Study On Drought Evolution And Adaptive Reservoir Operation In A Changing Environment

Climate change and human activities have posed new challenges to water resource management.On the one hand,the hydrological assumption no longer holds.The mean and extreme values of hydrological variables have significantly changed in most parts of the world.On the other hand,with the continuous increase in socioeconomic development,the water demands assigned to hydraulic structures are also shifting dynamically.Reservoirs are the main constructions those regulate water resources.Under the circumstance of non-stationarity,conventional reservoir operation is no longer adequate to conquer the future hydrological conditions and meet human water needs.Therefore,adaptive reservoir operation under changing environment has become an essential issue.This thesis starts with the situation of extreme hydrological events through analyzing the impact of climate change and human activities on future global droughts.In order to handle the intensified future droughts,an adaptive reservoir refill operation model is developed using the hedging theory.Then the hedging based theoretical analysis of traditional reservoir rule curves design proves the consistency of the hedging theory and conventional rule curves.Based on this connection,the conventional rule curves adaptation strategy is future analyzed.The main research contents and results of this dissertation are as follows:(1)Analyzed the evolution of global drought and the frequency of extreme droughts in the future.An integrated analysis of climate change and human influence on meteorological drought,agricultural drought and hydrological drought at global scale and the interconnection between them is conducted.This analysis is based on multi-model experiments consisting of 20 GCM-GHM model combinations.Results show that the impact of climate change on extreme drought frequency is greater than that of human activities.The extreme hydrological droughts are likely to occur significantly more frequent between latitude 25°N-40°N and 15°S-50°S.(2)Developed an optimal hedging rule for reservoir refill operation.Based on the inflow forecast uncertainty,the probability distribution of the maximum refill water availability at the end of refill season is derived.The water conservation benefit and flood damage loss are formulated according to the refill possible cases.The two stage hedging based refill optimization model is constructed.Then the optimal refill operation criteria and a refill hedging rule curve are derived.The Danjiangkou reservoir case shows that the refill hedging rule performs better than the current rule curves and leads to a gradual dynamic refilling based on forecast information.(3)Proved the theoretical consistency of conventional rule curves and hedging optimization.With focuses on the three basic problems surrounding the design of conventional rule curves,namely the law and design of water supply rule curves,the determination of flood storage,the division of refill and drawdown circle,the connection between rule curves and hedging theory is provided.Both the theoretical analysis and the Danjiangkou reservoir case study reveal that behind conventional rule curves lies the hedging theory,suggesting the consistency between the two.Under the historical streamflow conditions,the hedging based rule curves will be close to the conventional ones.On this basis,further analysis of rule curves based adaptive adjustment strategy is carried out using the hedging theory.