Korea, South

THE REPUBLIC OF Korea is located in the southern part of the Korean peninsula and associated islands that lie between 33 and 43 degrees N and extend southward into the northeastern Asian continent. Its peninsular configuration as an appendage of the Asian continent and mid-latitudinal location lead the continental influence on the East Asian monsoon climate of South Korea. South Korea has four distinct seasons. In summer, a hot, moist climate dominates South Korea, which is located in the western flank of the North Pacific high pressure system, while cold, dry northwesterly winds from the Siberian high pressure system take over the winter climate. In the transition periods of spring and fall, clear, pleasant weather occurs more frequently and the land-sea breeze becomes dominant with weakened monsoon wind.

The average annual temperature and the annual temperature range are 54 degrees F (12.3 degrees C) and 78.6 degrees F (25.9 degrees C), respectively. The lowest annual average temperature is found in the northeastern interior mountainous regions, while the highest occurs in Cheju Island, located in the South Sea. The temperature range is also much greater in the northeastern interior mountainous regions than in the south and along the coasts. These temperature patterns show influence of latitude, altitude, and the continent on temperature distribution. Summer is hot, with very little regional difference in temperature, while winter is very cold, but has great regional variation in temperature. The mean temperature of warmest month and coldest month is 76.8 degrees F (24.9 degrees C) and 30 degrees F (minus 1 degree C), respectively.

South Korea is a region of abundant precipitation, with an annual average precipitation of 51.5 in. (1,310 mm.). A noticeable seasonal variation in precipitation is, however, found because of the monsoon climate. In summer, heavy rainfalls are accompaniedby a Changma front, a quasi-stationary front extending from Japan through Korea into southeastern China, and tropical cyclones are substantial and represent approximately 70 percent of annual precipitation. Heavy regional showers, often exceeding 12 in. (300 mm.) of rainfall in a day, or sometimes more than 32.5 in. (800 mm.), also characterize summer rainfall. As in much of Asia, winter in Korea is dry. Less than 10 percent of annual precipitation occurs in winter. Heavy snowfall is found on islands and in the eastern coastal regions. The spatial distribution of annual mean precipitation generally increases southward, but its spatial pattern is complicated because of complexity of topography.

Over the last century, a gradual increase (2.8 degrees F, or 1.6 degrees C, over 100 years) in mean temperature has continued, but a warming trend has become even more significant since the 1980s. The mean winter temperature has drastically increased, while no distinct increase in mean summer temperature is found. Both diurnal and annual temperature ranges, however, have been significantly reduced due to the noticeable increase in minimum temperatures. Since the late 20th century, considerable decrease in the frequency of frost days in spring and autumn has extended growing season length. The frequency and duration of heat waves and warm nights have notably increased. Although a gradual increase of annual precipitation is found, there is some controversy about the temporal trend of annual precipitation because of its considerable variation. Along with a gradual increase in annual precipitation, a significant decrease of annual rain days results in the increased rainfall intensity once rain occurs. The frequency of severe drought has also increased, especially in the southern part of South Korea.

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