Assessing Pedestrian Exposure to Heat via the Wet-Bulb Globe Temperature Using Mobile Phone Location Data and Urban Thermal Simulations

The recent rise in temperatures in urban areas has raised concerns about various health problems, such as heat-related illnesses. This study quantified the number of individuals exposed to outdoor heat during the daytime in the summertime waterfront area of Tokyo. Conventional meteorological observation and administrative data are insufficient for high-resolution analyses of people flow and heat conditions in urban environments. Therefore, this study introduced a new methodology combining urban computational fluid dynamics (CFD) and mobile phone global positioning system (GPS) data. A numerical simulation was performed to estimate the wet-bulb globe temperature (WBGT) by analyzing fluid dynamics and radiation models. The WBGT in parks was determined to be approximately 27 °C, while the on-road temperature exceeded 29 °C. Simultaneously, pedestrian density was assessed by collecting high-resolution mobile phone GPS data, revealing that pedestrians concentrated near stations, office areas, and shopping districts within a 5 km × 5 km area. Furthermore, a review of heat stroke cases (2010–2020) indicated that combining heat and people flow yielded stronger correlations with the number of heat stroke cases than considering heat alone. Finally, a new heat risk index was established, integrating heat, people flow, and aging rate, which more accurately predicted the heat stroke cases.