Abstract
Decisions on coastal cities flood adaptation are complicated by deep uncertainty about sea level rise, subsidence and socioeconomic trends, increasing the chance of under- or over-investment. Frameworks have been proposed to plan coastal adaptation in urban settings. In this study, we expand those frameworks to include elements critical to rational decision-making in coastal cities under deep uncertainty. Our framework, trained on the city of Shanghai, includes compound flood modeling, flood risk analysis, design and quantitative simulation of adaptation strategies, cost-benefit analysis, trade-off analysis and formulation of dynamic adaptive policy pathways (DAPP). We include land subsidence in modeling flood scenarios; we compute a diverse set of flood impacts on multiple sectors; we evaluate several techniques of cost-benefit analysis; and we include multiple adaptive strategies against compound flooding (i.e., pluvial, fluvial, coastal). We show that the hard adaptation strategies (e.g., storm-surge barriers and storage tank) can successfully reduce future increase in risk generated by sea level rise, land subsidence and socioeconomic development, by 58%~94%. In contrast, soft adaptation only generate considerable benefits when integrated with hard adaptation into hybrid strategies. A hybrid strategy that combines storm-surge barrier and wetland creation most effectively reduces flood damages and casualties, and yields promising co-benefits. We formulate DAPP for robust and flexible decision-making over time for the coming decades, which open up the decision-making space and help overcome policy paralysis due to deep uncertainty.
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