Impacts of 1.5°C and 2.0°C Global Warming on Runoff of Three Inland Rivers in the Hexi Corridor, Northwest China

Basin-scale projections of river runoff at different warming levels provide useful information for climate change adaptation. In this study, we investigated changes in the projected climate and simulated runoff under 1.5°C and 2.0°C global warming of three inland rivers in the Hexi Corridor: the Shiyang River (SYR), the Heihe River (HHR), and the Shule River (SLR). The change in climate was projected based on five global climate models (GCMs) under three representative concentration pathways (RCPs), and the change in runoff was simulated based on the Soil and Water Assessment Tool (SWAT) hydrological model. Furthermore, the uncertainties in projected climate change and simulated runoff constrained by the GCMs and RCPs were quantified. The results indicate that, compared with the baseline period (1976–2005), there is a 1.42–1.54°C increase in annual air temperature and 4%–12% increase in annual mean precipitation in the three river basins under 1.5°C global warming, while there is a 2.09–2.36°C increase in annual air temperature and 5%–11% increase in annual mean precipitation under 2.0°C global warming. The simulated annual runoff of the SYR decreases by 4% under 1.5°C global warming, that of the HHR decreases by 3% and 4%, while that of the SLR increases considerably by 10% and 11% under 1.5°C and 2.0°C global warming, respectively. The additional 0.5°C global warming results in an annual air temperature increase of 0.67–0.82°C, a change of −1% to 1% in annual mean precipitation, and a change of −1% to 5% in simulated runoff. The simulated annual runoff has greater uncertainty. The simulations indicate substantial and consistent warming in autumn and winter in the three basins, relatively drier summer and autumn in the SYR and HHR basins, and a relatively drier autumn in the SLR basin. The simulated monthly runoff shows more complex changes with large uncertainties constrained mainly by the GCMs.