The Environment Ministry and the Japan Meteorological Agency plan on Wednesday to begin issuing alerts on the risks of heatstroke.
The alert is issued when authorities determine the risk to the public of suffering from heatstroke is high.
Initially, the ministry and the agency plan to implement the alert system on a trial basis in Tokyo and eight prefectures in the Kanto and Koshinetsu regions. They plan to expand the coverage nationwide in the next fiscal year.
The alert system relies on the Wet Bulb Globe Temperature (WBGT), which calculates the heat factor based on air temperature, level of humidity and quantity of solar irradiance.
When the WBGT is 33 or higher, the ministry and the agency will issue the alert in each prefecture. In addition, if a WBGT figure of 33 or higher is in the next-day forecast, an alert will be issued.
The benchmark is based on analyses of WBGT figures and the number of patients who have been transported to hospitals because of heatstroke over the past five years in Tokyo.
The analyses found when the WBGT is at least 33, both the number of heatstroke patients who are left in serious condition and deaths rapidly increased.
The ministry and the agency anticipate the alert being issued about seven times between May and September.
Ministry and agency officials said the public must consider high temperatures to be on par with disaster levels when the alert is issued, and take thorough measures to prevent heatstroke by drinking water or using air conditioners.
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