2.4.1. DEM: Topographic Effect and Use in Both Models

In the CORINE model, DEM is used to extract the topographic parameter by means of slope computation. The slope angles of the study area were obtained using the "slope" tool of ArcGIS. Subsequently, the slope raster was classified, with respect to the CORINE's model indices, into (1) very gentle to flat (<5%), (2) gentle (5%–15%), (3) steep (15%–30%), and (4) very steep (>30%).

In SWAT, the DEM is used for the extraction of the topographic parameters and for representing the basin's physical parameters such as slopes, flow direction and accumulation, delineation of the hydrologic network, and basin partitioning [67]. After inputting the DEM into SWAT, the basin was initially divided into 25 sub-basins using SWAT's watershed delineator. However, given the presence of a great number of waterbodies, and their impact on output accuracy, the number of sub-basins was increased to 35. The purpose of increasing the sub-basins' number was to increase the spatial resolution for a more detailed representation of the basins' processes [68]. Since the SWAT model allows only one pond per sub-basin [39] during the sub-basins' delineation, the largest number of ponds was included in each in order to ensure maximal representation of pond-induced processes. Further, all ponds within each sub-basin were lumped and the outlets of the sub-basins were chosen to coincide with those of the ponds in order to maximize their representation and account for their effect. The SWAT delineated hydrologic network was, in turn, verified against a pre-defined stream network in order to ensure and improve its accuracy.
