Change Characteristics And Attribution Analysis Of Baseflow In The Upstream Of Zhang River Basin

With the contradiction between water resources supply and demand becoming more and more prominent in the upstream of the Zhang River basin,study on the change characteristics of baseflow plays an important role in determining runoff generation mode in a watershed,water resources redistribution and economic layout optimization.In this paper,seven hydrologic stations(Caijiazhuang,Liujiazhuang,Kuangmenkou,Shizhandao,Shiliang,Tianqiaoduan and Guantai)were selected in the upstream of the Zhang River,and their sub-basins were divided by Arc GIS.Then,taking Guantai station as an example,eight baseflow separation methods including HYSEP,BFI,Kalening and Digital Filtering methods were used to segment the daily runoff from1959 to 1990 and from 2006 to 2018.The best method suitable for the separation of the upstream of the Zhang River basin was selected.Based on the statistical analysis of baseflow separation results,the trend and mutation of baseflow at different time scales(annual,seasonal and monthly)were tested by Mann-Kendall method.Combined with the trend analysis and break point test results of areal rainfall,the change of baseflow was attributed by using Double Cumulative Curve method.The main conclusions are as follows:(1)The results of daily runoff partitioning by eight baseflow separation methods at Guantai station showed that the two-parameter Digital Filtering method(DF2)was the best,and its Nash-Sutcliffe efficiency coefficient and mean relative error were 0.86 and 7%,respectively.The baseflow hydrograph obtained by DF2 method in wet,normal and dry years were more stable,and their fluctuation changes were consistent with runoff hydrograph,which accords with the characteristics of hysteresis and depletion of runoff in the basin.Combined with the depletion curve equation,the regression constant of runoff hydrograph of seven hydrological stations in the upstream of the Zhang River basin was slightly different,and its value ranged from 0.96 to 0.99.(2)The annual,seasonal and monthly baseflow obtained by DF2 separation were relatively stable.In the upstream of the Zhang River basin,the average annual baseflow was 36.6mm,and the variation coefficient of the annual baseflow was 0.67.In the upstream of the Zhang River basin,the average seasonal baseflow was 9.42 mm,and the variation coefficient of seasonal baseflow was 1.03.The mean monthly baseflow was 2.7mm,and the variation coefficient of monthly baseflow in the upstream of the Zhang River basin was 1.09.(3)Statistical results of BFI at different time scales obtained by DF2 method showed that the average contribution rate of annual,seasonal and monthly baseflow to runoff in the upstream of Zhang River was more than 60%.In contrast,monthly BFI had the greatest variation with a coefficient of 0.27.The coefficient of variation of BFI was 0.11.The seasonal variation of BFI was the lowest,and the coefficient of variation was 0.02.(4)Both annual baseflow and BFI showed a downward trend.In the upstream of the Zhang River,the mutation years of baseflow in Caijiazhuang,Liujiazhuang and Guantai were around 1970,and the mutation years of baseflow in Kuangmenkou,Shizhandao,Shiliang and Tianqiaoduan were around 1980.The annual BFI of the Shizhandao and Shiliang changed in 1962,while the abrupt change of annual BFI at Tianqiaoduan and Guantai occurred in 1966.(5)The seasonal baseflow and BFI showed different downward trends.Among them,the mutation year of Caijiazhuang and Guantai was around 1970,the mutation year of Liujiazhuang and Shiliang was around 1975,the mutation year of Kuangmenkou and Shizhandao was around 1985,and the Tianqiaoduan was around1980.Seasonal BFI showed different downward trends.The mutation year of Caijiazhuang and Guantai was around 1970,while the seasonal BFI of Kuangmenkou and Shizhandao decreased significantly only in spring,while Liujiazhuang,Shiliang and Tianqiaoduan were relatively stable.(6)The trend and mutation point of monthly baseflow and BFI were inconsistent.The monthly baseflow and BFI in the Qingzhang River showed an upward trend compared with the Zhuozhang River and the main stream of the Zhang River.The mutation of monthly baseflow occured during 1970-1980,and the mutation of monthly BFI occured in 1959-1972.The monthly baseflow of the Zhuozhang River indicated a significant downward trend and the mutation year was around 1980,while the monthly BFI also showed a significant trend and the mutation years were not consistent.The monthly baseflow and BFI in the main stream showed no significant decreasing trend,and the mutation years were different.(7)The response of baseflow to precipitation and human activities in the upstream of the Zhang River basin was analyzed by using Double Cumulative Curve method.The results manifested that precipitation had a positive contribution rate to the reduction of baseflow,with an average value of 102.32%.The contribution rate of human activities to the reduction of baseflow was negative,and the average contribution rate was -2.46%.