| In recent decades,under the influence of climate change and human activities,great changes have taken place in the runoff and sediment load of major rivers in China.Therefore,it is necessary to study the characteristics of river runoff and sediment load changes under changing environment,quantify the contributions of the main driving factors,and deeply understand the mechanism of hydrological process under strong human interference,so as to provide scientific and technological support for comprehensive watershed management and water conservancy project construction.In this study,the runoff and sediment load data of main hydrological stations in the trunk and tributaries of major rivers in China from 1956 to 2019 were collected.The Mann-Kendall trend test,Sen slope estimation,Pettitt mutation test and other mathematical statistical methods were used to analyze the trend and mutation characteristics of runoff and sediment load series.The effects of climate change and human activities on runoff and sediment load were quantitatively evaluated by using the Double Accumulation Curve method.At the same time,combined with the data of climate,water conservancy construction,vegetation and soil and water conservation measures,the changes of climate change,reservoir dam engineering and vegetation index were analyzed to reveal their effects on runoff and sediment load changes.The main conclusions are as follows:(1)There is a significant difference in runoff variation between main rivers and tributaries in China,and sediment load generally shows a decreasing trend.The runoff of the Songhua River,Liao River and Yellow River in the north showed a significant decrease trend,while the runoff of the Yangtze River,the Pearl River and the southeastern river in the south showed no significant change,and the runoff of the Heihe River showed an increasing trend.The sediment load of Liaohe River,Haihe River and Yellow River decreased by more than90%from 1956 to 1969.(2)The abrupt change years of runoff and sediment load of major rivers in China were mostly concentrated in the 1980s and 1990s,but there were significant differences among rivers.Most rivers in the north had significant abrupt change,while those in the south had insignificant abrupt change.The abrupt change years of sediment load in different rivers are concentrated,and it has high consistency with the construction of large-scale water conservancy projects and the implementation of large-scale soil and water conservation measures.(3)There was no significant change in the amount of runoff flowing into the sea,and the amount of sediment load flowing into the sea decreased significantly.The runoff flow into the sea mainly comes from the Yangtze River,the Pearl River and the southeastern rivers,accounting for 93.06%of the total runoff flow into the sea.The annual sediment load inflow decreased from 1 809.62×10~6 t/a in the 1960s to 284.52×10~6 t/a in the last decade,a decrease of 84.28%.The Yellow River,Yangtze River and Pearl River have the highest sediment load inflow,accounting for more than 95%of the total sediment load inflow.(4)Human activities are the dominant driving factors of runoff and sediment load in major rivers in China.70.77%of the runoff changes were dominated by human activities,and the contribution rate of human activities to the runoff changes of hydrographic stations in the main and tributaries of the Yellow River was higher than 70%.29.23%of the runoff changes were dominated by precipitation,mainly distributed in the northwest basin,southwest basin and southeast basin.84.62%of the sediment load changes were dominated by human activities,and the contribution of human activities to the sediment load change is higher than 80%in the Yellow River and Yangtze River.Sediment load in 15.38%of the basin was dominated by precipitation,mainly distributed in Songhua River basin,Northwest basin,southwest basin and southeast basin,etc.(5)Large-scale reservoir projects regulate river runoff and trap upstream sediment,which is an important factor leading to the change of water and sediment in main rivers in China;Terraces,dams and vegetation restoration projects regulate slope runoff and sediment production,which are the dominant factors of sediment variation in branch flow. |
