Heatstroke Alerts and Cases Rise in Japan in 2024

According to the Japan Meteorological Agency, heatstroke alerts are issued in each of 58 forecast areas across Japan when the wet bulb globe temperature (WBGT) heat index is predicted to be 33 or above. Information about the alerts can be viewed on the Ministry of the Environment’s Heat Illness Prevention Information website and it is also possible to register with a mail subscription service (Japanese only) to receive alerts as they occur.

WBGT is a heat index aimed at preventing heatstroke that is estimated using factors such as temperature, humidity, and intensity of solar radiation. In recent years, WBGT meters have also started being sold in the general market. When the index is 28 or above, the number of heatstroke cases rapidly increases.

A public heatstroke alert system began operating nationwide from fiscal 2021. The first year saw 613 alerts, but this number nearly tripled to 1,722 in fiscal 2024, which was the fourth year of the system being in place. Special alerts that were introduced in fiscal 2024 for anticipated future situations when the heat index is 35 or higher have not yet been applied.

Japan began its heatstroke alert system for summer 2025 on April 23, which will run until October 22.

The JMA reported that there were a record 97,578 cases of people needing emergency transportation due to heatstroke from May to September 2024. Around 65% of those transported were diagnosed with minor symptoms, with the remainder being hospitalized with medium to severe symptoms. A total of 120 people (0.1%) died before they reached medical facilities.

Around 60% of patients were seniors aged 65 and above, while other adults aged 18 to 64 accounted for around 30%.

(Translated from Japanese. Banner photo: People staying cool under a mist shower in central Tokyo in the soaring heat of August 2024. © Jiji.)