UV Index Japan
According to the WHO, the average daily ambient ultraviolet radiation in Japan is 2,521 J/m² (joules per square metre).
UV radiation overview
Japan is an archipelago stretching roughly 3,000 km from north to south, spanning from about 24°N in the Okinawa islands to around 45.5°N in northern Hokkaido. The country comprises four main islands — Hokkaido, Honshu, Shikoku and Kyushu — together with the long Ryukyu chain extending into the subtropics. Terrain is overwhelmingly mountainous: Mt Fuji on Honshu rises to 3,776 m, and elevated central ranges shape regional climate. This wide latitudinal range and pronounced relief produce sharply contrasting UV environments across the islands.
A defining feature of Japan's UV climate is the contrast between subtropical Okinawa, where the UV index frequently reaches 11+ in summer and remains elevated through much of the year, and Hokkaido in the north, where peak UVI is more moderate. The Japan Meteorological Agency (JMA) runs long-term UV monitoring at four sites — Sapporo, Tsukuba, Naha and the remote Minamitorishima — providing the official national record of surface UV. The tsuyu (rainy season) cloud cover during early summer also strongly modulates UV doses across central and western Japan.
Japan sits at #150 of 191 in the WHO's global ambient-UV ranking with about 2,521 J/m² of average daily UV, around the 22nd percentile worldwide.
UV Radiation in Japan
This ranks 150 out of 191 countries measured worldwide — where 1 receives the most UV radiation.
Source: WHO Global Health Observatory (1997–2003)
