Abstract Understanding the potential impact of anthropogenic climate change on the hydrological regime of the Koshi River Basin (KRB) is very important for sustainable water resources and ecosystem management. The hydrological studies are mainly focused on the annual, seasonal, and peak flows of the hydrological regime; however, the ecologically relevant flows of the hydrological regime are less explored. In this study, we analyzed the different flow characteristics based on the magnitude, intensity, and duration using the Indicator of Hydrologic Alterations (IHA) under the influence of shared socio-economic pathway (SSP) scenarios. We found that the KRB will experience a shift in hydro-climatic events, an increase in rise and fall rates of flow, increase in monthly low flows of the hydrological regime, eventually affecting the livelihoods and ecosystem of the basin. This study highlights the importance of environmental flow components (EFCs) in a hydrological regime to better understand the flow characteristics during the future hydro-climatic variability.