1. Institute of Hydrology, Water Resources Management and Environmental Engineering, Ruhr-Univ. Bochum, Universitätsstraße 150, 44801 Bochum, Germany (corresponding author).
2. Institute of Hydrology, Water Resources Management and Environmental Engineering, Ruhr-Univ. Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
3. Professor, Institute of Hydrology, Water Resources Management and Environmental Engineering, Ruhr-Univ. Bochum, Universitätsstraße 150, 44801 Bochum, Germany.