I am looking for a way to calculate the upstream catchment area where water would flow into a given wetland.
I have delineated the boundary of a wetland (creating a polygon) and would like to determine the upslope catchment area and downslope area of the wetland polygon. My wetland polygon is not on a stream network.
In QGIS, I used the SAGA Rasterize Tool to rasterize my polygon - making sure that my new rasterized wetland has the same projection, resolution, and extent as my DEM. Then I proceeded to use the SAGA Upslope Area tool using my rasterized wetland as the "target area," and my DEM for the Elevation. However, I keep getting the error "Input layers do not have the same grid extent."
As an alternative, I tried using Whitebox GAT using the process described in here: How to create a catchment from a point using a DTM raster in QGIS?
However, this process is for a point vector, whereas, I am looking for something that can calculate the catchment for a specific polygon or area.
I'm fairly new to using QGIS and very new to using Whitebox. I have some experience with ArcGIS as well, but don't have access to a licence.