A General Framework of Vulnerability Assessment to Typhoon Storm Surge Inundation in Coastal Cities

Abstract

Rapid urban expansion in coastal mega-cities (cities with populations over 10 million) leads to increased land demand and vulnerability to hazards as significant numbers of people are economically and socially disadvantaged. The high vulnerability of coastal mega-cities to storm surge inundation means both infrastructure and their populations are subject to significant threat. Therefore, it is vital to assess coastal inundation vulnerability to storm surge and project the change of future vulnerability under climate change scenarios to ensure a sustainable future for these cities. This thesis develops a general framework to assess the coastal inundation vulnerability to storm surge hazard. This vulnerability assessment framework aims to provide a general approach that could be easily implemented, and has low requirements for computation time and data. A case study (Shanghai) reveals how coastal communities are vulnerable to storm surge inundation and demonstrates how better preparedness and higher resilience could be built to reduce such vulnerability through adaptation strategies. Firstly, historical storm surge and typhoon activities in Shanghai were reviewed. Following by a brief review on the current status of coastal protection works, land use change and reclamation projects in Shanghai. Secondly, a two domain multi-nested typhoon storm surge model was established for coastal and regional scale in Shanghai to simulate storm surge inundation under two selected historical typhoons Winnie (1997) and Wipha (2007). Subsequently, the spatial distribution and variation of inundation vulnerability of six land use types in Shanghai to typhoon storm surge were calculated and analysed by a new stage-damage curve system in this study. Simulated results of two historical typhoons suggested that high vulnerability to storm surge inundation was mainly located in the south Shanghai and west Chongming Island, while low vulnerability was observed in the west Shanghai. It is also noticed that although the inundation depth in the city centre was lower than the coastal area, the inundation vulnerability was still high as this area was mainly covered by highly vulnerable urban and built-up land. Thirdly, the future inundation vulnerability of Shanghai was projected, including consideration of climate change and land subsidence. The impacts of extreme typhoon, sea level rise, and land subsidence on the vulnerability to storm surge inundation over Shanghai were analysed. Under sea level rise and land subsidence scenarios, the inundation vulnerability of Shanghai to storm surge is likely to increase significantly by 2100. Results also shown 78 % of the ongoing reclamation land in Hengsha Island is likely to experience a high vulnerability of over 80 % under 500-year return period typhoon activities and 100 % under 1000-year return period typhoon. Lastly, based on the understanding of the inundation vulnerability of different land use types built in this study, future coastal vulnerability adaptation strategies were then proposed for Shanghai. The performances of land use planning and three potential coastal protection strategies were examined under climate change scenarios. Results suggested the inundation vulnerability cannot be mitigated by applying different land use patterns, and a soft engineering approach could be more effective than hard engineering approach to mitigate inundation vulnerability in Shanghai under sea level rise and land subsidence scenarios.