2.4. Hydrological modeling
SWAT+ is a multidimensional (deterministic) physical model that can calculate the process using a wide array of input parameters. A digital elevation model (DEM) of both catchments was prepared with a 10 m resolution. Subbasins (microcatchments) are still delineated during model construction in SWAT+, but they are subsequently divided into water areas and one or more landscape units and land uses (Figs. 2 and 3). Meteorological data were purchased from the Institute of Meteorology and Water Management in Warsaw, and the CORINE Land Cover 2018 data was used to prepare the GIS layers. The QGIS version 3.16 software was applied to create detailed soil, agricultural, and lithological maps. According to the DEM, the delineation of watercourses and subcatchments was made from raster data. The yield point of the material was determined by the soil moisture, which determines the stability of the mountain slope. The Sequential Uncertainty Fitting (SUFI2) procedure was utilized to calibrate the SWAT+ model with multiannual meteorology data (1991–2020). A SWAT-CUP4 model was used to calibrate the SWAT+ model with multiannual weather data. Optimum variables of the model structure were chosen for the physical and geographical conditions and visualized on the maps. The following parameters have been calibrated: TSS, N-NO3-N-NO2-, N-NH4+, and P-PO43- (Supplementary Table S1).