GK:1.3.3 Precipitation
Geography of Korea: I. Natural Environment > 3. Climate > 3) Precipitation
목차
3) Precipitation
(1) Average Mean Rainfall
The Korean Peninsula receives less annual precipitation relative to neighboring Japan but rather more than such countries as the United States and France. From a global perspective the Korean Peninsula may be categorized as a high precipitation area. The areas that receive the most rainfall are Jeju Island and southern coastal areas. The area with the most annual precipitation is Geoje in Gyeongsangnam-do province, with over 2000mm annually, while Seongsan and Seogwipo on Jeju Island each receive over 1900mm. The areas with the least annual precipitation are Kaema Plateau, which is screened by the Hamgyeongsanmaek and Nangnimsanmaek Ranges, effectively blocking outside moisture, and the eastern coastal region of Hamgyeongbuk-do province, which receives the coastal cold current. Of particular note is Cheongjin in Hamgyeongbuk-do province, which receives a mere 615mm of rainfall per year.
The following locales have annual average precipitation rates exceeding 1500mm: Geoje (2007.3mm), Seongsan (1966.8mm), Seogwipo (1923.0mm), Changwon (1545.4mm), Busan (1519.1mm), and Jinju (1512.8mm) (Figure 1-7). Areas with annual precipitation above 1300mm include: Jeju City (1497.6mm), Gangneung (1464.5mm), Daejeon (1458.7mm), Tongyeong (1450.8mm), Seoul (1450.5mm), Yeosu (1439.0mm), Sokcho (1402.2mm), Gwangju (1391.0mm), Jecheon (1387.8mm), Namwon (1380.4mm), Chuncheon (1347.3mm), Wonju (1343.6mm), Taebaek (1324.3mm), Jeongeup (1317.3mm), Jeonju (1313.1mm), and Suwon (1312.3mm).
Average annual precipitation rates and their distribution are closely linked to terrain and atmospheric pressure patterns. The reason for the high annual precipitation rates along the southern coastal region and the mountain region around Mt. Jiri is not just due to topography, but the north-south shifting rainy season front also makes a prolonged stay in the region, and added to this is the fact that these areas also feel the effect of seasonal monsoons.
Areas that receive on average over 1100mm of annual precipitation include Yeongju (1290.9mm), Seosan (1285.7mm), Ulsan (1277.1mm), Mungyeong (1259.8mm), Boryeong (1244.3mm), Cheongju (1239.1mm), Incheon (1234.4mm), Miryang (1229.4mm), Cheonan (1226.5mm), Chungju (1212.7mm), Gunsan (1202.0mm), Mokpo (1163.6mm), Pohang (1152mm), and Uljin (1119mm).
Those regions of the peninsula that receive less than 1100mm of average annual precipitation are generally limited to the Yeongnam region in the southwest and include Yeongdeok (1072.7mm), Gumi (1072.5mm), Andong (1066.4mm), Daegu (1064.4mm), Yeongcheon (1046.8mm), and Uiseong (1031.7mm). Annual rainfall is particularly slight in the interior regions of Yeongnam, which essentially forms a gigantic basin encircled to its west and north by the Sobaeksanmaek Range, to its east by Taebaeksanmaek Range, and with high peaks also to its south.
(2) Summer Precipitation Rates
With the exception of some insular regions, during the Korean Peninsula’s rainy season between June and September almost all areas receive over 60 percent of their annual precipitation (Table 1-3). And among these months it is July, during the peninsula’s rainy season, that records the highest rainfall. However, the rates of annual precipitation can vary by year depending on the influence of the rainy season and monsoons.
| City | June precipitation | July precipitation | August precipitation | September precipitation | Total rainy season precipitation | Average annual precipitation | Precipitation outside the rainy season |
|---|---|---|---|---|---|---|---|
| Seoul | 133.2 | 394.7 | 364.2 | 169.3 | 1,061.40 | 1,450.50 | 0.732 |
| Incheon | 112 | 319.6 | 285.8 | 153.5 | 870.9 | 1,234.40 | 0.706 |
| Daejeon | 206.3 | 333.9 | 329.5 | 169.7 | 1039.4 | 1,458.70 | 0.713 |
| Gwangju | 181.5 | 308.9 | 297.8 | 150.5 | 938.7 | 1,391.00 | 0.675 |
| Daegu | 142.6 | 224 | 235.9 | 143.5 | 746 | 1,064.40 | 0.701 |
| Ulsan | 176.8 | 232.3 | 240.3 | 168.2 | 817.6 | 1,277.10 | 0.64 |
| Busan | 206.7 | 316.9 | 255.1 | 158 | 936.7 | 1,519.10 | 0.617 |
The rainy season begins with the expansion of the North Pacific high-pressure system and the northward movement of the rainy season front. Generally, the rainy season begins on the Korean Peninsula in late June and continues into late July. The rainy season front, forming between the North Pacific high-pressure and polar high-pressure systems, is also known as the polar front. The rainy season front stretches for some 300 kilometers in width, and meanwhile the approach of the lower pressure system that develops in the Yangtze River region in China also brings with it heavy rainfall. The rainy season front reaches the peninsula’s southern coast in late June, makes its way to the central regions by mid-July, and by late July reaches as far as the Yalu River region on the Chinese border.
