🇯🇵Japan

Japan spans 20°25′–45°33′N as an East Asian island nation (approximately 377,975 km²) comprising four main islands (Hokkaidō, Honshū, Shikoku, Kyūshū) plus the Ryūkyū chain (Okinawa) and roughly 14,000 smaller islands stretching 3,000 km north–south. Intensely volcanic and mountainous, the landscape features the Japanese Alps on Honshū, Mount Fuji (3,776 m, the highest peak), and active volcanoes like Sakurajima, Asama, and Aso.

This extraordinary topography produces a complete climate spectrum: humid continental (Dfb / Dfa) in Hokkaidō and northern Honshū with heavy sea-effect snow on the Sea-of-Japan coast, humid subtropical (Cfa) across most of central and southern Honshū, Shikoku, and Kyūshū, tropical rainforest (Af) in the southern Ryūkyūs, and alpine tundra (ET) on the highest Japanese Alps and Mount Fuji summit.

Tokyo has January highs of 10°C and lows of 1°C, and August highs of 31°C, with 1,530 mm rainfall and a marked tsuyu rainy season June–July plus the autumn typhoon season. Sapporo sees January highs around 0°C and lows of −6°C, and August highs of 26°C, with 1,150 mm and heavy sea-effect snow (approximately 4.8 m annually). Niigata on the Sea-of-Japan coast has January highs of 5°C and lows around 0°C, and August highs of 31°C, with 1,800 mm and about 1.4 m of snowfall a year.

Japan experiences major typhoons including Vera (September 1959, roughly 5,000 deaths), Tip (1979, the strongest tropical cyclone ever recorded), and Hagibis (October 2019). The July 2018 western Japan floods killed approximately 225 people, and August 2020 saw 41.1°C at Hamamatsu, equalling Japan's national record at the time.

Our archive covers 292 Japanese cities with daily ERA5 reanalysis data going back to 1940. The hottest July afternoons are in Ōita, with average highs around 31°C, while Obihiro has the coldest January nights, with average lows near −13.8°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 2°C.