Baseflow Separation And Driving Factors Of Baseflow Evolution In Typical Watershed Of Loess Plateau

With the intensification of human activities and the change of natural environment,the runoff of the Yellow River Basin has been decreasing continuously since the 1990s,which has attracted wide attention.Baseflow is an important part of the Yellow River water resources.The analysis of baseflow can help to understand the characteristics of the Yellow River water resources.It is of great significance for the ecological civilization construction of the Loess Plateau,ecological protection and high-quality development of the Yellow River Basin to study the baseflow separation and driving factors of the baseflow evolution.This study was supported by the National Key Research and Development Program of China(2016YFC040240203)and the National Natural Science Foundation of China(51979250).The Zuli River,Kuye River,Tuwei River and Jingle basin of the Loess Plateau were selected as the study areas.Based on the daily runoff data measured at the hydrological stations of Jingyuan,Wenjiachuan,Gaojiachuan and Jingle,two kinds of baseflow separation methods were used to estimate the baseflow.The baseflow process line,baseflow index and the effectiveness of baseflow segmentation were analyzed,and the appropriate baseflow separation method was obtained.The intra-annual distribution and inter-annual evolution characteristics were studied,and the driving factors of baseflow evolution were analyzed in combination with precipitation,temperature,NDVI and soil and water conservation measures.The main conclusions are as follows:(1)Appropriate baseflow separation method was studied for typical watershedsConsidering the baseflow process line,baseflow index and its eigenvalue,the effectiveness of annual baseflow obtained by different separation methods,the Chapman filter,Chapman-Maxwell filter and Eckhardt filter are considered qualitatively and quantitatively to be the more suitable baseflow separation methods for typical watersheds.The Eckhardt filter method is recommended for baseflow separation in typical watersheds of the Loess Plateau based on the typical flood process.(2)Intra-annual distribution and inter-annual evolution of baseflow in typical basins were identifiedThe annual variation of baseflow and baseflow index in typical basins becomes more stable,the coefficient of inhomogeneity and complete regulation of the baseflow decreases,and the concentration of baseflow decreases.The baseflow and runoff showed a decreasing trend,while baseflow index showed a certain increasing trend.The average annual baseflow of Zuli River,Kuye River,Tuwei River and Jingle basin was 0.39×108m3,2.40×108m3,1.73×10m3 and 1.28×108m3,respectively;the average baseflow index over the years was 0.37,0.42,0.49 and 0.48.(3)Change characteristics of runoff,climate and underlying surface in typical watersheds were analyzedThe annual runoff showed a downward trend,the temperature showed an upward trend(about 0.03℃/a).The downward trend of the precipitation in July-October was much higher than that in May-June,leading to a downward trend of the annual precipitation(1.3-1.4 mm/a in the basin outside Jingle and 0.43 mm/a in Jingle basin).The ND VI of typical basins increased significantly from July to October,and increased significantly from 1981 to 2014.The annual mean temperature of Zuli River,Kuye River,Tuwei River and Jingle basin changed abruptly in 1994,1995,1996 and 1993,and the cumulative precipitation changed abruptly in 1995,1997,1995 and 1978,respectively.The NDVI mutation point was mostly in 2001.(4)Driving factors of baseflow evolution in typical basins were revealedPrecipitation is the main meteorological factor affecting the change of baseflow.The baseflow in Zuli River and Jingle River Basin is greatly affected by precipitation in spring and summer,while the baseflow in Kuye River and Tuwei River Basin is greatly affected by precipitation in summer.When the influence of precipitation and air temperature on the baseflow weakened,the influence of human factors on the underlying surface enhanced and the influence on the baseflow increased.Precipitation and soil and water conservation measures are the main influencing factors in Zuli River Basin.Coal mining and soil and water conservation measures are the main influencing factors in Kuye River Basin,while precipitation and water conservancy projects are the secondary influencing factors.Coal mining and soil and water conservation measures are the main influencing factors in the Buwei River Basin.Precipitation and soil and water conservation measures are the main influencing factors in Jingle Basin.