What spreads fires?
What are the risks and opportunities for fire control?
These are key questions that support fire mitigation and suppression work. Maps can help us answer them.
Although it will always be difficult to predict exactly how a fire will behave we do know what is likely to help fires spread and what might stop fires. These are also things we can map to help us decide where we should burn and to help us with suppression activities.
What helps fires spread is mainly dependent on how much fuel there is in the landscape, how dry it is and the weather conditions (wind, temperature and humidity). We can not use GIS to map fire weather but it can give us a good idea of current fuel conditions. Fuel loads are related to the type of grass vegetation and the time since it last burnt.
So what stops fires:
- Burnt areas. Obviously, country that has already burnt will have little fuel to carry a fire. Even some (e.g., spinifex) country that burnt the previous year may not have enough fuel the following year.
- Roads and fences. These are important lines in the landscape often with no or low fuel.
- Watercourses. Rivers most of the year and creeks, when they are wet, can be effective barriers to fire spread
- Wetlands/Mangroves and mudflats.
Making maps of the location of all of these features can help us think about how we manage the land to minimise fires escaping.
In this exercise, we will make a map bringing together these main features. Skip to video.
We will also look at an example burn plan and how we can add new burn lines.
Creating a Burn Plan Map
Start by loading the high-resolution fire mapping for the last two years. These data are developed using satellites that provide a much better view of burnt areas than that shown on NAFI.
Double click on one of the new Tiwi burnt area layers to open the symbology window:
- Chose the render type ‘Paletted/Unique Values‘ using the drop down menu
- Click Classify to shown the colours for each value
- Value 0 = no fire
- Value 1 = early dry season fire
- Value 2 = late fire
We will change the colours so the make more sense:
- Value 0 = make no colour
- Value 1 = blue
- Value 2 = red
Double clicking on a colour box enables you to change the colour:
Use the opacity slider to make the value 0 transparent.
These colours helps us see the difference between early season controlled burns and late season wildfires.
Do this also for the 2021 burns and notice the different outcomes.
Now make the burn colours a light grey and turn off the satellite layer so so they do not interfere with the other layers we are now going to add:
Now start adding other layers showing where fire will and or should not burn. Start with the mangrove and mudflat layers and change the colour;
- Double click on the layer to open the symbology window
- Change the simple fill
- Change the colour
- Select a colour
- Click ok
Do the same for the plantation layers but make it green:
Now add the watercourses. Make the watercourses different colours based on their size:
- Choose ‘Categorised‘ as the display type
- ‘Hierarchy‘ as the value
- ‘Classify‘ to show the categories
- Change the line colours – select dark blue for major and light blue with some opacity for minor.
Finally add the roads and make them red.
Also add the infrastructure layer to show things you want to be careful no to burn.
This map can help to guide when you want to put in this years burn lines.
Some burn draft plans are provided, load them and change the symbology based on the type of burn (Road, helicopter and on-foot – infrastructure). Something like this:
You can add new burn lines using the edit and add line features buttons.
Once you have pressed these buttons you can draw a new line:
Left click to draw a line – right click to finish a line. When a line is finished you can add the type of burn it is:
You will notice that this layer also has the attribute timing. This allows you to add information about when you think would be a good time to do this burn – i.e. “early April”.
If you have a lap-top with an inbuilt GPS or plugin GPS you can use this map to navigate in from a car or air when you do the burn runs.
Right click on the top panel in QGIS and enable the GPS plugin:
The following panel will appear.
You can also export this map as a PDF that can be used in Avenza maps for a mobile device. This is covered in the next section.