Japan experienced its first officially designated “cruelly hot day” on Tuesday, with temperatures in three central cities surpassing 40°C, as a prolonged heatwave gripped the archipelago. The Japan Meteorological Agency (JMA) introduced the term kokushobi this year to sharpen public warnings about extreme heat, and the threshold was crossed in Tajimi, Gujo, and Toyota, while the mercury hit 40.5°C in Kuwana on Wednesday. Across 914 observation points, 278 stations recorded temperatures above 35°C, the previous highest alert level.

The human cost has been immediate and severe. The Fire and Disaster Management Agency reported that 10,857 people were taken to hospital by ambulance for heatstroke in the week through Sunday, a 2.4-fold increase on the previous week, with 14 deaths and 321 cases requiring hospitalisation of at least three weeks. On Tuesday alone, the Tokyo Fire Department said 287 people were transported to hospitals with suspected heatstroke, the highest single-day tally since comparable records began in 2022. Local authorities in Tochigi, Niigata, and Kanagawa prefectures confirmed additional fatalities, including an 84-year-old farmer found unconscious in a greenhouse and a man in his 40s discovered dead on a street.

With heatstroke alerts active in 41 of Japan’s 47 prefectures, the Tokyo Metropolitan Government expanded its “Cool Biz” campaign, urging office workers to abandon suits for shorts, T-shirts, and trainers to reduce air-conditioning use and ease discomfort. The initiative, first launched in 2005 by Governor Yuriko Koike, has drawn mixed reactions. A June survey by a cosmetic clinic found 53.5% of respondents opposed wearing shorts at work, with some women coining the term sunehara, or “leg hair harassment,” to describe discomfort at seeing male colleagues’ bare legs. Officials stressed the guidance is voluntary, not a dress code.

Japan’s summers have grown markedly hotter, with average temperatures rising about 1.3°C over the past century, according to the JMA. Last year, heatstroke deaths exceeded 2,000 for the first time, and more than 100,000 people were hospitalised. The new kokushobi category reflects the increasing frequency of 40°C days, though it does not trigger mandatory measures. Emergency officials have described the heat as a “disaster,” and the JMA warns that high temperatures will persist into next week. The full human cost remains provisional, with authorities urging continued precautions.