East Asian Rainy Season
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The East Asian rainy season (), also called the plum rain, is caused by
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
along a persistent stationary front known as the
Meiyu front The ''meiyu'' front, also known as ''baiu'' front, is a persistent nearly stationary weak baroclinic zone in the lower troposphere. It is located over the east coast of China and Taiwan at its western end, and over the Pacific Ocean south of Japa ...
for nearly two months during the late spring and early summer in
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
between mainland
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
,
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
,
Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, Northern
Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...
, the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
, and the
Russian Far East The Russian Far East (russian: Дальний Восток России, r=Dal'niy Vostok Rossii, p=ˈdalʲnʲɪj vɐˈstok rɐˈsʲiɪ) is a region in Northeast Asia. It is the easternmost part of Russia and the Asian continent; and is admini ...
. The
wet season The wet season (sometimes called the Rainy season) is the time of year when most of a region's average annual rainfall occurs. It is the time of year where the majority of a country's or region's annual precipitation occurs. Generally, the sea ...
ends during the summer when the
subtropical ridge The horse latitudes are the latitudes about 30 degrees north and south of the Equator. They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as Subtropics, subtropical ridges, or highs. It is a h ...
becomes strong enough to push this front north of the region. These weather systems can produce heavy rainfall and flooding.


Etymology

In China, the term "plum rain" was used for the rain in the fourth and fifth lunar month.Lu Dian's ''
Piya The ''Piya'' (; "Increased ra") was a Chinese dictionary compiled by Song Dynasty scholar Lu Dian ( 陸佃/陆佃, 1042-1102). He wrote this ''Erya'' supplement along with his ''Erya Xinyi'' (爾雅新義 "New Exegesis of the ''Erya''") comment ...
'' (published in the Song dynasty). Cited in
It specifically refers to the historical belief that, when the
plums A plum is a fruit of some species in ''Prunus'' subg. ''Prunus'.'' Dried plums are called prunes. History Plums may have been one of the first fruits domesticated by humans. Three of the most abundantly cultivated species are not found i ...
turn yellow and fall at the south of the
Yangtze The Yangtze or Yangzi ( or ; ) is the longest river in Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flows ...
in the fourth and fifth months, the moisture that evaporates from the plant turns into rain. The term appears in the following poem by
Du Fu Du Fu (; 712–770) was a Tang dynasty poet and politician. Along with his elder contemporary and friend Li Bai (Li Po), he is frequently called the greatest of the Chinese poets.Ebrey, 103. His greatest ambition was to serve his country as ...
(fl. 8th century) of the
Tang dynasty The Tang dynasty (, ; zh, t= ), or Tang Empire, was an Dynasties in Chinese history, imperial dynasty of China that ruled from 618 to 907 AD, with an Zhou dynasty (690–705), interregnum between 690 and 705. It was preceded by the Sui dyn ...
: Japan later adapted and transliterated the Chinese term "plum rain" to call the rainy season . The season is instead commonly called ''Jangma'' (장마) in Korea, which means "long rain". The term was originally spelled ''Dyangmah'' (댱마ㅎ) in 1500s, which was the mix of the
hanja Hanja (Hangul: ; Hanja: , ), alternatively known as Hancha, are Chinese characters () used in the writing of Korean. Hanja was used as early as the Gojoseon period, the first ever Korean kingdom. (, ) refers to Sino-Korean vocabulary, wh ...
character 長 ("long") and the old native Korean word 마ㅎ (''mah'', "rain"). The word Dyangmah eventually transformed from ''Jyangma'' (쟝마) in 1700s to the current form of ''Jangma'' after 1900s.


