Model

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view/download model file: Fire4.nlogo

WHAT IS IT?

This project simulates the spread of a fire running through a field that has been started by a lightning strike at a particular location. It shows that the time it takes and the percent of land burned by the fire are a function of the density of grasses present (in this case - Lovegrasses), humidity at the time of the strike and wind direction but not it's magnitude.


HOW IT WORKS

The fire starts at the center of the field and spreads in the direction of prevailing wind selected (standard cardinal and intermediate directions).

Our model assumes that the wind is constant in the direction chosen and that the fire spreads in this direction. It also assumes that there is grass present that can be burned and that if they have already been burned they cannot be burned again.

Our model also makes generalized assumptions regarding humidity level. We have programed it to represent three levels of humidity: high, medium and low. It allows for various rates of spreading based on the amount of humidity present at time of strike.


HOW TO USE IT

Select your desired density (% of grass coverage) slider, Wind direction (standrad cardinal and intermediate directions) and Humidity level (high, medium or low).
(Note: Changes in the Density slider, Wind direction pulldown and Humidity level pulldown do not take effect until the next SETUP.)

Click the SETUP button to set up the grass (green), fire (red at the center of view) and an arrow to indicate wind direction.

Click the GO button to start the simulation.

The DENSITY slider controls the density of grass in the field.

The HUMIDITY chooser controls whether the humidity is high (low burn response), medium (higher burn response) or low (high burn response).


THINGS TO NOTICE

When you run the model, how much of the grass burns? If you run it again with the same settings, does the same amount of grass burn? How similar is the burn from run to run?
The density of the grass during the runs should also have an effect on the way the wildfire progresses or not, how does that density therefore effect the time it takes to burn the field.

Some other things to consider is how does the amount of humidity effect the burning process, slower or faster? Does the cardinal direction chosen effect how fast the field is burned within the various humidity settings?

Each turtle that represents a piece of the fire is born and then dies without ever moving. What each turtle does is looks at its neighbor, determines whether or not it is "ready" to be burned, if it is ready to be burned then a new turtle is born and runs through the same process. (We have called this "generational transfer" and it explains why if the fire is made of turtles but no turtles are moving that the fire appears to move).


THINGS TO TRY

Set the density of grass at various levels to determine how much is needed to have a complete burn. If the grass is not a consistant cover will the fire spread or die out?

Set the humidity at various levels to determine what effect it has on the grassland itself but ultimately the start of fires due to lightning, fry or otherwise.

Set the wind direction to one of the standard cardinal and intermediate directions to see if this effects how longs it takes to burn the entire field.

Try setting up and running a BehaviorSpace experiment (see Tools menu) to analyze the percent burned at different grass density levels and different humidity livels.


EXTENDING THE MODEL

Change the wind to include magnitude (speed at which it travels)from the various directions to increase the rate at which the field is burned through.

The addition of topography to illustrate how land variances effects the overall change in burning would also be of interest.


NETLOGO FEATURES

Unburned grass is represented by green patches; burning grass and wind direction are represented by turtles. Three breeds of turtles are used, "fires", "embers" and "winds". When the grass catches fire, a new fire turtle is created; a fire turns into an ember every three ticks (turns). Notice how the program gradually darkens the color of embers to achieve the visual effect of burning out. The wind drives the fire in the direction selected. Humidity levels effect the number of ticks between each new fire generation starting to "die" and inversely effect the rate at which embers darken.

The wind direction sets a related degrees within a unit circle and is used to determine the general direction of fire spread. The "neighbors4" primitive is used to spread the fire in a more natural configuration every third generation.

You could also write the model without turtles by just having the patches spread the fire, and doing it that way makes the code a little simpler. Written that way, the model would run much slower, since all of the patches would always be active. By using turtles, it's much easier to restrict the model's activity to just the area around the leading edge of the fire.


RELATED MODELS

Fire, Percolation, Rumor Mill


CREDITS AND REFERENCES

Portions of the code for this model were taken from the Fires model in the Netlogo Models Library under Earth Science copyrighted: Wilensky, U. (1997). Netlogo Fire Model. http://ccl.northwest.edu/netlogo/models/Fire. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.