Significant Rural Contributions to Coastal Urban Flooding Through Flow Connectivity

Coastal cities are increasingly threatened by hurricane-induced compound flooding, which occurs when heavy rainfall coincides with storm surge. While rainfall-surge interactions and other flood drivers, such as runoff from surrounding rural and urban areas, act at whole-basin scales, compound flooding has been predominantly studied in localized areas of its highest impact. Here, we leverage a multi-scale Earth system modeling framework to reproduce a hurricane-induced compound flooding event. The results show that urban flooding is mainly controlled by topographic factors (low elevation, flat slopes, and localized flow constrictions), rather than increased runoff from impervious surfaces. Importantly, runoff from rural areas, facilitated by the flow connectivity, contributes more to urban flooding for areas with inundation depth exceeding 1.7 m than local runoff (~ 77% vs. ~56%). Rainfall–surge interactions and sea-level rise exacerbate inundation depth along the coastline. However, over 90% of the compound flooding occurs on coastal wetlands, highlighting their critical buffer function during landfalling hurricanes under both present and future conditions. By resolving flooding processes across scales and components, this study identifies diverse drivers of coastal urban flooding, emphasizing the significance of both local urban and surrounding rural runoff as well as the role of wetlands in coastal flood risk assessment.