Analysis On The Characteristics Of Extreme Precipitation And Joint Distribution With Flood In The Lower Reaches Of Liaohe River

Based on the daily precipitation data of five meteorological stations from 1968 to 2018 in the lower reaches of the Liaohe River and the daily flow data of two hydrological stations,construct extreme precipitation index(AM1D,AM5 D,R1mm)and annual precipitation series.The analysis and discussion of the evolution characteristics of precipitation and the two-dimensional joint distribution characteristics of extreme precipitation and flood are aimed at improving the understanding of the hydrological process of the basin,improving the flood control planning,disaster prevention and mitigation capacity of the basin and the utilization of flood resources.Use the linear regression method,trend coefficient method,R/S analysis method,M-K mutation test,sliding t test method and cumulative anomaly method to analyze the extreme precipitation trend changes,The research shows that the correlations of the four indexes with time change are relatively small.Except for the upward trend of AM1 D during the study period,the rest of the indexes are in a downward trend.In the forecast of future trends,there is an insignificant upward about AM1 D and AM5 D,while annual precipitation series and R1 mm are not decrease significantly.The mutation points are mainly concentrated around 1975,1993 and 2000.Based on the Morlet complex wavelet analysis method,the extreme precipitation cycle is analyzed from four aspects: wavelet coefficient real contour map,wavelet coefficient modulus contour map,wavelet variance graph and main period trend graph.The research shows that: The cycle scales are around 5-8 years,12-19 years and 26-31 years,but there are differences in the period of stable performance;the periodic oscillations around 17 years are the strongest and are the first main cycle;three series are all exhibited a stable cycle before 2000,and different changes occurred after 2000.Calculate the three correlation coefficients of Pearson,Kendall and Spearman,select the extreme sample pair,and perform the edge distribution fitting of the five functions of GEV,Gamma,Lognormal,Log-Logistic and P-III for extreme precipitation indicators and flood indicators,then perform the three tests of K-S,Chi-Squared,Anderson-Darling.The results show that AM7 D has the highest correlation with AM1 R,and the edge distribution can fit the index sequence well.Among them,the GEV distribution and Lognormal distribution are the optimal probability models for the extreme precipitation index and flood precipitation index,respectively.Based on the Clayton Copula,Gumbel Copula and Frank Copula functions in the two-dimensional Achimedean Copula function,the two-dimensional joint distribution of extreme precipitation and flood is constructed,and the goodness of fit evaluation is carried out through the three indicators of RMSE,AIC and BIC,and the optimal model is selected.Draw the joint probability,joint recurrence period,joint transcendental probability,co-occurrence recurrence period,conditional probability and conditional recurrence period.The results show that: Frank Copula function is the function model for constructing the optimal distribution;with the increase of the AM7 D and AM1 R indicators in the lower reaches of the Liaohe River,the joint recurrence period is 10 times or even 50 times higher than the current recurrence period,indicating that both indicators greater than or equal to a specific value of the interval between occurrences is extremely long,and the probability of occurrence is extremely small.It can be speculated that the hydrological response of flood to precipitation requires a certain time and is delayed;given the specific value of AM7 D,the conditional probability of AM1 R occurrence varies As AM7 D increases,the condition recurrence period decreases.In a nutshell,the larger the precipitation index value,the greater the possibility of flooding.