Prediction of the impact of climate change on the number of heatstroke patients in Tokyo, Japan with heat-adaptation effects

Background and Aim: Heatstroke has become a serious issue in Japan. To plan future adaptation measures, it is essential to understand to what extent the number of heatstroke patients will increase. Previous studies have predicted the number of heatstroke patients; however, they did not consider the effect of heat-adaptation. In this study, we conducted a future prediction study taking the effect of heat-adaptation into consideration. Methods: Japan, with its long north-south range, has a variety of climates, and it is necessary to explore its heat-adaptation effects. Our previous study showed that there was a positive correlation between the wet bulb globe temperature (WBGT) value at which heatstroke patients start to increase (WBGT threshold) and regional climate (average daily maximum WBGT between May and September: RCWBGT). Using the relationship, we translated this geographical effect of heat-adaptation to temporal adaptation by shifting the WBGT threshold to a higher side when the RCWBGT increases in the future owing to climate change. We focused on the age groups of 65+ yr, constituting the most vulnerable age group. Five future climate change scenarios and RCP8.5 scenario were adopted. All the data utilized in this study were public domain data and are available from the corresponding website. Results: In Tokyo, the number of heatstroke patients by mid-21st century will be 2.2 times as high as that of heatstroke patients at present and 6.9 times by the end of the century without heat-adaptation; however, the corresponding numbers will be 1.4 times and 2.5 times, respectively, with heat-adaptation. Conclusions: The increase in the number of heatstroke patients was projected to substantially reduce owing to the effect of heat-adaptation. Acknowledgement: This work was supported by the Climate Change Adaptation Research Program of the National Institute for Environmental Studies. Keywords: Climate change; Wet bulb globe temperature; Heatstroke; Impact assessment