Is there any escaping Japan\u2019s summer \u9177\u6691 (kokusho, extreme heat)?<\/p>\n
In April, the \u6c17\u8c61\u5e81 (kish\u014dch\u014d, Japan Meteorological Agency) released a bulletin titled \u6700\u9ad8\u6c17\u6e29\u304c40\u5ea6\u4ee5\u4e0a\u306e\u65e5\u306e\u540d\u79f0\u3092\u300c\u9177\u6691\u65e5\u300d\u306b\u6c7a\u5b9a (Saik\u014d kion ga yonj\u016b-do ij\u014d no hi no meish\u014d o \u201ckokusho-bi\u201d ni kettei, The name \u201cintense heat day\u201d has been officially adopted for days when the maximum temperature reaches 40 degrees Celsius or higher).<\/p>\n
The kanji that comprise \u9177\u6691 are \u9177 (hido[i]\/koku) and \u6691 (atsu[i]\/sho), the later meaning \u201chot\u201d and the former meaning \u201csevere,\u201d \u201charsh\u201d or \u201ccruel.\u201d This has led some overseas news outlets to translate \u9177\u6691\u65e5 (kokusho-bi) as a \u201ccruelly hot day.\u201d<\/p>\n
No less cruel is a \u731b\u6691\u65e5 (m\u014dshobi, very hot day). The \u6c17\u8c61\u5e81 defines a \u731b\u6691\u65e5 as a day when the \u6700\u9ad8\u6c17\u6e29 (saik\u014d kion, maximum temperature) reaches 35\u5ea6 (sanj\u016bgo-do, 35 C) or higher. In 2025, Tokyo recorded 25 \u731b\u6691\u65e5 and 69 additional \u771f\u590f\u65e5<\/a> (manatsubi, midsummer days) \u2014 when the temperature is 30\u5ea6 or higher. Nearby, Kofu, in Yamanashi Prefecture, experienced 53 \u731b\u6691\u65e5 and 73 \u771f\u590f\u65e5.<\/p>\n Another feature of the intense Japanese summer \u5929\u6c17 (tenki, weather) is the \u71b1\u5e2f\u591c (nettaiya, tropical night). On these nights, the \u6700\u4f4e\u6c17\u6e29 (saitei kion, minimum temperature) remains 25\u00b0C or higher. In 2025, Tokyo recorded 55 such nights<\/a>, while Nagoya, Osaka and Kobe recorded 73, 81 and 82, respectively.<\/p>\n With all this heat, you are more likely to hear warnings about \u71b1\u6ce2 (neppa, heat waves) and \u71b1\u4e2d\u75c7 (netch\u016bsh\u014d, heatstroke), including \u71b1\u4e2d\u75c7\u8b66\u6212\u30a2\u30e9\u30fc\u30c8 (netch\u016bsh\u014d keikai ar\u0101to, heatstroke alerts).<\/p>\n Where does this extreme heat come from? A number of atmospheric and oceanic \u73fe\u8c61 (gensh\u014d, phenomena) can contribute to Japan\u2019s increasingly extreme summers. Among them are \u30e9\u30cb\u30fc\u30cb\u30e3\u73fe\u8c61 (Ran\u012bnya gensh\u014d, La Ni\u00f1a), \u6b63\u306e\u30a4\u30f3\u30c9\u6d0b\u30c0\u30a4\u30dd\u30fc\u30eb\u30e2\u30fc\u30c9\u73fe\u8c61 (sei no Indo-y\u014d daip\u014dru m\u014ddo gensh\u014d, positive Indian Ocean Dipole) and the \u4e8c\u91cd\u9ad8\u6c17\u5727 (nij\u016b k\u014dkiatsu, double high-pressure system). The latter, in particular, can trap hot air over Japan and has contributed to causing \u9177\u6691\u65e5 in recent summers.<\/p>\n Many of these climate systems affect the entire \u65e5\u672c\u5217\u5cf6 (Nihon rett\u014d, Japanese archipelago), meaning there can be surprisingly little variation in summer temperatures from south to north when the heat waves arrive. On July 21 to 22, during the peak of a \u4e8c\u91cd\u9ad8\u6c17\u5727, Kagoshima and Sendai had the same daily highs<\/a> of 35.6<\/a> and 34.7\u5ea6<\/a> \u2014 despite the cities being roughly 1,200 kilometers apart as the crow flies, about the distance from Atlanta to New York or Rome to Berlin.<\/p>\n And it\u2019s not just the \u71b1 (netsu, heat) that causes problems, it\u2019s the \u6e7f\u5ea6 (shitsudo, humidity). The \u4f53\u611f\u6e29\u5ea6 (taikan ondo, perceived or \u201cfeels-like\u201d temperature) can be quite different from the actual \u6c17\u6e29 (kion, air temperature) because humidity affects how hot the body feels. Japan also uses the \u6691\u3055\u6307\u6570 (atsusa shis\u016b, heat stress index), a measure that takes temperature, humidity and radiant heat into account. This means that certain regions along Japan\u2019s coast, where \u6c17\u6e29 is lower but \u6e7f\u5ea6 is higher, can actually feel just as hot as a drier inland city. The aforementioned Kofu averages summer highs of 33.0\u5ea6 compared with 30.2\u5ea6 in seaside Atami, Shizuoka Prefecture, but the difference in humidity means Kofu\u2019s \u6691\u3055\u6307\u6570 is only one degree higher than Atami\u2019s, rather than three.