Analysis of causes of
localized heavy rains
in Korean and countermeasures
Heavy Rain
Rain with strong time and spatial concentration
HEAVY RAIN have no clear definition, but it is generally called heavy rain when the daily precipitation is 10% of the annual precipitation, or when it rains more than 30mm an hour.
In case of Korea...
Heavy rain is common when southwest air currents, including a lot of water vapor, enter the rainy season(Jangma) front or when typhoons pass, and it falls a lot in valleys and mountainous areas due to the influence of topography.
Usually, in summer, torrential rain with more than 100mm of daily precipitation frequently falls, and in the southern part of the country where typhoons blow, daily precipitation may exceed 500mm locally.
Characteristics of Heavy Rain
Heavy rain occurs mainly in cumulonimbus clouds formed by strong updraft currents. There are several factors: the instability of rainy season(Jangma) fronts, typhoons, low and high pressure edges.
During the heavy rain, the size of the cumulonimbus clouds usually reaches several~tens of kilometers in the horizontal direction, and tropopause (10 to 15 kilometers at altitude), the top of the troposphere in the vertical direction.
The developed cumulonimbus clouds be seen as a 'huge sky reservoir' containing about 10 to 15 million tons of water, and these clouds spray rain as they pass by, usually called 'thundery (Sonakseong) precipitation.' If this cloud is stagnant in one place and if it continues to rain, it becomes heavy rain.
The life time of the heavy rain is only about 1 to 2 hours, but when the surrounding weather conditions are satisified, the process of creating and disappearing rain cumulonimbu clouds is repeated many times, which occurs heavy rain continues for several days.
• As for the temporal characteristics, instability caused by solar radiation accelerates during the day and is latent, and then activity is strong at night. Looking at the spatial factors of heavy rain, there are also local characteristics in which convective instability is strongly developed due to topographical effects such as coastal, mountain, and inland.
• As for the spatial characteristics (the topographical characteristics of Korea), it is very difficult to predict accurately because Korea is surrounded by the sea on three sides and has a great topographical effect due to high mountains or valleys are often concentrated in narrow areas of tens of in a short time of two to three hours.