The Bagmati River Basin is the most water-stressed basin in Nepal as evidenced by increasing shortages in available water resources (surface and groundwater) to meet the basin water demand at key locations and time (mainly dry season). Bagmati Irrigation project is the national pride project of Nepal, which been providing irrigation service to farm land in Terai, Nepal. Project has envisioned to inter basin water transfer through diversion tunnel (67 m3/sec) from Sun-Koshi to Bagmati basin, to provide irrigation service all year around. After completion of project it covers the gross command area of 122000 ha.

CRAWFORD Model has been used to model the Bagmati Basin. Model was calibrated for 2000-2013 in NSE 0.81 PBIAS 11.38 and 0.92 and validated 2010-2013 had 0.501, PBIAS 40.36 and R 0.60.The study has employed warm-dry scenario of CMIP6 projection from the NESM, Global Climate Model (GCM). Hindcast data from 2000-2013 and Forecast data from 2030-2050 has been used for study. For future performance water surplus/deficit to irrigation system was assessed. Total number of water deficit month in climate of 2030-2050 is found to be increased from baseline period. However, Reliability score was found to be 92.06 and 92.46 was found for SSP 245 and SSP 585 scenario.