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Abstract

This study explored the impact of climate change on the Hydrologic Alteration in the Himalayan River basin i.e., Koshi River Basin, Nepal. The bias-corrected and downscaled coupled model Intercomparison Project (CMIP6) models from 2015 to 2100 with four climate models (BCC, CANESM-CCCma, CNRMCM-CERFACS, and IPSL) under two shared socio-economic pathways (SSP2-4.5 and SSP5-8.5) were used for the climate change analysis over Koshi River Basin. The Soil and Water Assessment Tool (SWAT) model was first calibrated (1985-2006) and validated (2009-2012) at a daily timescale for simulation of streamflow. The past, present, and future potential streamflow responses to climate change were analyzed for various flow indicators. The Indicator of Hydrologic Alterations (IHA) was used to calculate the different flow parameters i.e., IHA parameters and ecological flow parameters (EFCs) based on the magnitude, intensity, and duration. The summer rainfall and winter temperature of the basin expect to increase by more than 20% which indicates the risk of extreme climate events in the future. Similarly, climate change is expected to increase the maximum monthly streamflow, especially from June-September with the potential for extreme flow events in the Koshi River Basin. The reported changes in rainfall, temperature and streamflow will help to understand the extremities of climate and hydrological variability of Koshi River Basin and will help to provide strong policy implications and adaptation measures against natural hazards.