日本气象厅（Japan Meteorological Agency，JMA）于星期五正式宣布，将最高气温达到40°C（104°F）或以上的日子称为「kokushobi」；该词意指「极端酷热日」，但尚无正式中文对应。该名词通过近50万票的公民投票确定，体现出公众参与。作为一个高度灾害敏感国家，日本长期建立了高度规范的灾害风险传播制度，JMA 希望透过制度化命名提升警觉、改善政府与企业在高温风险下的应对。
日本去年创下历史上最炎热的夏季；根据日本气象资料，在历史前20高温记录中，有8项发生于2025年7月下旬至8月上旬，占比40%。极端高温的公共卫生冲击极其严重：过去5个月期间，因中暑住院的人数刷新纪录，达到100,000人。JMA官员认为，这些数据显示「kokushobi」有必要进入正式用语体系，以将风险沟通从一般警告提升为可行为化、可治理的分级概念。
此命名补充了既有分级：35°C以上为「extremely hot day」，30°C以上为「midsummer day」，25°C以上为「summer day」。公众曾另提出「sweat-drenched heat day」等其他称呼。JMA也提醒，今年夏季高温风险上升，并指向未来几个月El Niño（厄尔尼诺）机率上升；这一现象通常令日本及南亚、东南亚地区更炙热。Alexander Pui（九州大学）指出，此举如成功，可能形成可被其他地区借鉴的模型。
On Friday, the Japan Meteorological Agency (JMA) formally announced that days with a maximum temperature of 40°C (104°F) or higher will be designated “kokushobi,” meaning a severely hot day without an official translation. The term was selected through nearly 500,000 votes, reflecting public participation. As a highly disaster-prone nation, Japan has long built a tightly regulated risk-communication system for weather emergencies, and JMA says formal naming is meant to raise awareness and improve responses by government and corporations when heat risk is extreme.
Japan had its hottest-ever summer last year; according to JMA records, 8 of the top 20 highest temperatures on record were measured in late July to early August 2025, which is 40%. Public-health impacts were severe: a record 100,000 people were hospitalized for heat stroke during a five-month period. JMA sees this volume of morbidity as evidence that formal temperature-language matters, shifting heat from a warning signal to an operational risk category people can understand and act on.
The new term expands Japan’s existing official heat categories: 35°C and above is an “extremely hot day,” 30°C and above is a “midsummer day,” and 25°C and above is a “summer day.” Citizens even suggested alternatives such as “sweat-drenched heat day.” JMA had already warned that this summer is likely hotter, noting growing odds of El Niño in coming months; that climate pattern typically drives above-normal heat in Japan and in South and Southeast Asia. Alexander Pui of Kyushu University said the crowdsourced naming approach could become a template beyond Japan if successful.