Analysis On Joint Operation Of Inter-Basin Water Diversion And Reservoir Water Supply And Impacts Of Change Conditions On It

Water transfer projects have been promoted as a real option to relieve regional water supply pressures caused by the non-uniform temporal and spatial distributions of water resources. It’s necessary to design and optimize a set of water diversion-supply rules in order to improve the water diversion efficiency and effectiveness. Besides, it will be a long term operation after the project constructed. The changing climate condition and human activities may have impact on future reservoir operation. The future climate and human activities forecast and the impact of them attracts researchers’attentions. It is critically important to understand the performance of the historical optimal water diversion rules in changing future conditions, which might affect the water resources available in the receiving regions. Regarding this as the entry-point, this paper aims to develop an assessment framework to study the impacts of climate change and human activities on optimal water diversion strategies of a receiving reservoir in the water diversion project. The proposed framework is demonstrated using the water transfer project in the water deficit Biliu River reservoir basin, China. The main research content and results of this paper are summarized as follows:(1) Analyze the historical precipitation and runoff variation, including the characteristic and change trend. On the basis of the variation analysis results, identify the impact of climate change and human activities qualitatively, as well as the actual water diversion problems in the study area. The analysis and problem identification laid the foundation for the following exploratory researches, i.e. optimize a Pareto front of inter-basin water diversion and reservoir water supply joint operation rules, as well as the impacts of future climate changes and human activities on reservoir future operation.(2) Developing inter-basin water diversion and reservoir water supply joint operation rules of the receiving reservoir based on the thought of adding water diversion rules. The optimal water diversion problem is defined as a multi-objective problem with two conflicting objectives:minimizing the public and ecological water supply shortages. The popular non-dominated sorting genetic algorithm II (NSGA-II) is used to solve the optimization problem with two ecological water supply cases, i.e. the "good" and’"medium" cases. The derived Pareto-optimal solutions based on historical runoff series, hereinafter referred to as the historical optimal rules for short. The historical optimal rules are demonstrated reasonable according to the characteristic of joint operation rules, as well as the reservoir operation processes. Compared to the optimal results of no water diversion conditions, the designed and optimized operation rules are demonstrated can increase290X106m3water supply to the public water user when divert250×106m3water, and satisfy the guarantee rate of all the users. It implies that the optimal joint operation rules play a significant role to safeguard regional economic.(3) Based on the distributed hydrologic model SWAT, the hydrologic response of future climate change and human activities are analyzed. On the one hand, three climate models (ACCESS1.0, BCC-CSM1.1(m) and CMCC-CM) of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) respectively run for a high Representative Concentration Pathway (RCP8.5) are selected. And a modified Morphing method is used to downscale the precipitation and temperature data. On the other hand, aim to solve the challenge of human water consumption forecast, which is one of the three main human activities, this paper put forward the Fuzzy Inference Model of human water consumption based on the precipitation levels of adjacent years. The efficiency of the fuzzy interface model is demonstrated based on the historical human water consumption data. The fitting degree and simulation evaluation indexes of the runoff simulation results modified by considering human water consumption are much better than the SWAT simulation results. The parameters of fuzzy rules, derived by the Fuzzy Inference Model, reveal the historical rules of the relationship between the human water consumption and the precipitation levels of adjacent years.Because there’s no population growth plan in the study area, the inference model and the derived historical parameters of fuzzy rules can be an important basis for forecasting the future human water consumption.(4) Drive SWAT model with several future climate scenarios, directly considering Yushi reservoir in the model, in order to generate future runoff conditions.In addition, modify the SWAT simulation results based on the Fuzzy Inference Model of human water consumption. Results show that, under future climate models ACCESS1.0, BCC-CSM1.1(m) and CMCC-CM, the future runoff increase20.55%, decrease9.59%and decrease29.13%respectively, compared to the historical runoff series. Statistical approaches are used to analyze the changes of the characteristic values, distribution and change trend of future precipitation and runoff series. The results of future runoff changes are the base of the analysis of the change conditions impact on reservoir joint operation rules.(5) The future runoff sharp decreased scenario (CMCC-CM model), probably can’t guarantee water supply to all the water users. According to the mentioned scenario, the performances of the historical optimal rules are re-evaluated under the "good" and "median" ecological water supply cases, using the predicted future runoff by comparing several operation indicators such as the average annual amount of water supply, the guarantee rate of water users, etc. In addition, the joint operation rules are re-optimized under future runoff when the main operation indicators appear worse. Results show that, under the mentioned scenario, when consider "median" ecological water supply, re-optimizing the joint operation rules can guarantee water supply; while consider "good" ecological water supply, reducing the public water supply target to457×106m3(51×106m3less than the original public water supply target), is inevitable in order to guarantee water supply for all the three users.(6) Uncertainties of future climate scenarios impacts on joint operation are further analyzed. Besides the selected three CMIP5climate models, assumption of climate variables variation scenarios are also used to evaluated their impacts on the joint operation. The three assumptions of climate scenarios results in future runoff decrease9.91%,15.08%and21.35%respectively. The critical conditions of adjusting the historical optimal rules are identified based on the mentioned scenarios. According to the comparison of their performances using the historical optimal rules, suggestions are made finally:when the amount decrease of future runoff is less than15%, the historical optimal rules still can be used and the guarantee rate of water users can be basicly satisfied; while the amount decrease of future runoff is larger than15%,"median" ecological water supply case is suggested to be considered, or properly reducing the public water supply target of "good" ecological water supply case is inevitable, in order to guarantee water supply.