Japan: Land of Six Seasons (an overview of the climate of the archipelago)
Few visitors to Japan can imagine how extreme the climatic variation is around the country. As an example, just consider one day in February, let's take Valentine's Day, 14th February, as an example, on that day, you and your loved one could choose to: go snow-boarding in fabulous powder snow in the Niseko region of west Hokkaido, don dry-suits and frolic amongst sea-ice on the Sea of Okhotsk off northeast Hokkaido, or choose flippers and snorkels for a swim off a coral sand beach in Okinawa.
The climate of Japan hinges on a number of very significant factors: first, its location close to the large Asian continent; second its considerable length from northeast to southwest; third its range of altitudes from sea level to well over 3,000 m, and fourth, major oceanic currents (a significant cold current flows south past its northern shores, and a major warm current flows north past its southern shores, these mingling off eastern Honshu and forming a particularly rich marine zone).
Because of its location off the Asian continent, Japan is dominated, especially in winter by frigid air masses flowing off the continent and bringing extremes of severe weather that one might not otherwise expect at this latitude. Japan's great length, combined with its range of altitudes, mean that there is considerable climatic variation from north to south, such that it is sub-Arctic in the north and sub-tropical in the south, and from sea-level to mountain top.
In general, the climate in any given area of the country is distinctly seasonal. Although typically described in the travel literature as having four distinct seasons, it is not quite as simple as that. Count them for your self: following a warm dry spring, there is a prolonged rainy season (tsuyu), followed by a hot humid summer, a dramatic typhoon season, and a paint box coloured autumn; finally, there is a long, very cold winter, especially in the north. Count them again; Japan has six seasons.
Even describing a single one of these seasons can be difficult. For example, in Okinawa winter is barely cooler than summer and lasts only a month or so. In most of Japan, true winter lasts from December to February, however in Hokkaido, in the north, it stretches at least from November to March and snow pack remains heavy throughout much of April away from the lowlands and throughout May in the mountains.
Whereas the northern island of Hokkaido and the highlands of northern Honshu experience a decidedly more boreal climate with low temperatures and deep snow, at the other extreme the southern island of Kyushu and the island chain between Kyushu and Taiwan have cool to mild winters with no snow and long hot humid summers.
Rainfall in Japan
Rainfall is considerable during the approximately 40-day-long monsoon-like rainy season (tsuyu), when precipitation starts first in the south and moves north during May, June and July. Further heavy rains fall in September and October in association with the destructive tropical storms known as typhoons, although the first typhoons of the year may actually be reported from June onwards.
Autumn brings a riot of colours, with reddening rowans contrasting with Japanese Stone Pine; In severe winters, storm pushed ice piles up along the Sea of Okhotsk coast near Abashiri.
With frigid Arctic air blowing across Siberia prevailing winter winds are from the north-west, whereas prevailing summer winds are from the south-east, off the tropical Pacific, hence the Japanese archipelago experiences wide seasonal variation in temperatures and encompasses regions experiencing subarctic, temperate, and sub-tropical climates.
Currents, significantly affect coastal climate and hence the distribution of plants and animals and also agricultural crops. Japan benefits from having two important currents and several other minor currents. Year round a cold current, the Oyashio, flows down the northeast coast from the Bering Sea, and a warm current, the Kuroshio or Blackwater Current, washes its southwest shores flowing northwards from the south Pacific. Further branches of this current affect the western coast of Japan.
The presence of these currents affect: coastal temperatures (coastal fogs in summer are common off east Hokkaido, for example); the distribution of marine life and local fisheries; the distributions of many species of plans, including crops.
Japan's Climatic Zones
In addition to the overall annual calendar of the climate, Japan can be divided into climatic zones, each of which is characterised by a particular climate type. Considering the curving arms of the shape of the main islands of Japan as embracing the Sea of Japan, and reaching out to the Korean Peninsula in the south and Sakhalin in the north, the 'backbone' of this shape is provided by the ranges of mountains that stretch down through Hokkaido, Honshu and into Kyushu.
The region on the Sea of Japan side of these mountains experiences considerable winter precipitation, mostly in the form of snow in Honshu and Hokkaido, while on the Pacific Ocean side of these same mountains the winter climate tends to be colder, clearer and drier.
There is an additional layer of complexity to this simple divide in the climate between the Sea of Japan and the Pacific Ocean sides, because of the length of the archipelago. The northern part of the country falls into Japan's Northernmost Climatic Zone (i.e. the northern temperate or sub-boreal climate), dominated by long, cold winters and relatively cool summers.
The Japan Sea coast of northern and central Honshu is the Northwest Climatic Zone, dominated by long, relatively humid winters with heavy snowfalls, and by being cooler than the Pacific coast in summer.
The corresponding Pacific Ocean Climatic Zone is dry and cold in winter and hot in summer with a tendency to high humidity. Sandwiched between these two in the mountains and around them is the Central Highland Climatic Zone, with a more distinctly continental-type climate with low winter temperatures and high summer temperatures.
Further west, the region of the inland sea between western Honshu, Shikoku and northwest Kyushu lies within the Seto Inland Sea Climatic Zone, which experiences a Mediterranean-type climate with mild weather throughout the year. In the south, the islands of the old Ryukyu Kingdom fall within the Nansei Shoto Climatic Zone and experience a subtropical climate with year-round precipitation and characterized by mild or even warm winters and long hot humid summers.
During the winter the archipelago tends to be dominated by frigid air masses flowing southeastwards from the high-pressure areas that develop over Siberia towards the low pressure areas spawned over the northern Pacific, and these can bring severe conditions, with grey skies and heavy snowfalls to the mountains facing the Sea of Japan, and prolonged freezing and clear blue skies to areas facing the Pacific.
The arrival early in the year of Haru-ichiban, the first warm wind of spring, represents a turning point in this climatic system, bringing a distinct change in the weather and for the months ahead it will be dominated by warm tropical winds flowing northeastwards up the island chain bringing higher humidity and eventually the rainy season (tsuyu) and typhoons.
Consider that the nation's capital, Tokyo, at just above 35 is situated within the Pacific Ocean Climatic Zone and is typically cold to very cold in winter and hot and humid in winter.
Tokyo is on the same latitude as coastal North Carolina in the east of the USA, San Luis Obispo in California, or Tangier in Morocco, but experiences a very different climate.
Seasonal Change & Global Warming Effect in Japan
As the climate of Japan changes over time, winters are becoming shorter and milder, although temperatures continue to drop to below -30 at certain inland locations in Hokkaido in winter, with fewer of the prolonged blizzards down the Sea of Japan coast that used to isolate that region in winter, summers are becoming hotter (one the hottest temperatures recorded so far was of 40.9° Centigrade in Tajimi in Gifu Prefecture on 16 August 2007 followed by 41.0° Centigrade in Kochi, Shikoku in 2013), and more importantly summer nights are remaining warmer for longer, and throughout the year the weather is becoming more extreme and less predictable than in the past.