Japanese authorities have announced the adoption of a new term for days when temperatures reach or exceed 40 degrees Celsius. After the country experienced its hottest summer on record last year, the term "kokushobi," which translates to "extremely hot day," "brutally hot," or "cruelly hot," is now being used in domestic media. The name was selected as the most preferred in a national online poll, while the proposal "extremely hot day" ranked second.
Extreme weather events, such as heatwaves, are becoming increasingly frequent and intense worldwide, driven, according to experts, by human activities like burning fossil fuels. The new description introduced by the Japan Meteorological Agency (JMA) uses the word "koku," meaning harsh or cruel, to describe the heat. The survey was conducted in February and March and received about 478,000 responses, with participants choosing their preferred term from 13 options to describe the hottest days.
Japan already uses terms for days above 25°C, 30°C, and 35°C, but this new term aims to describe even more extreme temperatures. This change comes after the country experienced record temperatures last year. The summer of 2025 was the hottest since records began in 1898, with national average temperatures 2.36°C above normal. Temperatures exceeded 40°C on nine days during the June-August period, with a new national record of 41.8°C in the city of Isesaki.
The total number of extremely hot days also broke the previous record set in 2024. Tokyo recorded 25 days above 35°C (compared to an average of 4.5), while Kyoto had 52 days above this temperature (against an average of 18.5). For this summer as well, JMA forecasts a high probability of above-normal temperatures in Japan during the June-August months.