Impact of global climate change induced variations in reservoir-river systems on fish habitats.

Global climate change (GCC) and reservoir operations impact basin-scale hydrological conditions, altering river-scale hydrodynamics and aquatic habitats. This study designed a numerical evaluation methodology framework that integrates GCC, downscaling, hydrological, hydrodynamic, water temperature (WT), and habitat suitability models across global, basin, river, and habitat to predict the impacts of GCC on the hydrology and aquatic ecological environment of the reservoir-river system (RRS). The framework was applied to the Xiaolangdi Reservoir (XLDR) and its downstream river reach. In the study area, runoff, water level, WT, and weighted usable area (WUA) were predicted for the baseline and four scenarios, and the impact of GCC on the inflow, WT, and WUA of the RRS was evaluated. The results proved that the Soil and Water Assessment Tool (SWAT) model, the statistical downscaling model (SDSM), three-dimensional (3D) and two-dimensional (2D) hydrodynamic, and WT models met requirements. Runoff remained sufficient to meet system demands under the four GCC scenarios. WT surface, middle, and bottom in the XLDR showed increasing trends. Compared to the baseline scenario, the decrease in WUA for the spawning and juvenile Yellow River carp (Cyprinus carpio haematopterus) (YRC) was mainly influenced by hydrodynamic conditions and rising WT changes. The impacts of GCC were likely to exacerbate the adverse effects of reservoir regulation on YRC’s breeding season.