Integrated MIKE SHE/MIKE+ modelling and isotopic investigations for freshwater assessment of the Suketi catchment in the Northwest Himalayas

Reducing the unrealistic simulations of different hydrological models is necessary for precise water assessment and flood forecasting. The scarcity of observed hydro-meteorological data in mountainous catchments further hinders the model's efficiency in water evaluations. This study aims to estimate the freshwater availability via characterizing the water balance employing a distributed MIKE System Hydrological European (SHE) model for the Suketi catchment of the Beas Basin, in Himachal Pradesh, India. For this purpose, the MIKE SHE/MIKE+ based model was developed for the study area using meteorological and basin-specific data. The collected samples from the rainfall, groundwater, and stream water during 2023-2024 were analysed for stable water isotopes, i.e. δ¹⁸O and δ²H. The quantitative evaluation established the efficacy of the MIKE SHE/MIKE+ based model with root-mean-square-error, coefficient of determination, Nash-Sutcliffe efficiency, and percentage bias of 76.67, 0.88, 0.92, and -0.32, respectively. The output of the developed model was integrated with the results of a two-component mixing model through the measured values of δ¹⁸O and δ²H. The local meteoric water line (LMWL: δ²H = 8.17 · δ¹⁸O + 13.11) reveals the different climatic conditions due to lower temperatures and higher latitude of the study area vis-a-vis global average. The validated water balance of the Suketi catchment infers adequate freshwater availability in the catchment with more than 74 % as baseflow to the Suketi river and evapotranspiration accounted for 64.42 % of water loss into the atmosphere.