Analysis Of Hydrological Situation In Guanhe Basin,A Tributary Of Jinsha River

Changes in hydrological conditions are the main driving force affecting river ecosystems and functions.In order to study the changes in water and sediment regimes in the Guanhe Basin,a tributary of the Jinsha River before and after the impact of climate change and human activities,this paper selects the water and sediment data of the Doushaguan Hydrological Station in the Guanhe Basin from 1959 to2018 for a total of 60 years,and uses the Mann-Kendall trend method to analyze runoff,Inter-annual and intra-annual changes in sediment transport.Apply the Eco-hydrological Index Variation Range Method(IHA/RVA)to analyze the change degree of water and sediment single hydrological indicators from 1959to 1996(hereinafter referred to as the T_A period)and 1996 to 2018(hereinafter referred to as the T_Bperiod).Optimize the fitting of the water-sediment marginal function,construct the water-sediment joint distribution function,and analyze the flood and drought encounter.Using the double cumulative curve method,The cumulant slope change rate comparison method and the elastic coefficient method based on Budyko hypothesis explore the contribution of climate change and human activities to the change of runoff and sediment.The result shows:1)From 1959 to 2018,the annual runoff and annual precipitation in the Guanhe River Basin showed an insignificant decrease,and the annual sediment volume showed a significant downward trend;the hydrological change degree of the monthly average flow value of T_B reached 34%,and the hydrological change degree of the monthly average sediment content value reached 40.58%,both showing a moderate change.The hydrological change degree of the monthly average flow value in April was 69.37%,showing a high degree of change.The water and sediment changes during the T_A and T_B stages were more obvious in the flood season;the sediment content was the highest in July,4.23 kg/m~3 reduced to 1.85 kg/m~3.2)According to the minimum sum of square deviation criterion(RMSE)and the test results of the AIC criterion,the Weibull function is used as the marginal distribution function for the annual runoff in the T_A stage,and Pert is used as the marginal distribution function for the annual sediment concentration in the T_A stage.;Johnson SB is used as the edge distribution function for the annual runoff in the T_B stage,and the Gamma(RMSE=0.168;AIC=-33.639)is used as the edge distribution function for the annual sand content in the T_B stage.The fitting effect is the best.After fitting and optimization,the combined water-sediment distribution function of TA and TB period adopts Clayton copula function model.3)There are more water-sediment combinations with a larger probability value in the T_B stage,and the probability of the same abundance of water and sand in the T_B stage is the largest.The probabilities in the T_A and T_B stages account for 12.74%and 20.29%of the synchronization probability,respectively.The T_A stage has a variation range of 9.8%?12.74%,the T_B stage variation range is 6.52%?20.29%,It shows that climate change and human activities have increased the probability of high water-sediment level combination,and the impact on the synchronous and asynchronous frequency of water-sediment is not obvious,but it affects the stability of water-sediment flood and drought.The cumulative slope change rate method is used to calculate that the contribution rates of human activities,annual precipitation,and annual potential evaporation to the annual sediment volume are69.22%,29.66%,and 1.12%,respectively.The double cumulative curve method is used to estimate the total amount from 1996 to 2018.The amount of sediment reduction is 2564.66×10~4t,an average of116.57×10~4t per year.Human activities are the most important factor influencing sediment transport changes in the Guanhe Basin;the cumulative slope change rate method is used to calculate the impact rate of climate change on the runoff reduction in the basin is 80%.Based on the six elastic coefficient formulas assumed by Budyko,the impact of climate change on the reduction of runoff in the Guanhe River Basin is 72.97%to 81%,and climate change is the main reason for the reduction of runoff in the Guanhe River Basin.