Compound effects of dams and levees reshape Yangtze flood dynamics and reveal substantial risk misestimations from ignoring levees

Rivers worldwide are facing an escalating risk of devastating floods driven by climate change, despite the extensive regulation of human infrastructures. Previous large-scale analyses of floods have reconstructed global and regional patterns by accounting for reservoir regulation; however, the critical role of levees remains largely ignored. Here, we provide a timely assessment of infrastructure-driven flood dynamics by simulating the joint influence of dams and levees across the Yangtze River Basin during 1980–2019 using the CaMa-Flood model. Results clarify the distinct and complementary roles of these structures: levees rectify peak-flow fidelity (median Nash–Sutcliffe Efficiency 0.62 at 32 validated flow stations) while dams primarily enhance low-flow accuracy (median logNSE 0.71). Ignoring levees results in a ~ 15% overestimation of annual maximum inundation area relative to dam-only assessments. Despite parameterization uncertainties, this study provides the first insights highlighting the critical role of integrating levees to accurately simulate regulated river systems and flood risk assessments.