THE ASAHI SHIMUN
April 23, 2025 at 14:28 JST
Visitors wait in line for a water dispenser at the Osaka Kansai Expo in Osaka's Konohana Ward on April 19. (Hana Matsuo)
The government on April 23 started 2025 operations of both its ordinary and special heatstroke alert systems to warn the public about dangerous temperatures and weather conditions.
Operated by the Japan Meteorological Agency and the Environment Ministry, the ordinary system issues an alert when the heat stress index is expected to hit 33 or higher within any of the country’s 58 forecast districts.
The index is calculated based on temperature, humidity, sunlight and other factors.
The district in question will receive a heatstroke alert at 5 p.m. on the day before the index reaches 33 or at 5 a.m. on the day of concern.
Under the special heatstroke alert system, a warning will be issued when the heat stress index is forecast to reach 35 or higher at all observation points within a prefecture.
The warning will be issued at 2 p.m. on the day before the extremely dangerous conditions.
The special heatstroke alert system started in 2024, but it has issued no warnings so far.
However, summer temperatures in Japan have risen in recent years, and an unprecedented prefecture-wide heat stress index of 35 is not out of the question.
According to the JMA, the average temperature in summer last year was 1.76 degrees higher than average and matched the 2023 summer as the hottest since such statistics were first compiled in 1898.
Average temperatures in May are expected to be normal or higher from western through northern Japan, while higher-than-average temperatures are forecast across the country from June through August.
The alert systems will be active until Oct. 22.
The government is concerned that visitors to the Osaka Kansai Expo will be at risk of heatstroke.
“We hope visitors will enjoy the expo while taking precautions against heatstroke, such as frequently drinking fluids and taking in salt,” Environment Minister Keiichiro Asao said at a news conference on April 15.
(This article was written by Nami Sugiura and Shoko Rikimaru.)
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