The prevalence of wildfires and bushfires in wild vegetation like woodland, grassland, scrubland, and savannahs, as well as urban centers necessitates the need for fire risk mapping. These fires are susceptible to occur during dry or hot seasons in areas like Australia, Africa, and parts of USA (California), among many other areas.
In recent times, social agencies and government agencies have fostered the implementation of anti-fire outbreak regulations that would mitigate the excessive occurrence of wildfires that destroy lives, services, and properties. That said, the evolution of geo-mapping has contributed to the several fire risk mapping strategies by providing a proactive way of implementing fire safety measures backed by empirical evidence that addresses several Sustainable Development Goals.
Using slope, elevation, aspect, and land use to map wildfire risk
Several factors contribute to the outbreak of fires in a region. However, in this tutorial, the following factors are considered; slope, elevation, aspect, and land use.
Figure 1 below summarizes the geospatial approach and tools employed in this tutorial about mapping fire risk.
Preparation of Slope and Aspect Data
Digital Elevation Model (DEM) data for an area of interest can be accessed from United States Geological Survey’s website.
After, the following steps can be followed to derive slope from DEM:
- Open ArcGIS Pro, and create a new project from the “project” tab by selecting “blank.” From the insert tab on the menu bar, click on “New Map” to select a new base map.
- To import the DEM onto the map canvas, click on the “Add data” tool.
- From the search bar of the geoprocessing toolbox, type and search, “slope.”
- From the slope panel, set “input raster” to the DEM.
- Set “output raster” to your desired output location and name.
- Click “Run.”
To derive aspect from DEM, the following steps are followed:
- From the search bar of the geoprocessing toolbar, type and search, “aspect.”
- From the aspect window, set “input raster” to the DEM, and set “output raster” to your desired output location and name.
- Click “Run.”
Preparation of Elevation Data
The elevation data employed in this tutorial was prepared using Google Earth. Surface elevation points were collected using the “add path” tool from the menu bar of Google Earth over desired area of interest. The resulting KML file was saved to a location and given a name.
The website, GPS Visualizer, was used to convert the KML file to gpx format, and saved to an output location. For detailed guidelines, see the video link attached (Extracting Elevation Data from Google Earth – YouTube).
The gpx file was converted to layer format in ArcGIS Pro, using the following steps:
- From the search bar of the geoprocessing toolbar, type and search “gpx to features.”
- From the opened window, set “input gpx file” to the gpx file from the gpsvisualizer’s website.
- Set “output feature class” to your desired output name and location.
- Click “Run.”
The collected elevation data from Google Earth was rasterized using spatial interpolation in ArcGIS Pro.
The following steps are taken:
- Type and search, “IDW” from the search box of the geoprocessing toolbar.
- From the IDW panel, set “input point features” to the processed gpx points.
- Set “Z value field” to elevation.
- Set “output raster” to the output location and name of your choice.
- Click “Run.”
Preparation of Land Use Data
After acquiring the land cover data, the data is imported onto the map canvas using the “Add Data” tool from the steps illustrated above. Where the Landcover data needs to be streamlined to a specific Area of Interest, “extract by mask” from the “Spatial Analyst toolbox” or “clip” tool from the “data management toolbox” can be used. Steps are outlined below using “extract by mask”;
- Type and search “extract by mask” from the search bar of the geoprocessing toolbox.
- Set “input raster” to the “landcover raster data,” and “output raster” to desired name and location.
- Set “feature mask data” to the desired extent of study. Click “Run.”
Alternatively, to use the “clip” tool, the following steps are followed;
- Type and search “clip” from the search box of the geoprocessing toolbox.
- Set “input raster” to the landcover data.
- Set “output extent” to the desired extent of study area.
- Ensure that, “use input features for clipping geometry” is checked, and click “Run.”
The steps outlined above can be repeated to streamline slope, aspect, and elevation to the desired extent of study.
Reclassification and Weighted Overlay of Factors
The factors are set to a defined number of classes (three classes), using the “reclassify” tool in ArcGIS Pro. After, weighted overlay analysis will be performed by assigning weights to the factors employed in this study. To reclassify slope into three defined classes, the following steps are followed;
1. Type and search “reclassify.” Set “input raster” to the result of “slope.”
2. Click “classify,” as highlighted in yellow marker in figure 8 below and set number of classes to 3.
3. Set “output raster” to desired location and name of storage. Click “Run.”
The steps are repeated for the other factors (aspect, elevation, and land use) to reclassify them. Weighted Overlay Analysis is performed over the factors in ArcGIS Pro following the steps outlined below;
1. Type and search “Weighted overlay.”
2. The following weights are assigned to the factors in order of preference and relevance; land use = 30 percent, slope = 25 percent, elevation = 25 percent, and aspect = 20 percent.
3. Click “Run.”
The resulting raster layer can then be symbolized using the values from the remap table.