Cost–benefit analysis of adaptation to storm surge due to climate change in Osaka Bay, Japan

Climate change poses significant challenges and impacts to coastal communities. In order to limit future coastal flood risk, adaptation is necessary. This study presents an integrated model to simulate storm surge inundation risk in Osaka Bay under climate change and provide a cost–benefit analysis of structure adaptation strategies to reduce risk. The results show that storm surge inundation risk will increase dramatically as combined impacts of sea level rise and intensified storm surges due to global warming. Without adaptation measures, the expected annual damage cost increases from 9.85 billion JPY to 69.17 billion JPY in Osaka Bay under the projected RCP8.5 scenario to 2100. We then explore the effectiveness of structural adaptation strategies. The results indicate that raising the height of existing dikes can reduce inundation risk effectively. The benefits and costs depend on the elevated height and the discount rate. Using cost–benefit analysis, we find that upgrading by 1 m the height of existing dikes is the most cost-effective strategy for Osaka Bay. The methodology developed in this paper provides a reference for Osaka Bay and other coastal regions when they make coastal flood risk management and adaptation strategies to respond to climate change.