Background <p>Flood is one of the most frequent and devastating natural hazards. The flood exposure of economically vibrant coastal low-lying areas shows a significant increase due to human migration and economic activities.</p> Purpose <p>The impact of demographic and economic development changes on flood risk remains unclear. The assessment of the impact of flood hazards on population and economic productivity in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is necessary.</p> Methods <p>The population and economic productivity exposed to floods in GBA from 2000 to 2020 are assessed by integrating flood modeling with statistical analysis of historical data. Sustainable areas for development in GBA are evaluated by integrating road networks and national standards from a flood control perspective.</p> Results <p>Pearson correlation analysis indicates that the correlation between relative flood exposed migrants and economic productivity is 0.93, significantly higher than that of local residents. 39.45% of lands are sustainable for development and migration in GBA, of which 14.23% are in the perfect level.</p> Conclusion <p>This study will provide new insights into the relationships between population dynamics, migration patterns, and economic productivity with flood risks in major urban agglomerations, while offering strategic recommendations for sustainable development.</p>