Physical Framework and the Climate of Japan

Physical Framework:

Physically, the two overwhelming aspects of Japan are its mountains and its insularity. Land and water are so close to each other that one is always within sight of mountains and seas. The Japanese word for landscape or scen­ery is sansui from the two characters for “mountain” and “water”.

Two-thirds of the country is mountainous, and less than one-fourth is level enough for agriculture, and only 12.5 percent of the total land sur­face is under cultivation. The mountains are for the most part fairly “young” in an early stage of dissection in which steep slopes predominate, and there is a dense network of steep-sided river valleys.

Within the rugged mountainous framework there are 200 volcanoes, one- third of which have been active within historic times. Fujiyama is the most fa­mous of the active peaks, although it has not erupted since the early 18th century. It is 12,388 feet (3,776 meters) high, and has a symmetrical cone which reaches 37 de­grees toward the summit.

Many of the Japanese volcanoes are conical in shape and contain calderas or circular-shaped de­pressions occupied by lakes. Several volcanoes are active and given to frequent, and violent eruptions. More than 1,000 hot springs in the country are associated to volcanic intrusions, although some owe their temperatures to friction along fault zones. Health resorts are developed around several hot springs.

Earthquakes are common throughout the country which receives about 1,500 shocks of varying intensity a year. The de­structive ones occur once in three years on the average, affecting only smaller areas. Much of Japan’s coastline is indented, more on the Pacific side than on the Sea of Japan. Much of the Pacific coast thus con­tains embayment’s and coves, providing a number of harbors. The Inland Sea be­tween the southwestern coast of Honshu Island and the northern coast of Kyushu and Shikoku, itself may be considered one large harbor containing several lesser har­bors lining its shores.

The coasts of southern Honshu and western Kyushu are dotted with natural harbors on which hun­dreds of fishing villages are located. The coastline along the Sea of Japan is rela­tively smooth with fewer areas of natural harbors. The coasts of Hokkaido are also mostly regular.

The mountains are divided into many small land blocks, separated by generally small lowlands and deep valleys; there is no long or continuous mountain range. These land blocks have resulted from in­tense faulting (movement of adjacent rock masses along a fracture) and warping (fold­ing).

Most streams are short, swift, and torrential, and are in their youthful stage. They have not had time to erode very far to build up extensive flood plains or deltas, but when the swift-flowing streams reach the sea, they carry with them fine material that might otherwise be deposited on the land.

The country has no large plains. Level land is limited to a few alluvial flood plains and deltas, and the dissected terraces of streams. Most of the flat land is located around the coast, and is broken up by local mountain barriers into isolated plains. The four main islands contain three dozen ar­eas large enough to be identified as lowlands.

The largest of these, and by far the most important in economic terms, is the Kanto Plain with an area of 2,500 sq. miles (6,475 sq. km) in eastern Honshu. It accommodates a quarter of the population of Japan and two of its largest cities, To­kyo and Yokohama. Other plains to the west of the Kanto include the Nobi Plain in east central Honshu, and the Kinki Plain at the eastern end of the Inland Sea.

To the north the larger plains, are located around Sendai (northeastern Honshu) and on Hokkaido the Ishikari lowland. It is noteworthy that each of these major plains is located on the Pacific side of the country; by comparison, larger plains, are few in number on the regular coast along the Japan Sea, the most prominent being the Niigata Plain.

A good deal of Japan’s surface is cov­ered by volcanic ash and lava, and river alluvium, and hence the soils of many of the coastal plains as well as the uplands, are derived from this source. Unfortunately most soils tend to be thin, immature, and are not very fertile, except those of the thicker alluvial deposits on the larger few lowlands identified above. Their light po­rous structure also makes them to be vulnerable to serious erosion, and makes irrigation more difficult.

Climate:

In general, the climate of Japan IS distinguished by its humidity and marked seasonal changes, and is mostly free from the disastrous fluctuations char­acteristic of India or northern China. For most part the entire country receives am­ple rainfall and generally enjoys a favorable climate.

No part of the country is too cold for agriculture except the north­ernmost part in Hokkaido which is climatically marginal for cultivation pri­marily reflecting its very cold winters where the frost-free season lasts 140 days as compared to 300 days in most of southern Japan. Japan is warmer than parts of northern China to the west in the same latitudes. It is located off the east coast of a large landmass, and continental influences are tempered by marine conditions.

