| Due to low vegetation coverage,climate and other factors,serious soil erosion,large sediment content,and fragile ecological environment,serious soil erosion and large sediment content in the upper reaches of the Wei River,it is a fragile ecological environment,climate change,human activities and water conservancy projects have a large impact on hydrological elements,and the non-uniform characteristics of hydrological sequences appear,and the traditional hydrological frequency analysis methods can no longer meet the needs of hydrological non-consistency analysis.Therefore,it is of great practical significance to carry out the characteristic analysis of hydrological elements in the basin and to study the nonuniform distribution fitting of hydrological elements.In this paper,the precipitation,runoff and sediment sequences of Wushan,Gangu,Qin’an,Tianshui and Beidao in the upper reaches of the Weihe River were taken as the research objects,and the evolution of hydrological elements in the area was analyzed statistically.On this basis,the distribution of precipitation,runoff and sediment sequences was non-uniformly fitted by GAMLSS model,which was aimed at better paving the way for hydrological analysis and calculation in the river basin,and improving the flood control safety and efficient use of water resources in the study area.The main research contents and achievements are as follows:(1)The linear regression method,Mann-Kendall and Spearman method were used to analyze the trend characteristics of precipitation,runoff and sediment sequence.The results show that the change trend of precipitation and runoff is basically the same,showing a nonsignificant increase trend,while the amount of sand transport shows a significant downward trend,which may be closely related to the water conservancy projects in the river basin and the regulation of the ecological landscape along the river basin.Mann-Kendall,cumulative distance method,ordered clustering method and heuristic segmentation method were used to analyze the mutations of precipitation,runoff and sediment sequences,and found that the precipitation of five stations in Tianshui Survey Area,Wushan,Gangu,Qin’an,Tianshui and North Dao,had mutations in 2002 and 2017,runoff mutations in 2012 and 2017,and sediment mutations around1994 and 2003.(2)Wavelet analysis was used to determine the cycle of precipitation,runoff and sediment sequences.The results show that the distance between Wushan-Beidao in the upper reaches of the Weihe River is more than 100 kilometers,and the cycle difference is not large,and there are the first main cycle and the second main cycle of precipitation,runoff and sand transport at each station,which are manifested as the first main cycle of about 22 years and the second main cycle of about 11 years,which are closely related to sunspot activity.In addition to the first main cycle of about 22 years,there is a second main cycle of about 6 years.(3)The GAMLSS model was used to select different distribution functions,and time covariates were established to perform consistent and inconsistent fitting of precipitation,runoff and sand transport in the upper reaches of the Wei River,and the model fitting evaluation was carried out by comparative analysis of AIC criterion and SBC criterion,and non-consistent model fitting was performed for precipitation,runoff and sediment sequences.The results showed that under different distribution conditions,the optimal distribution models of precipitation were Lognomal,Normal,Lognomal,Lognomal and Lognomal in the five hydrological stations of Wushan,Gangu,Qin’an,Tianshui and Beidao.The optimal distribution model of runoff was Lognomal,Gamma,Lognomal,Wei,Lognomal.The optimal sediment distribution models were lognomal,Wei,Gamma,Lognomal,and Lognomal.(4)The smallest model of AIC and SBC was selected as the optimal model,the normal QQ plot and worm plot were used for residual discrimination,and the Filliben correlation coefficient test with a significance level of 5% was carried out for goodness-of-fit evaluation,and the position parameters and scale parameters were calculated,and the non-uniform distribution fit of five hydrological stations in Wushan,Gangu,Qin’an,Tianshui and Beidao was tested.The results showed that the residual points of precipitation sequences,runoff sequences and sediment sequences in the five stations of Wushan-North Road were all located between the upper and lower elliptical curves after fitting by the GAMLSS model,satisfying95% confidence.The residual points in the five normal Q-Q stations were distributed around the 1:1 straight line,and the Filliben correlation coefficient was close to the 1 model,which further tested the rationality of the model and provided a basis for non-uniform hydrological analysis of the river basin.(5)Considering that the covariate is constant,time t is the covariate,and time t,precipitation and temperature are covariates,the runoff sequence is fitted to a non-consistent model to obtain the optimal model,the optimal distribution model is lognomal,Gamma,Lognomal,Lognomal,Lognomal,and the values of AIC and SBC for nonlinear fitting of runoff sequences are further found,Wushan Station,Qin’an Station,Tianshui Station,and Beidao Station are small as a whole,and Gangu Station is larger as a whole.The overall fitting effect was slightly better than that of a single time t for the covariate fitting result. |
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