<\/p>\n All of these factors mean that Japan\u2019s most extreme summer heat is found neither in the far south nor in the driest or wettest parts of the country. Instead, some of the hottest places are \u76c6\u5730 (bonchi, basins) such as Kofu and Tajimi in Gifu Prefecture. Surrounded by mountains, they are shielded from ocean breezes and trap heat. When wind does reach them, it can arrive already superheated after passing over big cities such as Tokyo and Nagoya.<\/p>\n \u3058\u3083\u3042\u3001\u3069\u3046\u3084\u3063\u305f\u3089\u3053\u306e\u6691\u3055\u304b\u3089\u9003\u3052\u3089\u308c\u308b\u306e\u3067\u3057\u3087\u3046\u304b\uff1f (J\u0101, d\u014d yattara kono atsusa kara nigerareru no desh\u014d ka?, So how can we escape from this heat?)<\/p>\n Moving from the \u76c6\u5730 to the \u6d77\u8fba (umibe, seaside) lowered the \u6691\u3055\u6307\u6570 (atsusa shis\u016b, heat stress index) by about one degree. Heading north to \u6771\u5317 (T\u014dhoku, the Tohoku region [where Sendai is located]) lowers it by about one more degree. How far north do we need to go?<\/p>\n In recent years, very far north indeed. Even in Aomori and Sapporo, summer temperatures can soar, with the heat index reaching uncomfortable levels. To find truly cooler conditions, you\u2019d practically have to go all the way to Wakkanai, Japan\u2019s northernmost city.<\/p>\n \u5168\u7136\u9003\u3052\u3089\u308c\u306a\u3044\u306e\u3067\u306f\u306a\u3044\u304b\uff1f\uff01 (Zenzen nigerarenai no dewa nai ka?!, Maybe we can\u2019t escape at all?!)<\/p>\n Not by fleeing north. There is a true way, a better way: \u4e0a\u3078 (ue e, upward).<\/p>\n \u6a19\u9ad8\u304c\u9ad8\u3051\u308c\u3070\u9ad8\u3044\u307b\u3069\u3001\u7a7a\u6c17\u306f\u51b7\u305f\u304f\u306a\u308b (Hy\u014dk\u014d ga takakereba takai hodo, k\u016bki wa tsumetaku naru, the higher the elevation, the cooler the air). This useful construction, \uff5e\u3070\uff5e\u307b\u3069, means \u201cthe more A, the more B.\u201d Another heat-related example would be, \u6c17\u6e29\u304c\u9ad8\u3051\u308c\u3070\u9ad8\u3044\u307b\u3069\u3001\u7720\u308a\u306b\u304f\u304f\u306a\u308b (Kion ga takakereba takai hodo, nemurinikuku naru, The hotter the temperature, the harder it is to sleep) or \u5916\u306b\u9577\u304f\u3044\u308c\u3070\u3044\u308b\u307b\u3069\u3001\u6c57\u3092\u304b\u304f (Soto ni ireba iru hodo, ase o kaku, The longer I stay outside, the more I sweat).<\/p>\n Even in Japan, the \u6a19\u9ad8 (hy\u014dk\u014d, elevation) effect is striking. \u6a19\u9ad8600\u30e1\u30fc\u30c8\u30eb\u306e\u677e\u672c\u5e02 (Hy\u014dk\u014d roppyaku m\u0113toru no Matsumoto-shi, Matsumoto City at 600 meters elevation) has recorded an \u6691\u3055\u6307\u6570 (atsusa shis\u016b, heat stress index) of 34 in recent summers. At \u6a19\u9ad81,000\u30e1\u30fc\u30c8\u30eb\u306e\u8efd\u4e95\u6ca2 (hy\u014dk\u014d sen m\u0113toru no Karuizawa, Karuizawa at 1,000 meters elevation), the figure is 29. And at \u6a19\u9ad81,400\u30e1\u30fc\u30c8\u30eb\u306e\u5965\u65e5\u5149 (hy\u014dk\u014d sen yonhyaku m\u0113toru no Oku-Nikk\u014d, Inner Nikko at 1,400 meters elevation), it falls to 24.<\/p>\n If you really want to escape the summer heat, head for the mountains. That may be one reason \u5c71\u767b\u308a (yamanobori, mountain climbing) and \u30cf\u30a4\u30ad\u30f3\u30b0 (haikingu, hiking) are such popular summer activities in Japan. Just be prepared: The heat may be less cruel on the mountain, but the trails can be.<\/p>\n","protected":false},"excerpt":{"rendered":"Is there any escaping Japan\u2019s summer \u9177\u6691 (kokusho, extreme heat)? 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