Quantifying flood risk redistribution: How urban pumping systems reshape regional flood patterns in plain river networks

Study region: The northern Taihu Basin, China, a highly urbanized plain river network with intensive economic development, featuring Wuxi city and its peripheral areas under severe flood pressures from both climate extremes and rapid urbanization.Study focus: Urban pumping systems effectively mitigate local flooding but may paradoxically intensify flood risks in peripheral areas through complex hydraulic transfer mechanisms. This research develops an integrated assessment framework coupling scenario-based hydrodynamic modeling with a dimensionless Water Level Safety Margin Index (Mi) to quantify spatial flood risk redistribution across plain river networks. The Mi normalizes flood hazard indicators within locally-defined flood control capacity, enabling objective cross-river and trans-regional risk comparisons.New hydrological insights for the region: This study reveals critical flood risk redistribution patterns driven by urban pumping operations in the plain river networks. Urban pumping systems significantly reduce local flood risk (93% decrease in Mi) but exhibit diminishing returns beyond optimal capacity thresholds. Concentrated urban discharges creates severe flood hotspots in upstream adjacent rivers (peak Mi=5.74) through backwater effects, while downstream areas remain relatively protected. Most importantly, hydraulic connectivity drives unexpected flood amplification in both topographically vulnerable areas (Mi >4.4) and seemingly protected high-elevation regions. These findings challenge conventional topography-based flood risk assessments and provide critical insights for coordinated urban-regional flood management in plain river networks.