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 exactly 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 supression activities.
What helps fires spread is largely dependent on how much fuel there is in the landscape, how dry it is and the 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 (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
- Cliff lines. Along ridges and escarpments. It is difficult for fires to jump up cliffs and they are also associated with rocky/low fuel regions.
- 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 esacping.
In this exercise we will make a map bringing together these main features. Skip to video.
We will continue working on Dambi north country by first looking at all of the areas that burnt early in the year. This is using higher resolution imagery than the NAFI data. This was produced by the Darwin Center for Bushfires Research using Sentinel-2 Satellite data. Using this Satellite we have mapping at a 20 meter resolution (compared to 250m for NAFI).
For this excersice we will start a new project.
Open the Early dry season mapping file. You will notice it has the extension .shp on the end of the name. this means it is a shape file which is vector data.
Now open your protected area boundary layer again. You should see something like this:
Change the protected area fill to ‘no brush’ the same way we did it in the previous exercise. Then change the color of the burnt areas to a dark red color.
You will get a map somthing like this:
For interest now use the NAFI plugin to open the 2020 NAFI mapping for the same area.
You will see, shown below by arrows, areas that the fine scale mapping shows that are gaps in incedndiary burns show up as solid burnlines on NAFI. Also NAFI has missed some fires, shown in the red box.
This highlights why it is important, where possible, to use higher resolution data when planning your burning or thinking about suppression.
Now add watercourse, escarpment, roads and infrastructure layers.
When you first load all the layers it will not look very good. You need to change the colours and order of the layers to produce a map that is easy to understand.
For example lets change the symbology of the water courses. Double click on the water layer and
- select the symbology display.
- Choose the display type to “Categorized”
- The value to make the “Hierarchy”
- Click classify to create a line colour and for each water course hierarchy category.
We can further improve the display by changing the colour and line width of the major and minor water courses. For example make the colour of the major water courses darker and the line width larger for the Major water courses. Also change the line colour for the minor water courses to a lighter blue but do not change the line width.
Also change the colour of the escarpment cliffs and the transparency of the hill shade layer.
We are now starting to develop a bit of a picture of the landscapes and barriers to fire spread as well as how effective our early dry season burns have been.
For example in the image below you can highlight (shown as red lines) where there are gaps in the prescribed burn lines and opportunities to augment the stopping power of some cliff lines to draw a fire containment area. These maps can help you plan your future burns.
Now lets add the fires from the previous year, they also provide a good indication of available fuel in the landscape. The three files in the 2019 folder are for burnt areas earlier in the year (before June), the middle of the year, (Between June and September) and late in the year which includes everything after September. Load all three layers.
You now have a quite a few layers displayed. To make it easy to see all the layers along with the 2019 burnt area layers change the fill transparency.
..and change the stroke style to “No Pen”
You should have a map something like this. This further enables us to see the risks and and opportunities for fire management.
You will notice that there where no mid- dry season burns in this country. Those late dry season burns are also likely to have less fuel than other parts of the landscape.
To help locate yourself in the landscape add lables to the infrastructure points. Double click on the infrastructure layer and
- open the label display.
- set label type to Single Labels
- The value to “Names”
- The font size to 12
- Then select ‘mask’
In the Mask display click the “Enable Buffer” check box. This will draw a white boarder around the text making it easier to see.
You can now see the locations you might be able to use as bases to assist your burning program.
Finally, you can overlay the NAFI fire history maps that we created in the previous exercise to identify areas that have not burnt for a long time that need careful consideration and areas that burn very frequently that may show country that grows a lot of fuel quickly.