Quantitatively decoupling the relationships between discharge and sediment yield during flood events in China's Loess Plateau

Changes of discharge (Q) and sediment yield (SSY) during flood events provide critical insights for flood disaster prevention and control. However, our understanding of the long-term variations and driving factors of Q-SSY relationships during flood events remains limited. This study examined the variations in Q, SSY and sediment rating curves (SSY = aQ^b) during maximum flood events (one, three, and five) across fifteen catchments in the China’s Loess Plateau during 1956-2019. The partial least squares-structural equation modeling (PLS-SEM) was used to quantitatively decouple the effects of driving factors (precipitation, soil, vegetation, topography, and soil and water conservation measures (SWCMs)). There was a significant declining trend in both Q and SSY during flood events across catchments, but the contribution of these events to annual SSY significantly increased by 41.48% during 1956-2019, underscoring the critical role of floods in sediment transport. The Q-SSY relationship during flood events weakened over time, with coefficient a decreased and index b increased. In addition, 44 - 49% and 36 - 51% of the changes in a and b can be attributed to the comprehensive effects of the five factors, respectively. The direct effects of vegetation (-0.921) and precipitation (0.616) on coefficient a were significant. Index b was principally dominated by SWCMs and vegetation, and the effects diminished from one to five flood events. These findings highlight the importance of increased vegetation cover and effective SWCMs in mitigating sediment transportation processes, and informs the development of tailored sediment management strategies for the Loess Plateau and similar regions.