Simulating and mapping the risk of surge floods in multiple typhoon scenarios: a case study of Yuhuan County, Zhejiang Province, China

We propose a scenario-based method for simulating and mapping the risk of surge floods for use by local authorities concerned with public safety and urban planning in coastal areas. Focusing on the triad of hazard, vulnerability and adaptation capability, we estimate the comprehensive risk and display its spatial distribution using the raster calculation tool in ArcGIS. The detailed methodology is introduced via a case study of Yuhuan, an island county in Zhejiang Province, China, which is frequently affected by typhoon storm surges. First, we designed 24 typhoon scenarios and modeled the flood process in each scenario using the hydrodynamic module of MIKE 21. Second, flood depth and area were used for hazard assessment; an authorized indicator system of land use categories and a survey of emergency shelters were used for vulnerability and adaptation capability assessment, respectively; and a quantified model was used for assessment of the comprehensive risk. Lastly, we used the GIS raster calculation tool for mapping the risk of storm surges in multiple typhoon scenarios. Our principal findings are as follows: (1) Seawalls are more likely to be overtopped or destroyed by more severe storm surges with increasing typhoon intensity. (2) Most of the residential areas with inadequate emergency shelters are highly vulnerable to flood events. (3) As projected in the risk mapping, if an exceptional typhoon with a central pressure of 915 or 925 hPa made a landfall in Yuhuan, a wide range of areas would be flooded and at high risk. (4) Determining optimal strategies based on identification of risk-inducing factors is the most effective way of promoting safe and sustainable development in coastal cities.