Research On The Characteristics And Influencing Factors Of Runoff Of The Hulu River,A Tributary Of The Weihe River

Under the background of global climate change and human activity influence,the water cycle has taken place great changes and many parts of the world have been facing various sorts of serious water resource problems.In recent years,the Hulu River' surface water resource has been decreasing sharply,especially from the 1990 s,and the hydrologic cycle law has been changing a lot,for an example,there is little change in precipitation but runoff is decreasing obviously,which has broken the balance between supply and demand and has seriously affected the sustainable development of social economy in the Hulu River Basin.The paper studies on the annual distribution characteristics and their temporal and spatial variation characteristics of the Hulu River runoff by non-uniform coefficient(Cv),complete adjustment coefficient(Cr),concentration(RCD)and concentrated period(RCP),according average monthly runoff data of the Jingning hydrological station on the upper reaches and the Qinan hydrological stations on the downstream.Besides,the paper studies on the variation rule of the runoff,basin precipitation and evaporation,such as annual variation trend,period and mutation characters,using the method of standard departure accumulation curve method,wavelet analysis and Mann-Kendall and so on,according annual runoff data of the two main hydrological control stations,precipitation and evaporation data in the Hulu River Basin.Finally,the paper adopts double mass curve of precipitation and runoff to investigate precipitation and human activities on the Hulu River runoff change.Results show as follows:(1)The annual distribution characteristics of the Hulu River runoff: The runoff distribution mainly concentrating on the period of early June to early September and the runoff of upstream and downstream respectively making up 65.01% and 61.35% of annual runoff during the high flow period,is extremely uneven.The index of Cv,Cr,and RCD of the Jingning station runoff is greater than that of the Qinan station,which shows that the downstream runoff distribution characteristics are more stable,and the RCP of Qinan station concentration degree is slightly larger than Jingning station,which indicates that runoff concentration period of downstream is slightly behind upstream.The time variation of runoff distribution characteristics of the Hulu River Basin is not obvious.(2)The inter-annual variation law of the Hulu River runoff: The variation trend of runoff in the upstream and downstream manifests good uniformity.Both upstream and downstream runoff shows a downward trend and has declined obviously since the 1990 s.But the downstream runoff transformation is more frequent than the upstream runoff,which probably be related to larger watershed area,more tributaries,human activity influence,complex underlying surface conditions and other factors of the downstream.Finally the mutation of downstream runoff happened in 1988,but there are no obvious abrupt changes in upstream.(3)Comparison and analysis of runoff and precipitation annual variation in the Hulu River Basin: The variation trend of runoff and precipitation manifests good uniformity.Both runoff and precipitation are decreasing,however,the rate of runoff reduction is far greater than that of precipitation.From the perspective of varying period,runoff and basin precipitation change cycle year shows little corresponding relationship,and the varying cycle of runoff is longer than that of precipitation.Finally the mutation of downstream runoff happened in 1988,but there were no obvious abrupt changes in watershed precipitation.Before the 1990 s,precipitation is the main influencing factors of the Hulu River runoff.(4)Comparison and analysis of runoff and evaporation annual variation in the Hulu River Basin: The variation trend of evaporation of the upstream and downstream is different,and both the upstream and downstream evaporation declines slowly on the whole.However runoff has declined obviously since 1990 s,which shows that evaporation has little effect on runoff in the Hulu River Basin.(5)The influence of human activities on the Hulu River runoff: In 1967-1991,the rate of human activities affecting on the upstream and downstream runoff respectively accounts for 25.0% and 29.7%,and accounts for 50.8% and 60.5% in 1992-2016.The rate of human activities effect on the downstream is greater than that of the upstream,which illustrates the impact of human activities on downstream runoff is more serious.Besides,the rate of human activities effect in 1992-2016 is bigger than that in 1969-1991,which confirms that precipitation has changed little but runoff has decreased dramatically since the 1990 s in the Hulu River Basin.