The relationship between the monthly cumulative number of heatstroke cases and the mean temperature in Tokyo, Japan

Abstract Heatstroke occurrence is strongly related to atmospheric conditions, and this relationship should be understood when considering its prevention. Recent studies have improved our understanding of the relationship between heatstroke and daily atmospheric conditions in Japan. However, our understanding of their relationship at the seasonal time scale (e.g., monthly) remains inadequate. In this study, we investigated the relationship between the cumulative number of heatstroke cases and the monthly mean meteorological variables near the surface in Tokyo, Japan, during the summer season (July and August) by statistically analyzing observational data from 2010 to 2024. The results showed that for July, the temperature of the current month, and for August, the temperatures of the current and previous months were strongly related to the variation in the number of heatstroke cases. Analyses based on Poisson regression models showed that temperature explained 82% and 70% of the variation in the number of heatstroke cases in July and August, respectively. In August, the temperature of the previous month had a suppressive effect on heatstroke cases, with 50% contribution from the temperature of the current month to the number of cases. This effect may reflect natural heat acclimatization. These results show that the total monthly number of heatstroke cases in Tokyo can be estimated with some success using information on the monthly mean temperature alone. Such results are expected to be used for the seasonal prediction of heatstroke risk and the assessment of health risks caused by global warming.