Runoff Projection for Alpine Basins Using Combined Hydrological Models: A Case Study of the Datong River Basin in the Northeast Tibetan Plateau of China

Climate change is profoundly altering hydrological processes in alpine regions, which are acutely sensitive to warming; however, accurate projections of hydrological fluxes, notably runoff, remain challenging. In this study, six hydrological conceptual models and their combinations were first evaluated through comparative experiments for daily runoff simulation. Downscaled CMIP6 climatic variables were then used to drive the selected model/combination for future runoff variations using the Datong River Basin on the northeast Tibetan Plateau, China as a case study. The results indicate that: (1) among the single and combined models, the IHACRES-CMD and GR4JSG combination has shown satisfactory performance for runoff simulation in alpine basins; (2) future projections of climate and hydrological variables based on the selected model driven by CMIP6 outputs reveal a consistent warming-wetting tendency, with mean annual temperature, precipitation and runoff increasing by 1.6°C–3.8°C, 25.5–55.8 mm, and 0.8 – 1.4 billion m 3 , respectively, under various Shared Socioeconomic Pathways (SSP) scenarios between 2015 and 2100 relative to the historical period; and (3) runoff changes also demonstrate significant future hydrological shifts, showing increased interannual runoff but a more uniform intra-annual distribution, manifested through reduced runoff in July but increase in June. In addition, results also show larger runoff variability with increased occurrence of above-normal runoff in the future. These changes imply an elevated flood-risk potential during early summer, which poses a significant challenge to existing reservoir operation rules, necessitating adaptive strategies and climate-resilient allocation frameworks for water resource systems in alpine basins.