Debris flows are one of the natural disasters that frequently occur in mountain areas, usually accompanied by serious loss of lives and properties. One of the most used approaches to mitigate the risk associated to debris flows is the implementation of early warning systems based on well calibrated rainfall thresholds. However, many mountainous areas have little data regarding rainfall and hazards, especially in debris flow forming regions.

Shanghai is a low-lying city (3–4 m elevation) surrounded on three sides by the East China Sea, the Yangtze River Estuary, and Hangzhou Bay. With a history of rapid changes in sea level and land subsidence, Shanghai is often plagued by extreme typhoon storm surges. The interaction of sea level rise, land subsidence, and storm surges may lead to more complex, variable, and abrupt disasters. In this paper, we used MIKE 21 models to simulate the combined effect of this disaster chain in Shanghai.