Trends of streamflow, sediment load and their dynamic relation for the catchments in the middle reaches of the Yellow River over the past five decades

摘要

To control severe soil erosion on the Loess Plateau, China, a great numberof soil conservation measures have been implemented since 1950s andsubsequently, the "Grain for Green" project was implemented in1999. The measures and the project resulted in a large scale land use/coverchange (LUCC). Understanding the impacts of the measures and the project onstreamflow, sediment load and their dynamic relation is essential because thethree elements are closely related to the sustainable catchment managementstrategy on the Loess Plateau. The data for seven selected catchments in themiddle reaches of the Yellow River were used and standardized with theprecipitation and the controlling area for analysis. The nonparametricMann-Kendall test and the Pettitt test were employed to detect trends and changepoints of the annual streamflow and annual sediment load. Simple linearregressions for the monthly streamflow and sediment load from May to Octoberwere made to express their relationship. Based on the change pointidentification and the time when the project began to be implemented on the LoessPlateau, the complete time for the data records was divided into three periodsto compare the change degrees of streamflow, sediment load and theirrelation for the catchments.Results show that there are three types of responses in streamflow, sedimentload, and their dynamic relations for the seven catchments. The effects ofthe LUCC on streamflow, sediment load, and their relationships are greatestin the three transition zone catchments followed by the two rocky mountaincatchments. The effects are much weaker in the two loesshilly-gully catchments. In general, the change degrees for sediment load aremuch greater than those for streamflow, which results from the decreasedstreamflow and weakening trend of their dynamic relation period by period incatchments.