Coastal infrastructure typology and people's preference-based grey-green-hybrid infrastructure classifications using a latent class model: A case study of Japan

Following the 2011 Tohoku earthquake and tsunami in Japan, multiple lines of defence applying various approaches to structural/non-structural coastal defence has gained momentum. These changes have led to accelerate the development of hybrid infrastructure, which combines artificial and natural features, to provide essential defense functions while also harnessing the benefits of ecosystem services, including recreation and biodiversity conservation in Japan. However, the higher the number of services and stakeholder groups targeted, the lower is the capacity to maximise the delivery of each service and simultaneously fulfil the specific needs of each stakeholder group. This study conducted an online survey across Japan and obtained 861 valid responses for the analysis, elucidating the optimal balance between artificial and natural feature using a latent class model. Additionally, we examined whether the anticipated risk of the Nankai Trough earthquake and tsunami influenced perceptions of coastal infrastructure. The results showed that 81.7 % of our respondents favoured hybrid infrastructure, which can be classified into five distinct types with varying levels of grey and natural components. Furthermore, individuals who undertook personal tsunami preparedness measures, such as reviewing hazard maps and participating in evacuation drills, were more inclined to prefer hybrid infrastructure. In contrast, those who were less prepared for tsunamis or took no action tended to lean towards the exclusive installation of either grey or natural infrastructure. There was no statistically significant difference in Nankai Trough tsunami-prone area in preferable coastal infrastructure types; however, it highlighted the potential needs and importance for hybrid infrastructure to be multi-objective.