A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management

Thesis (M. Eng.) - Asian Institute of Technology, 2014

The study was conducted to assess the impact of climate ch ange on Melamchi Water Supply Project (MWSP) which is still in its construction phase. MWSP is a multimillion dollar project designed to minimize the deficit of drinking water in the Kathmandu valley. The constr uction of the project started in 1998 which w as schedule to complete by 2008. But, due to various problems the project is still in its early stage. In the last ten years, the population of Kathmandu valley has increased by 1.5 times and is predicted to reach 5.28 million by 2050 which will consequent ly increase the water demand in the days to come . This research quantifies the future water supply and demand in Kathmandu valley under climate change impact. The Soil Water Assessment Tool (SWAT) was used in hydrological analysis. The model was calibrated and validated at two point; Melamchi sub - outlet and Indrawati Basin outlet. The model showed good performance of daily simulation with R 2 and NSE > 0.75 for ca libration in both the outlets. For validation however , the model perform ance was lowered but satisfactory with R 2 and NSE > 0.55 for Melamchi sub - outlet w hereas , for Indrawati basin outlet R 2 and NSE was >0.85. In all the cases PBIAS and RSR was less than 15% and 0.7 respectively. The ensemble of 4 climate models (HadGEM3 - RA, Reg CM4, MIROC_ESM and MRI - CGCM3) predicts that the future temperature in Indrawati Basin will increase by 2.5 0 C to 4.9 0 C by the end of the century. Precipitation will decrease during 2 060s and 2080s under RCP 4.5 where as it will increase under RCP 8.5. Calibrated SWAT model was run to simulate the future stream - flow of Melamchi, Larke and Yangri Rivers. The result shows an increase in annual s tream - flow for all the rivers but t he disch arge in the rivers will be just enough to divert water to Kathmandu valley during dry season. Four case s a) pessimistic future , b) moderate I future c) moderate II future and d) optimistic future were developed to analyze water supply and demand. Even with the purposed MWSP, the number of people without access to pipe water will be 1.63 million by 2050s and 1.71 million by 2090s. With proper demand management deficit in the valley can be decreased drastically.