As the rainy season front moves northward towards Manchuria the hot and humid North Pacific air mass begins to dominate the Korean Peninsula and the sweltering high summer season begins in earnest. During this time, although there are cases of localized thunderstorms, there is not much rainfall. The rainy season front that moved northward will shift again south resulting in the briefer autumn rainy season in September.
During the high summer months between the summer and autumn rainy seasons the Korean Peninsula often experiences rain-packed monsoons. Generally, the months between July and September see the approach of monsoons, with very powerful storms striking the southern regions on average every other year, and the central regions once every four years. While the economic damage caused by monsoons has increased exponentially with urbanization and industrialization, the effective dissemination of meteorological information has gradually reduced the human causalities of such storms.
(3) Winter Precipitation Rates
The average winter precipitation of the Korean Peninsula accounts for only 10 percent of its total annual precipitation. The northwest seasonal monsoon that blows from out the Siberia high-pressure system is cold and dry. However, after picking up moisture as it passes over the Yellow Sea, these winds can result in heavy snowfalls once they encounter mountainous regions. The alpine coastal regions of Korea’s west coast from Jeollabuk-do into Jeollanam-do provinces and including such cities as Jeongju, Jeongeup, Gochang, and Yeonggwang, can experience heavy snowfalls brought in by the northwest monsoons, often resulting in transportation disruptions.
The heavy snowfalls that often hit the Yeongdong region (corresponding to coastal Gangwon-do provinces in both North and South Korea) in February are usually the result of north-easterlies that blow down from a migratory anticyclone pattern as it passes over the northern part of the peninsula after having separated from the Siberian high pressure system. The heavy snowfalls in the mountainous regions are usually the result of moisture-laden winds blowing in from the sea.
The area of Korea with the heaviest recorded snowfall is the island of Ulleung-do, which on January 31, 1962 recorded snowfall at a depth of 293.6 cm. In heavy snowfall prone Ulleung-do one can observe the so-called “udegi,” a unique form of house that developed to cope with snowfall, and even today during periods of heavy snowfall residents will don snowshoes called “seolpi.”
(4) Variations in Annual Precipitation
The Korean Peninsula belongs to the humid climatic zone. However, some years can witness serious variability in its average precipitation resulting in frequent flooding and drought. Though years of extreme annual precipitation or dryness will vary by region, generally speaking a region will experience extreme precipitation over three times more often than extreme dryness. To take Seoul as an example, it received 633.7mm of precipitation in 1949, while in 1990 it received 2355.5mm, over 3.7 times more. Over the last decade, the highest annual precipitation for Seoul was 2044mm and the lowest 1212mm (Table 1-4).
| Year | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 |
|---|---|---|---|---|---|---|---|---|---|---|
| Annual precipitaion rate | 1,386 | 1,388 | 2,012 | 1,499 | 1,358 | 1,682 | 1,212 | 1,356 | 1,564 | 2,044 |
Because the Korean Peninsula receives the bulk of its rainfall in the summer months, whether the annual precipitation rate shows a great deal of variability between years will largely depend on whether a given summer received a lot of little rain. To take some examples, in terms of peninsula-wide rainfall, the years 1939, 1942, 1944, 1988, and 1994 were years of low precipitation, while 1925, 1941, 1948, 1963, 1998, and 2003 were years of high precipitation. These were respectively years of droughts and severe flooding.
Most weather-related disasters in Korea are the result of severe flooding brought about by monsoons or periods of heavy rainfall. The years 1998, 1999, 2002, 2003, and 2006 can be pointed out as years in which South Korea experienced over one trillion won (US$1 billion) in precipitation-related damages. The year 2002 was particularly bad. On August 31 of that year Typhoon Rusa dumped 870.5mm of rain in a single day on the Gangneung region on South Korea’s east coast, with the heaviest hour recording 100.5mm of rainfall. In the Gangneung area alone there were 68 storm-related causalities, including 46 deaths, 5 missing, and 17 injured, and over 800 billion won ($US800 million) in property damage.