Formation

An east-west zone of disturbed weather during spring along this front stretches from the east China coast, initially across Taiwan and Okinawa, later, when it has shifted to the north, eastward into the southern peninsula of South Korea and Japan. The rainy season usually lasts from May to June in Taiwan and
Okinawa is a prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 km2 (880 sq mi). Naha is the capital and largest city ...
, from June to July (approximately 50 days) in Russian
Primorsky Krai Primorsky Krai (russian: Приморский край, r=Primorsky kray, p=prʲɪˈmorskʲɪj kraj), informally known as Primorye (, ), is a federal subject (a krai) of Russia, located in the Far East region of the country and is a part of the ...
, Japan and Korea and from July to August in eastern China (especially the
Yangtze The Yangtze or Yangzi ( or ; ) is the longest river in Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flows ...
and
Huai River The Huai River (), Postal Map Romanization, formerly romanization of Chinese, romanized as the Hwai, is a major river in China. It is located about midway between the Yellow River and Yangtze, the two longest rivers and largest drainage basins ...
regions). The weather front forms when the moist air over the Pacific meets the cooler continental
air mass In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to la ...
. The front and the formation of frontal depressions along it brings precipitation to Primorsky Krai, Japan, Korea, eastern China, and Taiwan. As the front moves back and forth depending on the strength of cool and warm air masses, there is often prolonged precipitation and sometimes flooding in eastern
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
. However, in the years that it does not rain as much as usual, a drought might result. The rainy season ends when the warm air mass associated with the subtropical ridge is strong enough to push the front north and away.


Effects

The high
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...
in the air during this season encourages the formation of
mold A mold () or mould () is one of the structures certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal seco ...
and rot not only on food but on fabrics as well. Environmentally, heavy rains encourage
mudslides A mudflow or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...
and flooding in all areas affected. The most rain in a one-hour period as recorded in Japan was in
Nagasaki is the capital and the largest city of Nagasaki Prefecture on the island of Kyushu in Japan. It became the sole port used for trade with the Portuguese and Dutch during the 16th through 19th centuries. The Hidden Christian Sites in the ...
in 1982 with . The highest overall recorded rainfall during the rainy season in Japan was in 2003 when
Miyazaki Prefecture is a prefecture of Japan located on the island of Kyūshū. Miyazaki Prefecture has a population of 1,073,054 (1 June 2019) and has a geographic area of 7,735 km2 (2,986 sq mi). Miyazaki Prefecture borders Ōita Prefecture to the north, Kuma ...
recorded rains of .


Japan

In Japan, the rainy season is called , and lasts from early June to mid-July in most of the country (
Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island separ ...
,
Kyushu is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surroun ...
and
Shikoku is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), '' ...
), approximately June 7 to July 20 in the
Kansai The or the , lies in the southern-central region of Japan's main island Honshu, Honshū. The region includes the Prefectures of Japan, prefectures of Nara Prefecture, Nara, Wakayama Prefecture, Wakayama, Kyoto Prefecture, Kyoto, Osaka Prefectur ...
and Kantō regions in Honshū.Rainy Season (Tsuyu)
japan-guide.com
The season is roughly a month earlier (early May through mid-June) in
Okinawa is a prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 km2 (880 sq mi). Naha is the capital and largest city ...
(the southernmost region of the country). There is no pronounced season in
Hokkaidō is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...
(the northernmost region of the country) because the front usually attenuates before it reaches the region so that it cannot produce the abundant rainfall. is also known as . The pop artist
Eiichi Ohtaki Eiichi Ohtaki (July 28, 1948 – December 30, 2013) was a Japanese musician, singer-songwriter and record producer. He first became known as a member of the rock band Happy End, but was better known for his solo work which began in 1972. ...
produced a popular song by this name, and a WW2 Japanese naval ship was also given this name. The rains in the middle of November - early December are sometimes called the , literally "rainy season of the
camellia ''Camellia'' (pronounced or ) is a genus of flowering plants in the family Theaceae. They are found in eastern and southern Asia, from the Himalayas east to Japan and Indonesia. There are more than 220 described species, with some controversy ...
" on account of the timing with the blossoming of the seasonal flower. This period is generally avoided for tourism, but some sights are considered particularly atmospheric in the rain and fog, particularly mountain forests, notably
Sacred Sites and Pilgrimage Routes in the Kii Mountain Range Sacred Sites and Pilgrimage Routes in the Kii Mountain Range is a UNESCO World Heritage Site located on the Kii Peninsula in Japan. Selection criteria The locations and paths for this heritage site were based on their historical and modern imp ...
(including
Mount Kōya is a large temple settlement in Wakayama Prefecture, Japan to the south of Osaka. In the strictest sense, ''Mount Kōya'' is the mountain name ( sangō) of Kongōbu-ji Temple, the ecclesiastical headquarters of the Kōyasan sect of Shingon Budd ...
). Vegetation, especially moss, is also rather lush at this time, and hence sights known for their moss, such as Saihō-ji (the moss temple) are also popular at this time of year.


