
With the chooser TIME-MANAGEMENT you can decide between two
different ways of dealing with the creation of new fires. The
option ONLY-ONE doesn’t allow a fire to be created, before
the last one has gone out. The option SIMULTANEOUS allows
different fires to burn at the same time.
By choosing the second option, you can control the number of
periods in which a new fire can start with CYCLES-AT-RISK out of
the total number of periods set by the slider NUMBER-OF-CYCLES.
THINGS TO NOTICE
----------------
The grey border around the edge of the screen prevents the fire
from spreading beyond the borders of the screen.
The simulation has also a graph where the dimension of fires is
plotted, so that you can immediately check the result of changing
any of the initial setting.
THINGS TO TRY
-------------
Specifically the sliders PROPAGATION-PROBABILITY and
REAFFORESTATION have been set in order to allow you to try the
effect of different policies.
Will a fire prevention policy, that lowers the chances of
expansion, have as a consequence a lower average dimension of the
fires?
EXTENDING THE MODEL
-------------------
It could be interesting to add some of these factors above-mentioned,
such as the characteristics of the trees, the atmospheric
conditions or the existence of natural or artificial barriers.
NETLOGO FEATURES
----------------
Trees are represented by green patches; burned areas and areas
where no trees have been planted are black.
The turtles are the matches that let the fire start.
Two breeds of turtles are used, "matches" and "embers".
When a match-turtle (red) is created a tree catches fire, the
adjacent trees have a certain chance (set by PROPAGATION-PROBABILITY)
to create a new match-turtle. The matches turn into embers after
a period.
Notice how the program gradually darkens the color of embers to
achieve the visual effect of burning out.
The border patches are grey to show that they can not burn for
any reason.
The data for the graph (dimension of fires) are collected at the
end of every period, if you choose the ONLY-ONE option.
Otherwise, the program will check the burned area at the end of
every NUMBER-OF-CYCLES. You should choose a NUMBER-OF-CYCLES
larger than CYCLES-AT-RISK, in order to get a sufficient number
of periods devoted to the development of fires, and to avoid the
risk of having fires still burning when the program measures the
burned area.