Direct and Functional Hazard Exposure of Urban Healthcare Systems Under Estimated Tsunami Inundation Zones: A...

Background Tsunami disasters pose significant challenges to urban healthcare systems, particularly in densely populated coastal metropolitan areas. Although previous studies have examined hazard exposure and evacuation dynamics, limited attention has been paid to how healthcare system vulnerability arises from the combined effects of hazard exposure and population redistribution. This study examined the spatial relationships among estimated tsunami inundation zones, population distribution, and healthcare institutions in Osaka City, Japan, to identify structural vulnerabilities in urban healthcare systems. Methods A cross-sectional geographic information system (GIS)-based spatial analysis was conducted using publicly available secondary data from official sources, including the Hazard Map Portal Site (MLIT) and national census data (e-Stat). Spatial relationships among estimated tsunami inundation zones, population distribution, evacuation-related facilities, and medical institutions were examined. Spatial overlay analysis identified medical institutions located within inundation zones, and a nearest-neighbor approach was used to estimate changes in the population served by each institution under tsunami conditions. Results The analysis suggests a dual structure of healthcare system vulnerability. First, several healthcare institutions in Nishinari Ward were located within estimated tsunami inundation zones, indicating direct physical exposure and potential functional disruption. Second, medical institutions located outside inundation zones experienced substantial increases in the surrounding population under tsunami conditions, with some institutions showing up to a 5.5-fold increase compared to baseline levels. This reflects indirect functional exposure due to concentrated healthcare demand. Conclusion These findings suggest that disaster vulnerability in urban healthcare systems can be characterized by a dual structure consisting of direct physical exposure and indirect functional exposure. In large coastal metropolitan areas, effective disaster preparedness should consider not only static hazard exposure but also dynamic processes such as population redistribution and cross-boundary healthcare demand. Integrating these perspectives is important for developing more resilient healthcare planning strategies.