Using Multidisciplinary Analysis to Develop Adaptation Options against Extreme Coastal Floods

Long-term flood risk adaptation and decision making are complex because the future is full of deep uncertainties. Flexibility and robustness can be used to deal with future uncertainty. This study developed an integrated modeling framework that extends previous studies to the spatial domain to assess the future flood risks and the cost and benefit of three adaptation measures for four types of buildings in Shanghai. Real options analysis (ROA) and dynamic adaptive policy pathways (DAPP) were integrated to develop a dynamic adaptation pathway and identify robust adaptation options. The results show that: (1) Sea level rise and land subsidence will significantly exacerbate the flood risks in Shanghai; (2) Among the three flood control measures, wet-floodproofing has the best economic performance in terms of both the net present value and the benefit/cost ratio, followed by dry-floodproofing, and elevation; (3) Dry-floodproofing can be used at the beginning of the future period (2030-2100), and it can be replaced by wet-floodproofing in 2035-2042; the elevation measure also shows good performance at the beginning of implementation, but its performance will decline after 2041-2045; (4) The combined strategy of dry- and wet-floodproofing in 2044-2046 and a hybrid strategy combining the three measures should be the optimal solution for reducing the flood risks in 2047-2051. The methodology developed in this study can provide insights for coastal cities to formulate cost-effective and feasible adaptation strategies in a deeply uncertain future.