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Runoff is an important basis for the operation of hydropower. However, due to inflow uncertainty, the ideal practical operation process usually doesn't match with the plan, which exacerbates the power generation and ecological risks. Therefore, the purpose of this paper is to investigate the relationship between hydropower generation, ecology and their risks under the uncertainty of inflow. Gibbs sampling based on the copula function is presented to simulate the runoff. The scenario tree method is employed to describe the inflow uncertainty. The power generation risk operation model is developed based on the Mean-variance method. In addition, the expected minimum ecological risk model and its comparison model are proposed to analyze the relationship between power generation and ecological risk. The proposed methods are applied to a case study of the Lancang River cascade hydropower station. The results show that (1) The power generation risk of risk operation model decreased by 86.41% at the 90% scenario reduction level, compared with deterministic model. (2) There is an obvious competitive relationship between ecology and power generation, in the case of a 1% loss of expected power generation, the expected ecological risk can be reduced by 6.14%. • The Gibbs sampling model based on copula function is presented to simulate runoff. • The scenario tree method is employed to describe the uncertainty of inflow. • The Mean-variance is introduced to build the reservoir risk operation model. • The trade-off between hydropower generation, ecology and their risks of cascade hydropower stations is analyzed. [ABSTRACT FROM AUTHOR]

Global warming has caused severe regional water security risks, and from the theory of the hydrological cycle, the daily extreme temperature could also bring an impact on the streamflow volume, which could be even more important than the average temperature. Therefore, based on the level of the maximum or minimum temperature warming scenarios, a variety of meteorological datasets were selected to assess the asymmetric effect of increased daily extreme temperature on the streamflow from a multi-scale perspective by using the Variable Infiltration Capacity (VIC) model. Model simulations indicate that the streamflow experiences more significant changes in response to the maximum temperature than in response to the minimum temperature, and the relationships of streamflow with both the maximum and minimum temperatures show an upwards parabolic response function, but the response function varies with the type of warming. Additionally, the seasonal and monthly duration curves results show that the increases in both the maximum and minimum temperatures demonstrate a similar response that leads the proportion of the flood period streamflow to be increased (Tmin : 0.16–0.53%/°C; Tmax : 0.11–0.51%/°C). When the minimum temperature increases, the higher the original temperature in the region, the greater the proportion of the flood period streamflow increases. However, when the maximum temperature increases, the opposite effect occurs. • This paper included a numerical analysis of the sensitivity of streamflow to daily extreme temperature increases. • This paper discusses in detail the regional asymmetric effect of daily extreme temperature increase to streamflow. • A relatively complete picture of the hydrological processes caused by daily extreme temperature rise is presented. [ABSTRACT FROM AUTHOR]

Highlights • Consider the ecological base flow, fish habitat flow and navigable flow. • Combine the three methods to calculate the comprehensive ecological water demand. • Establish three operation models considering comprehensive ecological water demand. • Quantitatively analyze the relationship between power generation and ecologic flow. • NSGA-II is employed to solve multi-objective problem. Abstract Hydropower plants operation may change river flow, thereby degrading the stability of river ecosystems. The primary purpose of this paper is to compute the comprehensive ecological water demand and establish ecological operation models to quantitatively analyze the interactions between power generation and degree of ecological flow satisfaction under different operation modes. The comprehensive ecological water demand takes the river base flow, ecological flow process and ecological water demands of fish habitat during the spawning period into account. The driest monthly streamflow under a 90% frequency method, range of variability approach and two-dimensional depth-averaged finite element model were adopted to obtain the ecological flow. In addition, to study the impacts of the ecological operation of hydropower plants on power generation, three optimal operation models including a maximum power generation model (Model-I), a minimum ecological change model (Model-II) and a multi-objective optimization operation model (Model-III), are established. In model-II, the average annual power generation of the cascade hydropower plants decreased by 10.61% compared with Model-I, and meanwhile the degree of ecological change reduced by 75.41%, which means, the reduction of power generation by 35.66 × 108 kWh could lead to a reduction of 11.4% on the degree of ecological degradation. Afterwards, the multi-objective problem of economic and ecological benefits in model-III was solved by the application of NSGA-II. Among them, scheme 3 is recommended for Model III, and its power generation and degree of ecological change are 311.69 × 108 kWh and 6.64%, respectively. In general, mutual restrictions and conflicts between power generation and ecological demand are inevitable, but they can be optimized through multi-objective ecological operation models to fetch the coordinated development of economy and ecology. [ABSTRACT FROM AUTHOR]