Application of YHyM/BTOPMC to evaluate hydrological response of Kali Gandaki River Basin (KGRB) in Western Nepal

Snowmelt runoff is an important source of water resources in the mountainous basins of Nepal. Modeling snowmelt runoff is challenging especially when snow observations are unavailable. In order to overcome the data shortage, YHyM/BTOPMC, a physically-based distributed hydrological model integrated with a simple degree-day based snow accumulation/melt sub-model was applied to evaluate hydrological response of Kali Gandaki River Basin (KGRB) in Western Nepal. It is apparent that temperature in Nepal is increasing, progressively higher for high elevations and precipitation is becoming more erratic. Hence, the snowmelt process, river runoff and water availability in KGRB is sensitive to the increasing climate change. The objective of this study is to assess the hydrological response of the basin to different climatic perturbation. Assessing the runoff pattern/water availability situation is very important in flood risk management, water use planning and in overall management of water resources. Public domain global data along with daily measured temperature and rainfall data were used in this study. The model was calibrated and validated using daily observed discharges and the stream flow in KGRB can be predicted with an acceptable degree of accuracy. The model performance was tested through the Nash-Sutcliffe efficiency objective function and by the volume ratio of simulated to observed discharge. Annual temporal variability of stream-flow was also plotted to ensure the response of KGRB to temperature and precipitation changes.