Strategies for increasing tsunami shelter accessibility to enhance hazard risk adaptive capacity in coastal port cities: a study of Nagoya city, Japan

Coastal areas face a significant risk of tsunami after a nearby heavy earthquake. Comprehensive coastal port cities often complicate and intensify this risk due to the high vulnerability of their communities and liabilities associated with secondary damage. Accessibility to tsunami shelters is a key measure of adaptive capacity in response to tsunami risks and should therefore be enhanced. This study integrates the hazards that create risk into two dimensions: hazard-product risk and hazard-affected risk. Specifically, the hazard-product risk measures the hazard occurrence probability, intensity, duration, and extension in a system. The hazard-affected risk measures the extent to which the system is affected by the hazard occurrence. This enables the study of specific strategies for responding to each kind of risk to enhance accessibility to tsunami shelters. Nagoya city in Japan served as the case study: the city is one of the most advanced tsunami-resilient port cities in the world. The spatial distribution of the hazard-product risk and hazard-affected risk was first visualized in 165 school district samples, covering 213 km² using a hot spot analysis. The results suggest that the rules governing the distribution of these two-dimensional (2-D) risks are significantly different. By refining the tsunami evacuation time-space routes, traffic-location-related indicators, referring to three-scale traffic patterns with three-hierarchy traffic roads, are used as accessibility variables. Two-way multivariate analysis of variance (MANOVA) was used to analyse the differences in these accessibility variables to compare the 2-D risk. MANOVA was also used to assess the difference of accessibility between high-level risk and low-level risk in each risk dimension. The results show that tsunami shelter accessibility strategies, targeting hazard-product risk and hazard-affected risk, are significantly different in Nagoya. These different strategies are needed to adapt to the risk.