Inter- and intra-annual fluctuations and attribution analysis of runoff and sediment transport in the middle and lower Yangtze River

Assessing the changing regimes of runoff and sediment load in rivers, as well as analysing their underlying causes, is essential for maintaining the ecological integrity of rivers and promoting the sustainable development of water resources. Current methods of attribution analysis focus on accounting for the effects of climate change and human activities on inter-annual variability in streamflow and sediment. However, the contribution of individual drivers to intra-annual hydrologic variability is often overlooked. The study analysed the inter- and intra-annual fluctuations in runoff and sediment load in the middle and lower Yangtze River using a water-sediment variation attribution model, the Extreme Gradient Boosting algorithm, and the Multiple-Factor Attribution method. The results showed that human activities were responsible for over 70% of the inter- and intra-annual fluctuation in runoff and sediment load in the Yichang, Hankou, and Datong sections. Additionally, it was found that human activities were the main contributor to the reduction in both runoff and sediment load in all sections. Closer to the Yangtze estuary, human influence on intra-annual fluctuation of runoff decreases while climate change influence increases, and human influence on both inter- and intra-annual fluctuation of sediment load becomes less significant. The sensitivity of annual runoff to precipitation is greater than that of air temperature and evaporation in the Yichang, Hankou, and Datong sections. An increase of 10% in precipitation from baseline values leads to a corresponding increase of 3.13%, 2.24%, and 3.91% in runoff for the Yichang, Hankou, and Datong sections. The annual sediment load is more sensitive to changes in runoff than to precipitation, air temperature, and evaporation in each section. A 10% increase in runoff from the baseline value leads to an annual sediment load increase of 20.36%, 10.11%, and 8.78% at Yichang, Hankou, and Datong, respectively. This study provides a theoretical basis and guidance for decision-making to protect and sustainably develop the water and sediment resources in the Yangtze River Basin. The XGBoost algorithm and MFA method were coupled to perform attribution analysis of inter- and intra-annual variations of runoff and sediment load. Human activities were the primary cause of decreased runoff and sediment load in the middle and lower Yangtze River. Sediment load is susceptible to variations in runoff, which in turn is influenced by variations in precipitation. image