Broadly speaking, Japan’s climate is monsoonal and governed by seasonal winds. The main influences affecting its cli­mate are the country’s latitudinal extent, the surrounding oceans, its proximity to the Asian landmass while local variations are related to variations in altitude and as­pect, and to the distribution of ocean cur­rents in the waters surrounding Japan. The broad features of Japan’s climate are con­sistent from year to year, but there can be marked variations over comparatively short distances.

The key climatic determinant is the in­teraction between the sea and the land, resulting in the monsoonal pattern of air j streams. In winter the country is under the influence of the predominantly westerly and northwesterly winds that blow from the northern interior of Asia, and bring cold, dry, polar continental air over the ar­chipelago.

Thus, the Japanese winters are comparatively much drier than the sum­mers. Precipitation in Osaka, for example, is three times in the three summer months than in the winter. No part of Japan is dry, however, and there is no true dry season. The northwestern monsoon winds that traverse the Japan Sea before reaching the islands pick up moisture and bring precipi­tation in the form of rain or snowfall to the area facing the Sea of Japan.

In summer, there is a reversal of wind direction. They are southeasterly and bring warm, moist air from the adjoining Pacific Ocean. The summer rainy season brings copious precipitation. Although the precipitation varies with topography, but most of the country receives more than 40 inches (1,020 millimeters) annually mainly during the summer.

The smallest amounts of precipitation occur on eastern Hok­kaido (30 to 40 inches) which is near the northern limits of the maritime air; the eastern Inland Sea and north-central high­lands of Honshu; both areas are protected in all directions by Coast Mountains.

Japan’s insularity also markedly affects the climatic pattern. The southern and southeastern coasts are washed by a warm Kuroshio ocean current moving north­eastward from the South China Sea to as far north as latitude 35° which has an aver­age minimum winter temperature of 68°F (20°C), and warms the coast of southern Kyushu, Shikoku, and Honshu to about the latitude of Tokyo.

A branch of the Kuroshio, the Tsushima current, moves westward along the Japan Sea, but its influ­ence is less than that of the parent stream. Conversely, a cold current, known as the Oyashio, moves southward from the Ber­ing Sea, cooling the northeastern coast of Honshu until it meets the waters of the Kuroshio, causing dense fogs in summers, particularly off Hokkaido, as noted earlier, the Sea of Japan acts an important climatic influence, especially in winter. The Sea of Japan side of Japan, therefore, is an area of copious precipitation all the year round, but with a marked winter, rather than a summer maximum.

Another characteristic feature of Ja­pan’s climate is the occurrence of violent storms or typhoons that invade southern sections of the country, averaging three to four each year during summer, especially in late August and September. These vio­lent storms originate throughout the year in tropical latitudes of the Pacific, but by August their tracks swing to the south of the Japanese archipelago, striking the west coast of Kyushu, southern coast of Shik­oku and southern part of the Kanto Plain. Often high winds and heavy downpours associated with the storms cause enormous damage whenever they strike land.

As regards temperature conditions, clearly the major determinants are the lati­tudes, and the local relief within the country. Obviously the southern parts of the country are generally warmer than the northern ones. The transitional seasons of spring and fall are shorter in the north.

At Asahikawa in the central part of the north­ern island of Hokkaido the mean temperature in January, the coldest month, is 16°F (-9°C) and in August, the hottest month is 70°F (21°C), with an aver­age temperature of 43°F (6°C). At Tokyo the mean temperature in January is 39°F (4°C), the mean temperature in August 81°F (27°C) and the average 59°F (15°C). The warmest temperatures occur on Kyushu, and the southern islands.

At Kagoshima, the mean for January is 45°F (7°C), and 81°F (27°C) for August, and the average is 63°F (17°C). Variations in tem­peratures (and climate in general) are also caused by the disposition of local relief fea­tures. In general, the mountainous backbone of the country interrupts air flow from northwest and southeast that cause heavy snows during winter along the Sea of Japan.

The western mountain slopes of Honshu also act as a major topographic barrier for the cold, winter winds they emanate from the Asian landmass, after these have crossed the Sea of Japan, pro­tecting the eastern coast of Honshu from the cold winds from the west.