Korea

The rainy season is between June and mid-July. It is caused by hot and humid high pressure forming in the
Sea of Okhotsk The Sea of Okhotsk ( rus, Охо́тское мо́ре, Ohótskoye móre ; ja, オホーツク海, Ohōtsuku-kai) is a marginal sea of the western Pacific Ocean. It is located between Russia's Kamchatka Peninsula on the east, the Kuril Islands ...
due to the North Pacific anticyclone combining with Asiatic continental high pressure. When the two meteorological events meet they form a long (, from 장마 "rainy season" and 전선 "weather front"). Beginning in late-May, the North Pacific high pressure forces the weaker continental anticyclone south of
Okinawa Island is the largest of the Okinawa Islands and the Ryukyu (''Nansei'') Islands of Japan in the Kyushu region. It is the smallest and least populated of the five main islands of Japan. The island is approximately long, an average wide, and has an ...
. This fall to the south then reverses and gradually strengthens as it moves northwards back towards the Korean peninsula. On landfall, heavy monsoon rains lead to torrential downpours and flooding. By August the system has weakened as the southern systems retreat towards the Philippine archipelago. By early autumn, the North Pacific high-pressure system is pushed away as Asiatic continental cold high pressure moves southwards. This produces inclement weather although not on the scale of the summer monsoons. Korea can, however, be struck by typhoons during this period.


Timing

In some years, the rainy season's actual beginning and end are under debate. For example, in 2005, the subtropical ridge moved quickly northward in late June/early July. The weather front skipped the
Yangtze The Yangtze or Yangzi ( or ; ) is the longest river in Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flows ...
region and there was no rainy season there. Then, the ridge retreated southward and there was significant rainfall in the region. This gave rise to the question of whether this was the summer-type rainfall pattern that is common after the first rainy season or the second rainy season. Some
meteorologist A meteorologist is a scientist who studies and works in the field of meteorology aiming to understand or predict Earth's atmospheric phenomena including the weather. Those who study meteorological phenomena are meteorologists in research, while t ...
s even argued that the rainy period in late June was not a true rainy season.


See also

* East Asian Monsoon *
Meiyu front The ''meiyu'' front, also known as ''baiu'' front, is a persistent nearly stationary weak baroclinic zone in the lower troposphere. It is located over the east coast of China and Taiwan at its western end, and over the Pacific Ocean south of Japa ...
*
List of China-related topics The following outline is provided as an overview of and topical guide to China: The People's Republic of China is the most extensive country in East Asia and the third most extensive country in the world. With a population of over 1,400,000 ...
* List of Japan-related topics *
List of Taiwan related topics The following outline is provided as an overview of and topical guide to Taiwan: Taiwan – a country in East Asia, officially named the Republic of China (ROC). Originally based in mainland China, the ROC now governs the island of Ta ...


References

{{Seasons Environment of East Asia Climate of China Climate of Taiwan Climate of North Korea Climate of South Korea Climate of Japan Precipitation Rain Summer Tropical meteorology Kigo