Future hydrological extremes, such as floods and droughts, may pose serious threats for the livelihoods in the upstream domains of the Indus, Ganges, Brahmaputra. For this reason, the impacts of climate change on future hydrological extremes is investigated in these river basins. We use a fully-distributed cryospheric-hydrological model to simulate current and future hydrological fluxes and force the model with an ensemble of 8 downscaled General Circulation Models (GCMs) that are selected from the RCP4.5 and RCP8.5 scenarios. The model is calibrated on observed daily discharge and geodetic mass balances. The climate forcing and the outputs of the hydrological model are used to evaluate future changes in climatic extremes, and hydrological extremes by focusing on high and low flows. The outcomes show an increase in the magnitude of climatic means and extremes towards the end of the 21st century where climatic extremes tend to increase stronger than climatic means. Future mean discharge and high flow conditions will very likely increase. These increases might mainly be the result of increasing precipitation extremes. To some extent temperature extremes might also contribute to increasing discharge extremes, although this is highly dependent on magnitude of change in temperature extremes. Low flow conditions may occur less frequently, although the uncertainties in low flow projections can be high. The results of this study may contribute to improved understanding on the implications of climate change for the occurrence of future hydrological extremes in the Hindu Kush–Himalayan region.

The selection of general circulation models (GCMs) with high capability to represent the past and likely future climate for a specific geographical location is a crucial step to assess impacts of climate change on different sectors. This study included pool of 105 and 78 GCMs for representative concentration pathways (RCPs) 4.5 and 8.5, respectively, from Coupled Model Intercomparison Project-Phase 5, applied an advanced envelope-based selection approach to select representative GCMs for the Koshi river basin in China and Nepal at short-term (2016-2045), mid-century (2036-2065) and end-of-century (2071-2100) periods, and developed range of possible future precipitation and temperature scenarios with high resolution downscaled data (10 × 10 km 2), which is the novelty contribution of the study. Considering RCP4.5, average annual precipitation is expected to increase by 0-16%, 4-23% and 4-24% in the short-term, mid-century and end-of-century periods, respectively. Using RCP8.5, equivalent predictions are 6-20%, 6-36% and 13-49% in the shortterm, mid-century and end-of-century periods, respectively. Average annual temperature is expected to increase, but with higher increases during winter than in the monsoon period. Considering RCP4.5, average annual temperature is expected to increase by 1-1.4 C, 1.3-1.9 C and 1.6-2.8 C in the short-term, mid-century and end-of-century periods, respectively. Similarly, using RCP8.5, equivalent predictions are 1-1.6 C, 1.8-2.9 C and 3.1-5.6 C in the short-term, mid-century and end-ofcentury periods, respectively. The ensemble mean of absolute change in average precipitation and temperature projects that High Himalaya and Tibet regions are more sensitive to climate change considering precipitation and temperature, respectively. The results also suggest that GCMs selection for a catchment varies with climate scenarios and specific future time periods.

This study assesses climate change impacts on the hydrological regime of a river basin and its implications for future irrigation water availability in the Koshi River basin using RCPs 4.5 and 8.5 over short-term (2016-2045), mid-century (2036-2065) and end-of-century (2071-2100) periods. Average flow in the Koshi River is projected to increase. Projections of average minimum monthly river flow suggest that the areas of winter wheat and monsoon paddy rice could be increased. However, the planting period of paddy rice should be delayed by one month (July to August) to capture the expected increased water availability in the river.

We present a systematic framework to assess sustainable hydropower potential. • The framework assesses theoretical, technical, economic, and sustainable potential. • It combines 30 datasets to represent natural, legal, disaster and social constraints. • Including these constraints in early assessments can improve hydropower decisions • The framework helps balance SDG7 (energy) with the linked SDGs 2 & 6 (food, water).

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