Non-stationary Analysis Of Runoff Series In The Upper Reaches Of Fenhe River

Runoff reflects the abundance of water resources in a region.Accurate frequency analysis and calculation is the basis of reasonable planning,design,construction and normal operation management of water conservancy projects.However,under the influence of climate and various human activities,the natural environment is always in a state of constant change,among which the hydrological system has also changed significantly,resulting in varying degrees of variation in the runoff series,which no longer meets the independent and identical distribution,that is,there is inconsistency in the runoff series.If we calculate the frequency of inconsistent hydrological series directly according to the traditional method,it will make water conservancy projects and flood control and drought relief measures face unpredictable risks,lead to huge economic losses,and even threaten the safety of human life.Therefore,how to reasonably analyze and calculate the frequency of inconsistent runoff is particularly important.In this paper,the runoff data of four stations(Shangjingyou station,Fenhe Reservoir station,Zhaishang station and Lancun station)in the upper reaches of Fenhe River from 1958 to 2000 are taken as the research object for analysis and research.After the preliminary analysis of their statistical characteristics and variation characteristics,the inconsistency diagnosis is carried out.The preliminary diagnosis uses the process line method and sliding window Kolmogorov-Smirnov(K-S)test,and Extreme-point symmetric mode decomposition(ESMD)was used for trend and jump diagnosis,combined ESMD with Sliding period identification method based on correlation coefficient(SRPT method)is used for period analysis.It is expected that a single method can be used to study the inconsistency of hydrological series from three aspects of trend,jump and period.SRPT method is used to study the inconsistency of annual rainfall runoff series and monthly,dry season and flood season runoff series in the upper reaches of Fenhe River to explore the influencing factors of the inconsistency.Calculates the frequency of inconsistent annual runoff series of each hydrological station by using the frequency calculation methods of inconsistent hydrological series based on Ensemble Empirical Mode Decomposition(EEMD decomposition)and ESMD decomposition respectively,so as to provide reference for the planning and management of water conservancy projects in this area and provide the basis for design,management and operation.The main contents and results are as follows:(1)The analysis of intra-annual runoff variation show that there is a similar trend in the runoff series of each hydrological station.The C_v,CI and Gini coefficient are used to analyze the intra-annual non-uniformity.The C_vof intra-annual runoff in each hydrological station is in the range of[0.2,1.76],and the C_vshowed an upward trend during 1958?1960 and 1976?1979 and so on,which indicated that the intra-annual non-uniformity of runoff in these periods increased.CI and Gini show that there is basically the same change trend in each hydrological station.The CI values of each hydrological station are mainly concentrated in 10?20,which indicates that the annual distribution of runoff in each hydrological station presents seasonal variation and obvious non-uniformity.Gini coefficient gradually increases in the years greater than 0.5 after the 1990s,which indicates that the intra-annual distribution non-uniformity increases after the 1990s.Based on the annual runoff variation curve and annual runoff cumulative anomaly curve,it is found that the annual runoff of each hydrological station presents a downward trend year by year.The annual extreme value ratio P and the deviation coefficient C_vare used to study the non-uniformity of annual runoff.According to the order of Shangjingyou station,Fenhe reservoir station,Zhaishang station and Lancun station,the P is 37.9,19.7,33.1 and 47.5 in turn,and the C_vis 0.63,0.53,0.58 and 0.60 in turn,indicating that the annual runoff distribution of each hydrological station is significantly nonuniform.(2)The preliminary diagnosis and identification results show that the annual runoff series of the other three stations,except the Shangjingyou hydrological station,have great changes around the 1970s.ESMD trend diagnosis results show that the annual runoff series of the four hydrological stations in the upper reaches of Fenhe River have a downward trend,in which the Shangjingyou station has no significant downward trend,and the other three stations have a significant downward trend;The results of ESMD mutation diagnosis showed that the mutation point of the Shangjingyou hydrological station was in 1983,and the other three stations were in1970;ESMD combined with SRPT showed that there was periodic variation in all stations,and the degree of variation was moderate.Through comparison and practical analysis,the results show that it is feasible to use ESMD diagnosis method to analyze trend,mutation and cycle simultaneously.(3)After the preliminary and detailed diagnosis of the inconsistency of the annual runoff series of each station,it is found that the annual runoff series of each hydrological station are inconsistent,but not all the monthly runoff series of each hydrological station are inconsistent.Too large or too small runoff can reduce the impact of global climate change and high-intensity human activities to a certain extent,So that the diagnosis can not detect the variation.Based on the analysis of the inconsistency of the annual rainfall and runoff series of each hydrological station in the upper reaches of Fenhe River,it is concluded that the construction of Fenhe Reservoir may be the main factor leading to the inconsistency of the regional hydrological series in the upper reaches of Fenhe River.(4)After using EEMD method to modify the annual runoff series of each hydrological station,the design values obtained by frequency calculation according to the sequence of Shangjingyou station,Zhaishang station,Fenhe Reservoir station and Lancun station are about 18%,6%,11%and 4%less than the unmodified design values respectively;After using ESMD method to modify the annual runoff series of each hydrological station,the frequency calculation according to the sequence of Shangjingyou station,Zhaishang station,Fenhe Reservoir station and Lancun station compared with the uncorrected design values,the design values are respectively 15%,20%,5%and 19%smaller.Besides,by comparing the differences between the two methods,it is concluded that the calculation method of inconsistent runoff frequency based on ESMD decomposition is superior to the analysis method of inconsistent runoff frequency based on EEMD decomposition in both the difficulty of implementation and the final results.