Energy-sediment relationship model based on runoff erosion power and its improvement in typical Yangtze River basin

Based on the concept of runoff erosion power, to establish the basin energy-sediment relationship model can provide theoretical support for the accurate simulation of sediment load change and soil and water conservation planning in the Yangtze River Basin. In this study, the typical watersheds of the Yangtze River and its typical small watersheds were taken as the research objects. By collecting the daily precipitation, runoff and sediment data of three typical watersheds including Jinsha River Basin, Jialing River Basin and Xiangjiang River Basin from 1965 to 2018, and the rainstorm flood scale precipitation, runoff and sediment data of two typical small watersheds including Wan 'an and Lizikou from 2014 to 2020, the runoff erosion power and rainfall erosivity were used to compare and analyze the advantages and disadvantages of the relationship between runoff and sediment load, rainfall erosivity and sediment load, and runoff erosion power and sediment load at different spatial and temporal scales. The superiority of the relationship between runoff erosion power and sediment load was analyzed, and the inconsistent changes of the relationship between runoff erosion power and sediment load were identified, so as to improve the model of the relationship between runoff erosion power and sediment load and improve the simulation accuracy of sediment load in the watershed. The results showed that: (1) In most cases, the performance of runoff erosion power and sediment load relationship was always better than that of runoff and sediment load relationship, rainfall erosivity and sediment load relationship in three typical watersheds and two typical small watersheds in the Yangtze River Basin. At the event, monthly, and annual scales, the maximum R²_adj values can reach 0.94, 0.87, and 0.54, respectively. Sediment load always increased with the increase of runoff, rainfall erosivity and runoff erosion power. (2) For different time scales, the first flow Q₁ quantile was always close to 1 and the second flow Q₂ quantile was around 0.5 or higher than 0.5 when the correlation between any two flow products and sediment load in the flow sequence was high. Based on the runoff erosion power, the sediment load of watersheds at different spatial and temporal scales can be accurately calculated, which had obvious applicability. (3) With the time upscaling, the relationship between runoff and sediment load, rainfall erosivity and sediment load, and runoff erosion power and sediment load gradually deteriorated. The runoff erosion power and sediment load of the three typical watersheds had significant trends and significant change-points in some months (P<0.05). Especially on the annual scale, the sediment load showed a significant decreasing trend (P<0.05), and the runoff erosion power and sediment load relationship showed inconsistent changes. (4) Reservoir construction and vegetation increase were important reasons for the deterioration of the runoff erosion power and sediment load relationship in the basin, which were significantly negatively correlated with sediment load (P<0.001). By considering the reservoir index and NDVI to improve the runoff erosion power and sediment load relationship model, R² can be increased by 27.28%-97.62%. The research results will support the development of new watershed sediment prediction models and serve the ecological protection and high-quality development of the Yangtze River Basin.