Analysis Of Baseflow Evolution Characteristics And Its Influencing Factors In Chengbi River Basin

Under the combined action of global climate change and human activities,the relationship between the supply and demand of water resources in Chengbi River Basin is becoming increasingly tense.As an important part of river basin water resources,the baseflow is an important indicator of river basin ecological health.Studying the baseflow evolution characteristics and influencing factors will help to understand the characteristics of water resources and provide a scientific basis for sustainable utilization of water resources and ecological environment protection.Based on this,this thesis selected the Chengbi River Basin as the research object to study the characteristics of baseflow evolution and its influencing factors.The main contents and results are as follows:(1)Based on the daily runoff data of Chengbi River Basin from 1963 to2019,the applicability of 10 baseflow segmentation methods,such as the fixed interval method,smooth minimum method and Lyne-Hollick digital filtering method,was verified by the stability of the baseflow index,the rationality of baseflow process line and the reliability of annual baseflow.The results showed that the baseflow estimated by the Boughton-Chapman digital filtering method with a filtering parameter of 0.95 and a filtering number of 3 times has good stability,high reliability and best applicability.(2)The Kendall rank correlation method,Mann-Kendall mutation trend test method and Morlet wavelet analysis method were used to analyze the interannual evolution characteristics of the baseflow in the Chengbi River Basin,and the uneven distribution coefficient,concentration degree and concentration period were introduced to analyze the annual distribution characteristics of the baseflow.The results showed that the annual baseflow of the basin showed an insignificant decreasing trend and no variation occurs.The first main cycle is18 a.The annual distribution of baseflow in the basin showed a unimodal distribution,and the baseflow in summer and autumn accounted for 68.15% and21.37% of the annual baseflow,respectively.The baseflow changes greatly during the year,and the concentration period is mainly in July.The distribution of the year was extremely uneven,and the unevenness gradually increases with time.(3)The variation characteristics of meteorological elements in the basin were analyzed,and the influence of climate change on baseflow was qualitatively studied.The results showed that the annual potential evapotranspiration showed a significant decrease trend,and the annual precipitation and average temperature showed an increasing trend,among which the annual average temperature showed a significant change trend.The annual variation of precipitation,average temperature and potential evapotranspiration showed unimodal or bimodal distribution.Precipitation is the main influencing factor of baseflow change,which is positively correlated with baseflow.Temperature and potential evapotranspiration have relatively a small influence on baseflow change.(4)The contribution rate of climate change and human activities to baseflow change was quantitatively analyzed by the double cumulative curve method and cumulative slope change rate comparison method.The results showed that the period from 1963 to 2019 can be divided into the base period(T1)and the influence period(T2～T4)bounded by 1979,1993 and 1999.Considering the influence of precipitation,temperature and potential evapotranspiration,the contribution rates of climate change to baseflow in T2,T3 and T4 are 4.79%,64.80% and-16.17% respectively,and the contribution rates of human activities to baseflow are 95.21%,35.20% and 116.17% respectively.The climate change in T3 is the main cause of baseflow change.Human activities in T2 and T4 are the main drivers of baseflow changes.