Geography and climate of Japan

Honshu, the largest island, holds Tokyo, Osaka, Nagoya and most of the population. Hokkaido in the north is the second largest and the least densely settled; Kyushu in the south-west and Shikoku, the smallest of the four, are separated from Honshu by narrow straits now crossed by tunnels and bridges. The Seto Inland Sea between Honshu, Shikoku and Kyushu is dotted with hundreds of islands.

South of Kyushu the Nansei (Ryukyu) Islands curve towards Taiwan, with Okinawa Island as their centre. Far out in the Pacific lie the Ogasawara (Bonin) Islands, and the country's southernmost and easternmost points, Okinotorishima and Minamitorishima, are tiny outposts. A recount by the Geospatial Information Authority in 2023 put the total number of islands at 14,125.

Roughly three quarters of Japan is mountainous or hilly. The highest ranges are the Japanese Alps in central Honshu – the Hida, Kiso and Akaishi mountains – with many peaks above 3,000 metres. East of them runs the Fossa Magna, a great rift across Honshu, along which rise volcanoes such as Yatsugatake and Mount Fuji.

Volcanoes line the country from Hokkaido to the southern islands; the Japan Meteorological Agency lists 111 active volcanoes. They shape the scenery of caldera lakes and plateaus and feed the thousands of hot springs, but also make eruptions part of the national hazard picture.

Japanese rivers are short and steep, falling quickly from the mountains to the sea, which makes them prone to floods after heavy rain. The Shinano, flowing through Nagano and Niigata into the Sea of Japan, is the longest; the Tone, which drains much of the Kanto region, has the largest basin. The Ishikari in Hokkaido and the Kiso in central Honshu are other major rivers.

The largest plains – the Kanto Plain around Tokyo, the Nobi Plain around Nagoya, the Osaka Plain and the Ishikari Plain around Sapporo – are home to the great cities. Lake Biwa in Shiga Prefecture, the largest lake, supplies water to the Kyoto–Osaka region; many other lakes, such as Towada, Shikotsu and Tazawa, fill volcanic calderas.

Most of Japan has a temperate climate with hot, humid summers and cool to cold winters, but the differences between regions are considerable. Meteorologists usually distinguish six zones, shaped by latitude, the mountain spine and the seasonal monsoon.

The contrast between the two sides of Honshu is especially marked in winter: while Tokyo and the Pacific coast see long spells of sunny, dry weather, the Sea of Japan coast lies under grey skies and heavy snow.

The Japanese attach great importance to the seasons, and they are unusually distinct. Spring brings the cherry blossom front, which moves from Okinawa in January and Kyushu in late March to Hokkaido in May. Summer is hot and humid, with the rainy season at its start and typhoons towards its end. Autumn, from late September, is generally dry and clear, with autumn colours travelling from the northern mountains southwards. Winter is dry and sunny on the Pacific side and snowy on the Sea of Japan side and in the mountains.

Many festivals, foods and customs follow this calendar, from cherry-blossom viewing to moon viewing and the New Year.

The rainy season, tsuyu or baiu, is caused by a stationary front between cool northern and warm southern air masses. It begins in Okinawa in May, reaches Kyushu, Shikoku and most of Honshu in early June and usually ends from mid to late July; Hokkaido is largely spared. Rain is frequent rather than constant, but the end of the season often brings intense downpours.

Typhoons form over the western Pacific, with around 25 in an average year. They affect Japan mainly from July to October, most often in August and September, and Okinawa and southern Kyushu are hit most frequently. Their wind, storm surge and rain can disrupt flights, trains and ferries for a day or more.

When cold Siberian air crosses the relatively warm Sea of Japan in winter, it picks up moisture and dumps it as snow on the mountains facing the coast. This makes the region from northern Honshu to Hokuriku one of the snowiest inhabited areas in the world, known as yukiguni, 'snow country', the title of Kawabata Yasunari's novel set in Niigata.

Heavy snow shapes local life and architecture, from the steep thatched roofs of Shirakawa-go to arcaded streets and snow-melting pipes in towns. It also creates the powder snow of Hokkaido and Nagano that draws skiers from around the world.