Multi-type Change Points Detection In Hydrological Time Series In Wei River Basin

The natural environment has been changing under the influence of climate change and human activities.In the meantime,the hydrological system has changed and the hydrological time series,one of its characteristics,shows more significant nonlinearity and complexity.In the processing,human activities play an important role,which have greatly promoted regional economic growth while some unreasonable behaviors also led to many problems,such as water shortages,water pollution,lower river ecological service,the decline of water resources carrying capacity(WRCC).These problems have seriously threatened the socio-economic sustainable development.Moreover,along with the balance of the hydrological system broken,the consistency of the hydrological time series in some basins no longer exist,the statistical law in original river hydrological system could not be reproduced in the future,the entropy of the system has increased greatly,and the long-range memory in the series lose.As a result,the nonconsistency,non-stationary,multifractal properties have become the new keywords of hydrological time series.At the same time,these changes have undoubtedly sounded the alarm to the traditional hydrological design methods.A series of problems,such as how to predict the future runoff accurately and how to carry out scientific and effective regional water resources management,were suddenly put on the scientists' agenda and required to solve.However,to answer these problems,it must be known firstly how the hydrological system changes,that is,the identification and diagnosis of hydrological variations.In view of this,the thesis summed up and extended the concept and connotation of hydrological changes,classified the methods for hydrological change-point detection,and then built the comprehensive identity and diagnosis system of hydrological system variations from the perspectives of hydrological statistics,time series theory,system theory and physical cause analysis.Also,it took the Wei River basin as a case area,launched a comprehensive analysis of hydrological variations,to explore the characteristics and driving mechanism of the hydrological system variations in the Wei River basin.The main contents and conclusions are as follows:(1)Summing up and extending the research founding on the hydrological variations.This study rewrote the concept of hydrological variation and classified the existing detection methods for hydrological variations comprehensively and systematically based on the previous research results.The classification was done in term of five aspects that are respectively the attributes of hydrological series,the identify demands and forms of hydrological variation,the assumptions of detection approaches and spatial dimensions.Furthermore,this thesis discussed some problems that have existed in the process of hydrological variation diagnosis,such as skewness,seasonal trend,abnormal value,serial autocorrelation impacts,and the masking effect in change point detection,etc.And it introduced a series of treatment measures to these problems,which can effectively improve the applicability and accuracy of these test methods.(2)Comprehensive diagnosis system of hydrological variations.Most of the previous studied methods of hydrological changes were built on statistical theories.The accuracy of test result can only be checked by the significance test.Therefore,many people would often questioned the conclusion and considered it lack credibility.To this,this thesis did the identity and diagnosis from the multiple perspectives or based on many parameters,and determined the real change points of hydrological system by a comprehensive diagnosis model.The model included the following sub-modules:(1)mean change diagnostic module;(2)regression change diagnosis module;(3)variance change diagnostic module;(4)period change diagnosis module;(5)long-range autocorrelation change diagnosis module;(6)entropy change diagnosis module;(7)eco-hydrological correlation change diagnosis module;(8)sediment index change diagnosis module;(9)precipitation-runoff long-range correlation change diagnosis module;(10)spatial change diagnosis module.The integrated diagnostic system of hydrological changes can test the change of most elements or processing in the hydrological system respectively,and then synthesize all the results to obtain the real conclusion by diagnosis.In this study,it is considered that the changes of the hydrological system are true only when most of the elements are mutated at the time.(3)Comprehensive identity and diagnosis in Wei River basin.This study used the integrated diagnostic system to test hydrological variations in the Wei River basin.The module diagnostic steps are as following: the preliminary analysis of hydrological conditions,mean change diagnostic,regression change diagnosis,variance change diagnostic,period change diagnosis,long-range autocorrelation change diagnosis,entropy change diagnosis,ecohydrological system change diagnosis,sediment index change diagnosis,precipitation-runoff long-range correlation change diagnosis;and spatial change diagnosis.In the processing,the feasibility and reliability of each sub-module algorithm was verified.Then,integrating all of sub-module diagnostic results,it was obtained the real change intervals of hydrological system in Wei River basin by comprehensive diagnosis.In addition,the results show that it is necessary to jointly detect the variations of the hydrological system from multiple perspectives because the true change points may be missed if the mean change test was only applied in the hydrological system.(4)Attribution analysis to hydrological variations in Wei River basin.The thesis analyzed the relationship between the driving factors and the changes of the hydrological system through the conceptual driving model and roughly explained the driving mechanism of hydrological variation.The results presents that the changes of water intake driven by reservoirs construction,precipitation and total social water consumption were the main reason for the variations of hydrological system in Wei River basin.The changes of soil and water conservation area and land use type,resulting in a larger regional evaporation,also drove the hydrological system change of the Wei River basin in a certain extent.Form the attribution results,it was also verified the reliability of the "real" change of the hydrological system in the Wei River basin to some extent,which can provide important reference information for regional water resources management and hydrological forecasting.