Geography of Japan - Climate

Climate

Japan belongs to the temperate zone with four distinct seasons, but its climate varies from cool temperate in the north to subtropical in the south. Two primary factors influence Japan's climate: a location near the Asian continent and the existence of major oceanic currents. Two major ocean currents affect Japan: the warm Kuroshio Current (Black Current; also known as the Japan Current); and the cold Oyashio Current (Parent Current; also known as the Okhotsk Current). The Kuroshio Current flows northward on the Pacific side of Japan and warms areas as far north as Tokyo; a small branch, the Tsushima Current, flows up the Sea of Japan side. The Oyashio Current, which abounds in plankton beneficial to coldwater fish, flows southward along the northern Pacific, cooling adjacent coastal areas. The meeting point of these currents at 36 north latitude is a bountiful fishing ground.

Its varied geographical features divide Japan into six principal climatic zones.

• Hokkaidō (北海道, Hokkaidō?): Belonging to the humid continental climate, Hokkaidō has long, cold winters and cool summers. Precipitation is not great.

• Sea of Japan (日本海, Nihonkai?): The northwest seasonal wind in winter gives heavy snowfalls, which south of Aomori mostly melt before the end of winter. In summer it is a little less rainy than the Pacific area but sometimes experiences extreme high temperatures due to the foehn wind phenomenon.

• Central Highland (中央高地, Chūō-kōchi?): A typical inland climate gives large temperature differences between summers and winters and between days and nights. Precipitation is lower than on the coast due to rain shadow effects.

• Seto Inland Sea (瀬戸内海, Setonaikai?): The mountains in the Chūgoku and Shikoku regions block the seasonal winds and bring mild climate and many fine days throughout the year.

• Pacific Ocean (太平洋, Taiheiyō?): Winters are cold, with little snowfall, and summers are hot and humid due to the southeast seasonal wind. Precipitation is very heavy in the south, and heavy in the summer in the north.

• Ryukyu Islands (南西諸島, Nansei-shotō?): This zone has a subtropical climate with warm winters and hot summers. Precipitation is very high, and is especially affected by the rainy season and typhoons.

Japan is generally a rainy country with high humidity. Because of its wide range of latitude and seasonal winds, Japan has a variety of climates, with a latitude range often compared to that of the east coast of North America, from Nova Scotia to the U.S. state of Georgia. Tokyo is at about 35 degrees north latitude, comparable to that of Tehran, Athens, or Las Vegas. Regional climatic variations range from humid continental in the northern island of Hokkaido extending down through Northern Japan to the Central Highland, then blending with and eventually changing to a humid subtropical climate on the Pacific Coast and ultimately bordering very closely with a tropical climate on the Ryukyu Islands. Climate also varies dramatically with altitude and with location on the Pacific Ocean or on the Sea of Japan. Northern Japan has warm summers but long, cold winters with heavy snow. Central Japan in its elevated position, has hot, humid summers and moderate to short winters with some areas having very heavy snow, and southwestern Japan has long, hot, humid summers and mild winters. The generally humid, temperate climate exhibits marked seasonal variation such as the blooming of the spring cherry blossoms, the calls of the summer cicada and fall foliage colors that are celebrated in art and literature

The climate from June to September is marked by hot, wet weather brought by tropical airflows from the Pacific Ocean and Southeast Asia. These airflows are full of moisture and deposit substantial amounts of rain when they reach land. There is a marked rainy season, beginning in early June and continuing for about a month. It is followed by hot, sticky weather. Five or six typhoons pass over or near Japan every year from early August to early September, sometimes resulting in significant damage. Annual precipitation averages between 1,000 and 2,500 mm (40 and 100 in) except in the hyperhumid Kii Peninsula where it can reach 4,000 millimetres (160 in), which is the highest rainfall in subtropical latitudes in the world. Maximum precipitation, like the rest of East Asia, occurs in the summer months except on the Sea of Japan coast where strong northerly winds produce a maximum in late autumn and early winter. However, except for a few sheltered inland valleys during December and January, precipitation in Japan is above 25 millimetres (1 in) of rainfall equivalent in all months of the year, and in the wettest coastal areas it is above 100 millimetres (4 in) per month throughout the year.

In winter, the Siberian High develops over the Eurasian land mass and the Aleutian Low develops over the northern Pacific Ocean. The result is a flow of cold air southeastward across Japan that brings freezing temperatures and heavy snowfalls to the central mountain ranges facing the Sea of Japan, but clear skies to areas fronting on the Pacific.

Late June and early July are a rainy season—except in Hokkaidō—as a seasonal rain front or baiu zensen (梅雨前線?) stays above Japan. In summer and early autumn, typhoons, grown from tropical depressions generated near the equator, attack Japan with furious rainstorms.

The warmest winter temperatures are found in the Nanpō and Bonin Islands, which enjoy a tropical climate due to the combination of latitude, distance from the Asian mainland, and warming effect of winds from the Kuroshio, as well as the Volcano Islands (at the latitude of the southernmost of the Ryukyu Islands, 24° N). The coolest summer temperatures are found on the northeastern coast of Hokkaidō in Kushiro and Nemuro Subprefectures.

Sunshine, in accordance with Japan’s uniformly heavy rainfall, is generally modest in quantity, though no part of Japan receives the consistently gloomy fogs that envelope the Sichuan Basin or Taipei. Amounts range from about 6 hours per day in the Inland Sea coast and sheltered parts of the Pacific Coast and Kantō Plain to 4 hours per day on the Sea of Japan coast of Hokkaidō. In December there is a very pronounced sunshine gradient between the Sea of Japan and Pacific coasts, the former side can receive less than 30 hours and the Pacific side as much as 180 hours. In summer, however, sunshine hours are lowest on exposed parts of the Pacific coast where fogs from the Oyashio current create persistent cloud similar to that found on the Kuril Islands and Sakhalin.

As an island nation, Japan has a long coastline. A few prefectures are landlocked: Gunma, Tochigi, Saitama, Nagano, Yamanashi, Gifu, Shiga, and Nara. As Mt. Fuji and the coastal Japanese Alps provide a rain shadow, Nagano and Yamashi Prefectures have the least precipitation in Honshū, though this still exceeds 900 millimetres (35 in) annually. A similar effect is found in Hokkaidō, where Okhotsk Subprefecture receives as little as 750 millimetres (30 in) per year. All other prefectures have coasts on the Pacific Ocean, Sea of Japan, Seto Inland Sea or have a body of salt water connected to them. Two prefectures—Hokkaidō and Okinawa—are composed entirely of islands.

The hottest temperature ever measured in Japan, 40.9 °C (105.6 °F), occurred in Tajimi, Gifu on August 16, 2007.