Calculating a topographic index
As the topography defines and influences most of the processes that take place in a given terrain, the DEM can be used to extract many different parameters, which give us information about these processes. This recipe shows you how to calculate a popular one, which is called the Topographic wetness index, which estimates the soil wetness based on the topography.
Getting ready
Open the DEM that we prepared in the Preparing elevation data recipe.
How to do it…
Calculate a slope layer using the Slope, aspect, curvature algorithm from SAGA in the Processing Toolbox option. Calculate a catchment area layer using the Catchment area algorithm from the Processing Toolbox option. Note that you must use a sink-less DEM, such as the one that we generated in the previous recipe with the Fill sinks algorithm.
Open the Topographic wetness index algorithm from the Processing Toolbox option and fill it in, as shown in the following screenshot:
Run the algorithm. This will create...
