The Japan Meteorological Agency (JMA) has introduced a new term, "kokushobi," translating to "cruelly hot day," to describe days when temperatures soar to 40 degrees Celsius or above. This decision follows a particularly intense summer in 2025, the hottest since records began, where temperatures topped 41.8°C in Isesaki, Gunma Prefecture.

The term "kokushobi" emerged as the most popular choice from an online survey, which attracted nearly 478,000 responses. It received 202,954 votes, significantly edging out other contenders like “super-extremely hot day” ("cho-moshobi") and “drastically hot day” ("gokushobi"). The JMA aims to use this designation to more effectively communicate the dangers associated with extreme heat and encourage the public to take necessary precautions.

Japan has experienced consecutive years of temperatures exceeding 40°C, with the agency noting that this trend is likely driven by global climate changes. Acknowledging the increasing frequency and intensity of heatwaves, the JMA has been proactive in raising public awareness and providing guidance during periods of extreme weather.

In conjunction with this new terminology, the JMA already categorizes days based on rising temperatures, using terms like "natsubi" for summer days over 25°C, "manatsubi" for midsummer days over 30°C, and "moshobi" for extremely hot days over 35°C. The addition of "kokushobi" marks a significant step in communicating the severity of Japan's evolving climate challenges.

As the nation braces itself for the upcoming summer, climate experts and health officials stress the importance of preparedness as temperatures are projected to remain above normal levels, further underscoring the need for effective public health strategies to mitigate the impacts of heat on vulnerable populations.