Practice of multiple risk operation in multi-objective optimal operation of cascade hydropower plants: A case in lower branch of Lancang River Basin

[Display omitted] •5 risk factors are determined from social-economic and ecological benefits.•Thresholds for risks of cascade hydropower plants operation are proposed.•Multi-risk multi-objective cascade operation model are established.•It is concluded the results of multi-risk model are better than single-risk model. In the process of joint operation of cascade hydropower plants, the existence of risks is inevitable. To investigate the risks and make them controllable, some works were undertaken. Firstly, cascade hydropower plants in Lancang River Basin are selected as the study objects for unbalance between social-economic and eco-environmental benefits. Secondly, to clarify the multi-objective operation of cascade hydropower plants, a multi-objective model (Model-I) and a single-objective model (Model-II) were constructed, Entropy Weight (EW) method, Grey Correlation (GC) method, and the improved genetic algorithm (IGA) are adopted to solve the model. Thirdly, five risk factors from the multi-objective operation process were determined, Monte Carlo (MC) method is applied to simulate the runoff and the thresholds for risk factors were estimated by running Model-I, the thresholds are divided into three intervals by Fisher Optimal Segmentation (FOS) method. Finally, to control risks within a certain range, the risk operation model (Model-III) is constructed bellow the tolerable risk level, and the scenarios consider single-risk and multi-risk are proposed. The results show that the control of a single risk cannot manage the whole risk condition in the cascade hydropower plants operation system. Whereas in Scenario 5, except that risks for output and the abandoned water are not the lowest, other risk factors are the lowest. In conclusion, the results of multi-objective operation model considering multi-risks are better than those of the single risk in the control of risks, which provides a technical support for the decision-making of reservoir management.