Is there any escaping Âé¶¹´«Ã½ summer ¿áÊî (kokusho, extreme heat)?
In April, the šÝÏóŽØ (°ì¾±²õ³ó¨³¦³ó¨, Japan Meteorological Agency) released a bulletin titled ×î¸ßšÝΤ¬40¶ÈÒÔÉϤÎÈÕ¤ÎÃû³Æ¤ò¡¸¿áÊîÈÕ¡¹¤Ë›Q¶¨ (Saik¨ kion ga yonj¨±-do ij¨ no hi no meish¨ o ¡°kokusho-bi¡± ni kettei, The name ¡°intense heat day¡± has been officially adopted for days when the maximum temperature reaches 40 degrees Celsius or higher).
The kanji that comprise ¿áÊî are ¿á (hido[i]/koku) and Êî (atsu[i]/sho), the later meaning ¡°hot¡± and the former meaning ¡°severe,¡± ¡°harsh¡± or ¡°cruel.¡± This has led some overseas news outlets to translate ¿áÊîÈÕ (kokusho-bi) as a ¡°cruelly hot day.¡±
No less cruel is a ÃÍÊîÈÕ (³¾¨²õ³ó´Ç²ú¾±, very hot day). The šÝÏóŽØ defines a ÃÍÊîÈÕ as a day when the ×î¸ßšÝΠ(saik¨ kion, maximum temperature) reaches 35¶È (²õ²¹²ÔÂᨱ²µ´Ç-»å´Ç, 35 C) or higher. In 2025, Tokyo recorded (manatsubi, midsummer days) ¡ª when the temperature is 30¶È or higher. Nearby, Kofu, in Yamanashi Prefecture, experienced 53 ÃÍÊîÈÕ and 73 ÕæÏÄÈÕ.
Another feature of the intense Japanese summer ÌìšÝ (tenki, weather) is the ŸáŽ¡Ò¹ (nettaiya, tropical night). On these nights, the ×îµÍšÝΠ(saitei kion, minimum temperature) remains 25¡ãC or higher. In 2025, , while Nagoya, Osaka and Kobe recorded 73, 81 and 82, respectively.
With all this heat, you are more likely to hear warnings about Ÿá²¨ (neppa, heat waves) and ŸáÖÐÖ¢ (²Ô±ð³Ù³¦³ó¨±²õ³ó¨, heatstroke), including ŸáÖÐÖ¢¾¯½ä¥¢¥é©`¥È (²Ô±ð³Ù³¦³ó¨±²õ³ó¨ keikai ar¨¡to, heatstroke alerts).
Where does this extreme heat come from? A number of atmospheric and oceanic ¬FÏó (²µ±ð²Ô²õ³ó¨, phenomena) can contribute to Âé¶¹´«Ã½ increasingly extreme summers. Among them are ¥é¥Ë©`¥Ë¥ã¬FÏó (Ran¨©nya ²µ±ð²Ô²õ³ó¨, La Ni?a), Õý¤Î¥¤¥ó¥ÉÑó¥À¥¤¥Ý©`¥ë¥â©`¥É¬FÏó (sei no Indo-y¨ daip¨ru m¨do ²µ±ð²Ô²õ³ó¨, positive Indian Ocean Dipole) and the ¶þÖØ¸ßšÝˆR (nij¨± k¨kiatsu, double high-pressure system). The latter, in particular, can trap hot air over Japan and has contributed to causing ¿áÊîÈÕ in recent summers.
Many of these climate systems affect the entire ÈÕ±¾ÁÐu (Nihon rett¨, 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 ¶þÖØ¸ßšÝˆR, of and ¡ª 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.
