A powerful feature of raster data is the ability to conduct mathematics using multiple datasets. For example, adding multiple burnt area raster layers together, we can produce fire frequency information giving new insights into the fire regimes of a region.
Fire history analysis using raster math.
In this section of the tutorial we will create fire history metrics for Kakadu National park using raster data from the North Australia Fire Information Website;
Load all of the downloaded raster fire data into QGIS using the file browser.
Clip each fire raster to Kakadu the same as you did for the elevation data. This time set the output data as a file to save into a ‘working’ directory:
As you clip each fire dataset give it a name as shown below.
You should end up with data layers like this:
An important metric for understanding fire management outcomes is the frequency of hot late dry season fires. We will create a late dry season fire frequency layer for Kakadu. To do this we first need to reclassify each layer giving Early Dry Season fires the values of 0 and Late Dry Season fires the value of 1
Use the reclassify raster tool as you the same as used on the elevation data-set except classify the data as shown. (Months 0-7 a value of 0 and months 7-12 a value of 1.)
As you produce each new LDS dataset name them by year and reclassification type, i.e. FS2014_LDS, so you know what each layer is.
Now use the raster calculator tool to add all of the reclassified LDS layers together as shown below.
Display the final Late Dry Season Fire frequency using a colour ramp similar to that shown here.
To get and area report for the LDS fires frequency we need to the reproject the result into GDA 94/Australain Albers as we did with the elevation dataset.
Use Raster Layer unique values to create fire history report.
Try copy and pasting the values into excel to produce a graph of fire frequency.
Finally create a LDS fire frequency report for sandstone country. Fires clip the raster dataset to the Sandstone habitat type.
Combining Raster and Vector data for analysis
First select the ‘Sandstone Woodland’ habitat type.
Use the Clip Raster By Mask Layer tool.
When you run the tool make sure you have selected feature only ticked:
Now you can report on the area of just the Sandstone country that was effected by Late season fires.