High-resolution outdoor heat-risk modeling for city central areas with applications to Tokyo and Lyon

Abstract

Owing to climate change, urbanization, and population shifts, heat risks in cities are projected to rise. This work aims to introduce a flexible approach for mapping outdoor heat risks by individually constructing, normalizing, and combining its four key components – hazard, exposure, vulnerability, and adaptive capacity – as recommended by the International Panel on Climate Change. The methodology was demonstrated by constructing 500-m hourly-varying outdoor heat risk maps of elderly population over two city-central areas (Tokyo and Lyon) of distinct geophysical features and demographic conditions during a summer day in 2022. The hazard component was described using a 2-m simulation of heat-stress index (wet-bulb globe temperature), which accounts for urban surface details. Vulnerability, exposure, and adaptive capacity were then defined as functions of hourly 500-m population changes, open-space ratios, and proximity to health centers, respectively. During the selected dates in Tokyo’s and Lyon’s central areas, significant spatiotemporal variations emerged in daytime elderly heat risk due to their unique urban landscapes, local climates, and senior population mobility patterns. Meanwhile, reductions in elderly population movement resulted in low outdoor vulnerability despite the peak heat hazard condition during the noontime. This work highlights the usefulness of the proposed approach, the prevailing complexities of detailed risk mapping over city-central areas, and the utility potential of increasing high-quality geospatial datasets.