Hydrological responses and adaptive potential of cascaded reservoirs under climate change in Yuan River Basin

The ongoing cascading hydropower exploitation in southwestern China has been the subject of debate and conflict in recent years. This study aims to assess the climate change impacts on the hydropower system of Yuan River and to quantify the future potential in operation optimization of Gasa-Madushan (GS-MDS) Reservoir system. The Community Climate System Model version 4 (CCSM4) projections are bias-corrected and downscaled to drive the Soil and Water Assessment Tool hydrological model, aiming to predict the climate and runoff changes for the future. Then, an adaptive operation chart model of cascaded reservoirs is established to balance hydropower generation and ecological requirements under climate change. In the future, the decadal average temperature and annual average precipitation will possibly increase by 0.80–2.22 °C and 2.56–4.65%, respectively; the monthly average runoff may increase by 6.89%, 6.17%, and 18.26% for GS Reservoir Basin, and by 8.89%, 8.14%, and 23.14% for MDS Reservoir Basin under Representative Concentration Pathways (RCPs) 2.6, 4.5, and 8.5, respectively. The adaptive operation chart results in a reduction of 52.66–70.77% in the total water shortage at a cost of 2.09–4.54% decrease in total power generation of the GS-MDS cascaded hydropower system compared to that of non-adaptive operation chart.

Multi-objective optimization of the Three Gorges cascaded reservoirs operation with emphasis on electricity generation and ecological requirements

The operations of reservoirs produce enormous economic and social benefits but also impact species composition and habitat distribution of the riverine ecosystem. Hence, the realization of conservation and restoration of the ecosystem calls for reservoir reoperation. It is a widespread consensus that providing suitable ecological flow (SEF) for ecosystems is a useful way to cushion adverse effects. In contrast to the conventional methods that take a minimum ecological flow as a constraint, studies have been conducted to establish multi-objective operation models with an ecological objective recently. This paper considers two cascaded reservoirs: the Three Gorges Project (TGP) and the Gezhouba Dam in the middle Yangtze River. By concentrating on urgent ecological problems such as the reproduction of four major species of Chinese carp and the propagation of Chinese sturgeon, a series of monthly SEF was synthesized. Afterward, a long-term multi-objective optimization model that maximizes power generation and minimizes the water volume that violates ecosystem water requirements was developed to study the relationship between the two objectives. The non-dominated sorting genetic algorithm II method was applied to solve the proposed model. The optimized results show that according to the present water control operating regulations, the monthly amount of released water of TGP can be sufficient for ecosystem requirements except in October. The ecological model is better in improving the river ecosystem, but at the expense of power generation loss. Moreover, this method provides a set of operational non-dominated schemes between the target objectives for decision-makers to select and could be useful for water resource management of reservoirs.