Changing Flood Patterns in the Yangtze River: Roles of Climate, Dam Regulation, and Urbanization in Altering Hydrological Processes

Abstract

The middle and lower reaches of the Yangtze River (MLYR), China's most flood-prone region, have experienced significant changes in flood regimes under climate change and intensive human activities. To elucidate the hydrological processes driving these changes, this study combined a random forest model with the Mann–Kendall test to analyse flood characteristics and influential factors. Results reveal: (1) Abrupt flood stage declines post-2003 (Three Gorges Dam operation) followed by increases post-2016, primarily due to urbanisation amplifying runoff and accelerating drainage discharge into river channels; (2) concentration of flood peaks in July, driven by reservoir-induced baseflow elevation synchronising with intensified monsoon rainfall; (3) Spatial heterogeneity in flood severity, where middle reaches face high-magnitude floods from flow convergence, while lower reaches experience frequent inundation due to tidal-urban interactions. Mechanistically, we demonstrate how dam operations redistribute flood risk (e.g., prolonging high stages in Dongting Lake) and urbanisation reconfigures flood pathways, converting pluvial to fluvial flooding. These findings underscore non-stationary flood dynamics in regulated basins globally, necessitating adaptive strategies integrating real-time morphodynamic feedbacks and nature-based urban water retention. This study advances hydrological understanding of how human infrastructure and climate interact to reshape flood processes in large river systems.