Climate extremes and urbanization drive flood tipping points at the city–river interface

This study presents a high‑resolution assessment of how climate extremes and rapid urbanisation interact to create flood tipping points along Philadelphia’s Schuylkill River, with clear implications for disaster risk reduction. Using street‑scale hydrodynamic modelling that integrates LiDAR terrain, river bathymetry, land‑use friction and compound drivers such as rainfall, river discharge, tides and projected sea‑level rise, the paper demonstrates how saturated soils, impervious surfaces and fragmented infrastructure amplify both pluvial and fluvial flooding. It identifies a critical threshold at the 100‑year return period, beyond which inundation expands non‑linearly, and shows that both low‑ and high‑income communities face disproportionate exposure.

The paper recommends a suite of solutions centred on compound‑aware forecasting, climate‑adaptive infrastructure and equitable resilience planning. It emphasises the need for updated design standards that jointly consider rainfall, river discharge, tides and sea‑level rise; expanded green–grey hybrid measures such as floodable parks; and improved drainage, storage and protective structures in identified hotspots. The authors conclude that the modelling framework is transferable to other coastal and riverine cities, offering a pathway for more robust, locally tailored disaster risk reduction strategies.