FlamMap Lesson 7

Evaluating Burn Probability Outputs

Expand the MTT Burn Probability run item (by clicking the icon) in the "Tree" pane to show the output items.

There are six additional outputs included that were not listed on the Minimum Travel Time tab. The Max Spread Direction, three Elliptical Dimensions, MAXSPOT (Combined), and Run Log outputs will not be discussed in this lesson. You can find out more on these outputs by clicking on the above links.

Burn Probability

Select the ♦Burn Probabilities  output item so it is displayed and turn off the ♦ MTT Perimeters vector output. This is the most useful output and doesn't require any post-processing outside of FlamMap.

The default color ramp shows some interesting patterns of the ♦Burn Probabilities item. But the legend can be improved to further tease out more information. Right click on the ♦Burn Probabilities item and select the Properties command from the shortcut menu to display the "Create/Modify Legend" dialog.

Select the legend line just below the No Data line and click the Insert Class button. Type in 0.0000 for the value in the inserted line and leave the default black color. Your "Create/Modify Legend" dialog should look similar to this, but not exact since every run uses different ignition points.

Click the OK button in the "Create/Modify Legend" dialog to return to the project window.

Two interesting things are now visible.

• First, the black areas not burned by any of the random fires. Some of these unburned cells are due to non burnable fuel models like rock and water, other are due to the fact that none of the random fires got to a burnable cell. It is important to realize this difference since non burnable cells have a burn probability of zero, and the burn probability for the unburned burnable cells is really unknown.
• Second, notice the "shadow" of unburned and low probability cells along the windward, west edge of the landscape. This "shadow" is a common issue because cells along the windward edge of the landscape can only burn from slow backing spread since there are no ignitions upwind to burn this edge as frequently as the central part of the landscape.  

For more on MTT Burn Probabilities feature see the Random Ignitions section in the Minimum Travel Time Tab topic and the Technical Topic, Minimum Travel Time.

MTT Perimeters

The ♦MTT Perimeters contain all the final perimeters of the simulated random fires. When viewing the entire landscape this output has the look of a bowl of spaghetti and appears quite meaningless. You can zoom into a low burn probability area (gray, if you're using the default legend) of your landscape and see a few of the individual perimeters.

The real value of this output comes when you save it to a shapefile. You can then load it into a GIS to analyze individual fires or summarize the attributes.

It may also be helpful to copy this run and change the number of ignitions to a small number, 10-15, and then view the ♦MTT Perimeters .

Flame Length Probability

There are two Flame Length Probability (FLP) files, one with the flame lengths in feet (English) and one in meters (Metric). You can open these files by right clicking the FLP English item and select Open from the menu. Note that these are large files and may take a few minutes to open.

Each line represents a node on the landscape beginning at the upper left corner of the landscape or analysis area. For each node the proportion of the random fires which burned at one of the flame length (FIL) categories is listed.

Additional explanation can be found in the Flame Length Probability (FLP) file topic.

Fire Size List

The FireSizeList item is simply a list of all the random ignitions and the resulting fire size.

Additional explanation can be found in the Fire Size List File topic.

You're Finished

If you haven't already done so, you can move on to the Treatment Optimization Model lessons.