The term - kokushobi - translates to "cruelly hot", "brutally hot" or "severely hot", and comes after Japan's hottest summer on record.
2 days ago
Mallory Moenchand
BBC Weather
David Mareuil/Anadolu via Getty Images
Japan has unveiled a new name for days that reach 40C (104F) or above, after the country experienced its hottest summer on record last year.
The term - kokushobi - has been translated as "cruelly hot", "brutally hot" or "severely hot" day by Japanese and international media.
The name emerged as the most popular in a national online survey, with "super extremely hot day" in second place.
Extreme weather events like heatwaves are becoming more common and more intense around the world, fuelled by human activities such as the burning of fossil fuels.
The description, introduced by Japan's Meteorological Agency (JMA) on Friday, uses koku - meaning harsh or cruel - to describe the heat, the Japan Times newspaper reported.
The survey was conducted in February and March and received roughly 478,000 responses, in which people picked their preferred term among 13 options to describe the hottest day.
Japan already has terms for days over 25C, 30C and 35C.
The new word for even hotter weather comes after record-shattering heat hit Japan last year.
Summer 2025 was the hottest since records began in 1898 - with average temperatures nationwide 2.36C above average.
Temperatures reached 40C-plus on nine days between June and August, with a new national peak of 41.8C in the city of Isesaki.
The cumulative number of extremely hot days also surpassed the previous record set in 2024.
For example, Tokyo recorded 25 days over 35C, compared with an average of just 4.5 days. Kyoto logged 52 days above the same temperature, compared with an average of 18.5 days.
This summer, JMA forecasts a high probability of above-normal temperatures in Japan from June to August.
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