Sediment change under climate changes and human activities in the Yuanjiang-Red River Basin

Both the climate change and human activities are the major influence factors to the sediment change in mountainous rivers. Based on the over 40 years’ record, suspended sediment loads (SSL) change at the Manhao gauging station in the lower reaches of Yuanjiang River (upper Red River). In this paper, the variation of the sediment and its drivers were analyzed through different methods such as synchronous data comparison, traditional correlation, linear regression, and Granger causality. The results show that (1) the general trend of the annual average sediment concentration (SSC) and SSL at Manhao station is increasing from the 1960s to the 1990s, and there is a quick change period after 1984; (2) the SSL and SSC at Manhao station, during different periods of the 1960s, 1970s, 1980s and 1990s, are 1.87, 2.49, 3.12, 3.63 kg/m³, and 28.7×10⁶, 40.3×10⁶, 44.1×10⁶, 60.3×10⁶ t/a, respectively; (3) the correlation analysis and the Granger causality test proved that the climate changes in the catchment were the main driving factors to the sediment variation in the period of 1960s and 1990s, but the influence by the mountainous human actions on the sediment change is stronger than that by the local climate changes in the 1970s and 1980s; (4) the correlation between the sediment changes and the forest coverage change is negative, which further proves that the sediment changes are strongly affected by the human activities in the basin.