Launching criteria of ‘Heatstroke Alert’ in Japan according to regionality and age group

Abstract

To reduce heatstroke cases, the Japanese government launched “Heatstroke Alert” in 2020. In this initiative, an alert is issued when the daily maximum wet bulb globe temperature (WBGT) is expected to reach or exceed 33 °C. However, heatstroke incidents at a daily maximum of WBGT of 33 °C can vary by regions and by age groups. In this study, we analyzed the heatstroke incidence in all 47 prefectures of Japan at the daily maximum WBGT of 33 °C, considering age groups. In addition, considering variations in heatstroke incidence by prefectures and age groups, alternative “Heatstroke Alert” criteria (AHAC) by each prefecture and age group were examined. We also analyzed the daily maximum WBGT at which heatstroke incidence starts to increase (the WBGT threshold), as this can be an additional metric to “Heatstroke Alert” for the prevention of heatstroke. The results showed that the northern region (higher latitudes) of Japan has more patients with heatstroke per population, at a daily maximum WBGT of 33 °C, than the southern region (lower latitudes), by factors of approximately 3–5, considering each age group. The suggested AHAC among 47 prefectures were 29.8 [27.7–31.4] °C for 7–17 years, 32.4 [30.2–33.9] °C for 18–64 years, and 30.8 [28.5–33.2] °C for ≥ 65 years, respectively. The northern region exhibited a lower WBGT threshold (defined as the value at which heatstroke incidence is 0.1 persons per 105 people) than the southern region by approximately 3.5–5 °C, considering each age group. The calculated average WBGT threshold among 47 prefectures was 23.2 [20.4–25.3] °C for 7–17 years, 26.3 [24.2–28.1] °C for 18–64 years, and 23.1 [20.2–25.6] °C for ≥ 65 years, respectively. These findings are expected to contribute to the reinforcement of “Heatstroke Alert” and the use of WBGT information in a more preventive manner.

Ambient temperature and preterm birth: A case‐crossover study

“…Growing awareness of global warming and heat‐related risks has prompted people to adopt effective strategies to avoid excessive heat exposure, engage in cooling behaviours and ensure adequate water intake 47 . Notably, the Japanese government's ‘Hot Temperature Alert’ initiative, launched in 2011, 48 advises individuals, particularly vulnerable groups such as pregnant women, to refrain from outdoor activities and take proper cooling measures. These efforts at individual and societal levels in Japan have likely reduced the risk of dehydration and weakened the association between high temperatures and PTBs.…”

Prediction of ambulance transport system collapse under extremely high temperatures induced by climate change

“…The regression coefficients a i and b i in equation (3) were estimated for each age group using a generalized linear model with a quasi-Poisson distribution in R. Long-term trends and seasonality were not controlled for in this calculation because Oka et al (2023b) demonstrated that although the explanatory variable in equation ( 3) was the WBGT, these treatments did not cause substantial differences in the value of a i between the non-control and control cases.…”

Evaluating Japan’s revised heat-health warning system in the face of recent escalating heat stress

“…To address the escalating challenge of heat stress, HHWS has been adopted in various cities across North America and Europe, although the specific features of these systems may vary to accommodate local climate conditions and the vulnerability of the population (Kotharkar and Ghosh 2022). In Japan, a similar HHWS was established in 2011, where a heat warning is triggered when the maximum temperature reaches or exceeds 35 • C (Oka et al 2023a).…”

“…These studies propose the use of heat stress indicators (HSIs), which comprehensively consider multiple climate variables, with a particular emphasis on the combined impact of T air and humidity. As a result of this research progress, the Japanese government has made notable revisions to the HHWS in Japan (Oka et al 2023a). Specifically, the exposure indicator has shifted from T air to Wet Bulb Globe Temperature (T WBG ), and the updated system has been carried out for the whole country since 2021 (Liljegren et al 2008, JMA & MOE 2020.…”

“…T WBG considers the joint effect of T air , humidity, wind speed, and solar radiation, and is also widely used in the United States to indicate heat category for outdoor physical activities (Liljegren et al 2008). Under this updated HHWS in Japan, a heat warning is issued when the daily maximum T WBG is predicted to reach or exceed 33 • C (Oka et al 2023a). In 2023, a total of 1232 heat-related alerts were issued across the country (MOE 2023b).…”