And it¡¯s not just the Ÿá (netsu, heat) that causes problems, it¡¯s the ʪ¶È (shitsudo, humidity). The Ìå¸ÐÎÂ¶È (taikan ondo, perceived or ¡°feels-like¡± temperature) can be quite different from the actual šÝΠ(kion, air temperature) because humidity affects how hot the body feels. Japan also uses the ÊָÊý (atsusa shis¨±, heat stress index), a measure that takes temperature, humidity and radiant heat into account. This means that certain regions along Âé¶¹´«Ã½ coast, where šÝΠis lower but ʪ¶È is higher, can actually feel just as hot as a drier inland city. The aforementioned Kofu averages summer highs of 33.0¶È compared with 30.2¶È in seaside Atami, Shizuoka Prefecture, but the difference in humidity means Kofu¡¯s ÊָÊý is only one degree higher than Atami¡¯s, rather than three.
All of these factors mean that Âé¶¹´«Ã½ 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 ÅèµØ (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.
¤¸¤ã¤¢¡¢¤É¤¦¤ä¤Ã¤¿¤é¤³¤ÎÊ¤«¤éÌÓ¤²¤é¤ì¤ë¤Î¤Ç¤·¤ç¤¦¤«£¿ (J¨¡, d¨ yattara kono atsusa kara nigerareru no desh¨ ka?, So how can we escape from this heat?)
Moving from the ÅèµØ to the º£Þx (umibe, seaside) lowered the ÊָÊý (atsusa shis¨±, heat stress index) by about one degree. Heading north to –|±± (°Õ¨³ó´Ç°ì³Ü, the Tohoku region [where Sendai is located]) lowers it by about one more degree. How far north do we need to go?
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¡¯d practically have to go all the way to Wakkanai, Âé¶¹´«Ã½ northernmost city.
ȫȻÌÓ¤²¤é¤ì¤Ê¤¤¤Î¤Ç¤Ï¤Ê¤¤¤«£¿£¡ (Zenzen nigerarenai no dewa nai ka?!, Maybe we can¡¯t escape at all?!)
Not by fleeing north. There is a true way, a better way: ÉÏ¤Ø (ue e, upward).
˜Ë¸ß¤¬¸ß¤±¤ì¤Ð¸ß¤¤¤Û¤É¡¢¿ÕšÝ¤ÏÀ䤿¤¯¤Ê¤ë (Hy¨k¨ ga takakereba takai hodo, k¨±ki wa tsumetaku naru, the higher the elevation, the cooler the air). This useful construction, ¡«¤Ð¡«¤Û¤É, means ¡°the more A, the more B.¡± Another heat-related example would be, šÝΤ¬¸ß¤±¤ì¤Ð¸ß¤¤¤Û¤É¡¢Ãߤê¤Ë¤¯¤¯¤Ê¤ë (Kion ga takakereba takai hodo, nemurinikuku naru, The hotter the temperature, the harder it is to sleep) or Íâ¤ËéL¤¯¤¤¤ì¤Ð¤¤¤ë¤Û¤É¡¢º¹¤ò¤«¤¯ (Soto ni ireba iru hodo, ase o kaku, The longer I stay outside, the more I sweat).
Even in Japan, the ˜Ë¸ß (³ó²â¨°ì¨, elevation) effect is striking. ˜Ë¸ß600¥á©`¥È¥ë¤ÎËɱ¾ÊÐ (Hy¨k¨ roppyaku m¨¥toru no Matsumoto-shi, Matsumoto City at 600 meters elevation) has recorded an ÊָÊý (atsusa shis¨±, heat stress index) of 34 in recent summers. At ˜Ë¸ß1,000¥á©`¥È¥ë¤ÎÝX¾®›g (³ó²â¨°ì¨ sen m¨¥toru no Karuizawa, Karuizawa at 1,000 meters elevation), the figure is 29. And at ˜Ë¸ß1,400¥á©`¥È¥ë¤Î°ÂÈÕ¹â (³ó²â¨°ì¨ sen yonhyaku m¨¥toru no Oku-Nikk¨, Inner Nikko at 1,400 meters elevation), it falls to 24.
If you really want to escape the summer heat, head for the mountains. That may be one reason ɽµÇ¤ê (yamanobori, mountain climbing) and ¥Ï¥¤¥¥ó¥° (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.
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