## 2 Materials and Methods
### MIKE SHE Model Setup  
The MIKE SHE model uses different process-oriented components to describe the hydrological cycle by coupling the UZ and SZ, as shown in Table 3. MIKE SHE uses three different methods to account for UZ flow simulations, named as two-layer UZ method, Richards equation, and gravity flow method. The MIKE SHE model uses the Kristensen-Jensen method [43] to estimate the ET and interception processes by using climatic and vegetative data. Due to the computational time constraints, a simplified two-layer water balance method was used to estimate the UZ flow based on the formulation provided by [PERSON] and [PERSON] [46]. The main objective of the module is to compute the ETa and the volume of GW recharge and is mainly advantageous in areas with a shallow GW table (e.g., wetlands where the ETa is nearly equal to the reference ET rate). In catchments with higher UZ depths, the two-layer UZ method does not precisely characterise the UZ flow dynamics. The two-layer UZ method considers only the average conditions and does not account for the UZ hydraulic conductivity and soil moisture content relationship, and hence does not consider the soil ability to transport water to the plant roots. That means if sufficient water is available in the root zone it will be available for ET. However, by calibrating the input parameters, the two-layer UZ method performs quite well in \begin{table}
\begin{tabular}{l c c} \hline \hline
**Land Use Class** & **Avg. RD (Summer) (mm)** & **Avg. RD (Winter) (mm)** \\ \hline Arable land & 600 & 200 \\ Wetlands & 300 & 300 \\ Grassland & 300 & 100 \\ Industry & 600 & 600 \\ Forest & 800 & 800 \\ Orchards & 500 & 500 \\ Settlements & 600 & 600 \\ Parking surfaces & 600 & 600 \\ Water surfaces & 0 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average RD during the summer and winter season in Tollense river basin [45]. Figure 5: Average monthly variation of leaf area index used in Tollense river basin [44]. most of the conditions. The defined method takes into account the processes of canopy interception, ponding, and ET and considers the whole UZ to consist of two layers representing average conditions in the UZ, where vegetation data is defined as LAI and RD. The soil properties are defined by a constant infiltration capacity, soil moisture content at wilting point, field capacity, and saturated water content. The two-layer UZ method fulfils the main objectives to account for ETa and the SZ recharge mainly required in this study. The MIKE SHE model uses the 3D-Boussinesq equation to simulate the SZ flows [36], while river hydrodynamics (stage and discharge) are defined by using the simplified diffusion wave approximation of the Saint-Venant equation. Due to the limited ability of MIKE SHE to simulate the hydraulic structures and their operations, MIKE 11, a 1D-hydrodynamic model, was used to incorporate the control structures such as the weirs, sluice, culverts, gates, etc., and their time varying operations. The MIKE SHE model used in this study uses the \"ETRS_1989_UTM_Zone_33N_8 stellen\" coordinate system in metric units. The performance of the hydrological model was evaluated at different grid sizes (20, 50, 100, 200, and 300 m) and a spatial resolution of 100 m was selected as an optimum compromise between computational time and model performance. The model area of 400 km\({}^{2}\) was divided into 100 \(\times\) 100 m computational cells to represent the spatial variations in soil, land use, and geology. Model area was divided into computational grids in order to have the numerical solutions of the governing equations [49; 50; 51]. DEM with a resolution of 5 m was used to represent the topography in the study area and was provided by LUNG-MV. In case of temporal discretization, the computational time steps were chosen in such a way that OL-flow computational time step is always less or equal to the UZ time step, while the UZ time step is always less or equal to the SZ time step.