Research and reflections on the compilation of flood risk maps for typical islands in Yangtze River estuary: A case study of Chongming Island

As China's third-largest island (approximately 1, 267 km²), Chongming Island serves as both an ecological barrier and core economic zone at the Yangtze River estuary. It has long faced compounded threats from typhoons, heavy rainfall, high tides, floods, and urban flooding. Existing domestic models struggle to accommodate the island's complex tidal river networks and integrated water management needs, hindering precise flood risk assessment. This study innovatively develops a "slope runoff-one-dimensional river hydrodynamics-two-dimensional inundation hydrodynamics" deep coupling model, integrating hydrodynamics theory with GIS spatial analysis. By optimizing computational efficiency through CPU-GPU heterogeneous parallel processing, the model evaluates 71 comprehensive flood scenarios to quantify key parameters including inundation depth, duration, and flow velocity. Findings reveal that Chongming Island exhibits the widest coverage of stormwater flooding risks (282.88–772.33 km²) and the highest average inundation depth (0.52 m) due to seawall breaches, while historical flood impacts remain relatively limited. The model's multidimensional validation confirms its accuracy meets technical requirements from the Ministry of Water Resources, providing scientific support for developing flood risk maps and optimizing flood control strategies for estuarine islands.