1956—2017年黄河上游水沙变化及其驱动因素

Variation of runoff and sediment load and their driving factors on the upper stream of the Yellow River from 1956 to 2017

为明确黄河上游径流输沙时空变化及其驱动因素,采用Mann-Kendall趋势检验、BFAST检验、水沙关系曲线以及双累积曲线等方法,分析黄河上游兰州断面以上4个水文站1956—2017年径流输沙变化及其驱动因素。研究表明:黄河上游唐乃亥站的年径流输沙呈非显著减少趋势,贵德、循化和兰州站的年径流输沙均呈显著下降趋势,且径流输沙的减少量沿程增加,趋势更为显著。黄河上游水沙变化的突变年份发生在1968和1986年,佐证了上游大型水利工程的显著调控影响。河流径流量变化较为平缓,最大减幅为20%;输沙量变化较为强烈,1987—2017年贵德、循化和兰州站减幅均>70%。不同时段的水沙关系曲线表明,黄河上游各站点水沙关系于1986年后发生显著改变,河道输沙特性发生明显变化,河道输沙量明显减少。不同时段内人类活动对输沙量减少的贡献率均>98%,对径流量减少的贡献均>63%。结果表明:人类活动是黄河上游水沙变化的主要驱动因素,大规模的水土保持措施与水利工程能够有效拦蓄泥沙,调控径流、输沙关系。

[Background]Rivers are the primary agent to provide water resources for sustaining regional economy and society development,and conveyor belts between land and ocean which transports large amount of sediment and nutrients to the oceans.The runoff and sediment load in the Yellow River basin have been dramatically altered by climate change,vegetation restoration,soil and water conservation measures and hydraulic projects during the past decades.Thus,assessing the spatial-temporal variation in runoff and sediment load and their relationship in the upper stream of the Yellow River is desirable,and may provide valuable insights of watershed management and soil and water conservation.[Methods]In this study,the Mann-Kendall test,Sen's slope estimation,and BFAST model were employed to investigate the temporal trends and abrupt changes of the annual runoff and sediment load at 4 hydrological stations(including Tangnaihai,Guide,Xunhua and Lanzhou stations)in the upper stream of the Yellow River from 1956 to 2017.Then the sediment rating curves were applied to analyze the relationship of flow-sediment during different periods,and double mass curves were used to separate the impacts of climate change and human activities on the mean discharge changes and to quantify the drivers of variation of runoff and sediment load.[Results]The annual runoff and sediment load presented decreasing trends from 1956 to 2017 at 4 stations,and decreasing trend in the most stations was significant(P<0.05)except Tangnaihai station.The most dramatic decrease in annual sediment load was observed at Xunhua station.Annual average sediment load at Xunhua station in 2010—2017 accounted for 4%of that in 1956—1968.Abrupt changing points of annual runoff and sediment load occurred in 1968 and 1986,confirming the significant alternation effects of large hydraulic projects.The variation in annual runoff was more moderate,with a maximum reduction of 20%.Compared with annual runoff,annual sediment load showed extraordinarily significant reduction of 70%at Guide,Xunhua and Lanzhou stations from 1987 to 2017.The relationship between monthly runoff and sediment load in the upper stream of the Yellow River changed significantly since 1986,with significant changes in the sediment load capacity and significant reduction in the amount of sediment load.In different periods,human activities contributed>63%and>98%to the reduction of runoff and sediment load,respectively.[Conclusions]Human activities are the main driving factor of variation of runoff and sediment load in the upper reaches of the Yellow River basin.This indicates that large-scale soil and water conservation measures and hydraulic projects may effectively trap upstream incoming sediment and regulate the relationship between runoff and sediment load.