In recent years, there has been growing interest in green infrastructure. In particular, in the field of disaster risk reduction (DRR), the concept of “ecosystem-based disaster risk reduction” (Eco-DRR) has been proposed. Furthermore, the Japanese Ministry of the Environment has prepared a handbook to promote its use (MOE in Ecosystem-based disaster risk reduction in Japan: A handbook for practitioners. MOE, Tokyo, Japan, 2016). Therefore, in this study, we aim to review previous cases of Eco-DRR and comprehensively and integrally organize and analyze the advantages and disadvantages of Eco-DRR, compared to conventional DRR with gray infrastructure. Regarding methodology, we reviewed previous literature on representative Eco-DRR cases in Japan and the US. According to Ishiwatari (2021), the river improvement project of the Kamisaigogawa River is an exemplary initiative in Japan and was planned with the participation of citizens and academics. Similarly, in the US, Narayan et al. (Scientific Reports, 7, 2017) pointed out that following Hurricane Sandy in 2012, the damage costs were reduced by 11% in areas characterized by wetlands. We further identified some issues that need to be addressed to ensure further promotion of Eco-DRR. First, few cost–benefit analyses of Eco-DRR compared with conventional DRR utilizing gray infrastructure are present in the existing literature. The results of such analyses will be essential for evidence-based policymaking. Second, some government agencies tend to be skeptical about actively promoting the introduction of Eco-DRR, as its benefits are unclear. In other words, without cost–benefit information, it is difficult for policymakers to secure a budget for Eco-DRR. We could find few accumulated cases on Eco-DRR. Therefore, we believe that it is necessary to further develop technical standards and economic analysis methodology for Eco-DRR in future, considering that methods of conventional gray infrastructure are well established and widely applied worldwide, and various technical and economic manuals and guidelines are already available for its planning, construction, operation, and maintenance. In addition, based on the case of the Kamisaigogawa River reviewed in this study, we believe that the participation of many stakeholders, including academics, in Eco-DRR projects and the consensus-building process will be highly significant for the success of Eco-DRR projects. We also believe that the findings of this study can contribute positively to evidence-based policymaking for Eco-DRR.
