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).