The Water-Sediment Response Relationship and Driving Factors of the Main Stream of the Lower Yellow River

Abstract The hydrological processes of surface rivers are critical for sustaining their ecosystems. Understanding the dynamics of river runoff and sediment transport under changing environmental conditions is vital for the protection and management of riverine ecosystems. In this study, mathematical statistics and the Copula function were applied to reveal the evolutionary trends of runoff and sediment in the main channel of the lower Yellow River. By integrating hydrological indicators with the Range of Variability Approach (IHA-RVA), we quantitatively assessed the impacts of environmental changes on runoff and sediment dynamics, and further conducted an attribution analysis. The results showed that: (1) Both runoff and sediment experienced significant declining trends, with abrupt shifts detected in the 1980s and 1990s, respectively. (2) The synchrony between runoff and sediment was generally high (65–89%), but decreased from upstream to downstream and was weaker after the abrupt change points. (3) Runoff exhibited moderate alterations (53–62%) at all hydrological stations, whereas sediment showed greater changes (64–82%), with variability gradually decreasing along the flow path. The strongest correlation was found between monthly flow and sediment transport index. (4) Runoff variability was primarily driven by human activities, while sediment changes were mainly attributed to sediment production processes, with the contribution of these processes declining downstream. These findings suggest that the natural hydrological rhythm can be partially restored through targeted human interventions.