Gangneung has recently experienced a severe drought. As of September 12, the water level of the Obong Reservoir in Gangneung dropped to 11.6%, an extremely low value compared to the climatological average. In contrast, Gunsan suffered intense heavy rainfall and severe flooding this year. These two regions illustrate a clear meteorological east–west contrast phenomenon, where drought and flooding coexist simultaneously in Korea.
This contrast is strongly influenced by differences in orographic lifting and downslope flows caused by the Taebaek Mountains, variations in airmass inflow pathways, and the distinct oceanic characteristics of the Yellow Sea and the East Sea.
As a result, the two regions experience sharply contrasting climate conditions.
This phenomenon is closely linked to the broader characteristics of Korea’s climate.
Against this background, there is a growing need to analyze the interaction between localized heavy rainfall and Korea’s climate, using Gangneung and Gunsan as representative regions on the eastern and western sides of Korea.
Such analysis provides valuable scientific foundations for understanding atmospheric contrast structures and for improving Korea’s resilience in an era of climate crises.
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Why is localized torrential rainfall closely connected to the climatic characteristics of Korea?
Korea Meteorological Administration (KMA) makes a 'Heavy Rain Advisory' when the accumulated rainfall reaches 60 mm or more in 3 hours, or 110 mm or more in 12 hours. A Heavy Rain Warning is issued when the respective thresholds reach 90 mm and 180 mm. Concentrated heavy rain events in Korea mainly occur between June and September, and when more than 30 mm of rainfall per hour falls over a small area,
it is classified as a localized torrential downpour.
A combination of climatic, topographic, and atmospheric dynamic factors
During summer, Korea is influenced by the East Asian monsoon, which brings large amounts of moisture northward through southwesterly winds. When this hot and humid air rises along the Changma (meiyu–baiu) front or low-pressure convergence zones, strong convective clouds develop, producing intense rainfall in a short period of time. In addition, Korea’s complex mountainous terrain forces incoming air to ascend, enhancing orographic precipitation and causing certain areas to receive concentrated rainfall even from the same convective cell.
Mesoscale Convective Systems
Mesoscale Convective Systems (MCSs) also frequently form over Korea in summer. These systems can remain over a given region for several hours and produce hundreds of millimeters of rainfall, making them a major driver of localized torrential downpours. Recently, climate change has increased atmospheric temperatures and moisture-holding capacity. According to the Clausius–Clapeyron relationship, this leads to higher rainfall intensity per unit time, increasing the frequency of extreme precipitation events in which larger amounts of rain fall over shorter periods.
The effect of Ulbanization
Urbanization has also expanded impermeable surfaces, accelerating runoff and worsening flooding in cities even when the same amount of rain falls. Furthermore, interactions between the ocean and atmosphere around the Korean Peninsula—such as moisture transport by southwesterly “atmospheric rivers”—play an important role in triggering heavy rainfall in specific regions. When moisture supplied from the ocean is continuously and intensively transported into Korea, it interacts with monsoonal flow, low-pressure systems, and stationary fronts to produce extremely high hourly rainfall rates. All of these combined factors are closely associated with Korea’s climatic characteristics, including the summer monsoon, maritime influences, and complex terrain.
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30-year Trends in Heavy Rainfall in the Korea
Over the past several decades (roughly the last 30 years), total precipitation over the Korean Peninsula has shown regional and seasonal variation, but the frequency and intensity of extreme precipitation events (short-duration heavy rainfall) have exhibited an increasing trend. In particular, analyses report that extreme rainfall events during the summer (June–August) and the monsoon season have become more frequent and
more intense.
About the Heavy rain in Seoul
Between 2010 and 2019, the frequency of hourly rainfall exceeding 50 mm increased by approximately 1.5 times compared with cases observed from 1973 to 2009. In some regions, the frequency increased by more than 6.4 times. This trend continues into recent years. During the record-breaking long monsoon season of summer 2020, there were 15 occurrences of 12-hour rainfall exceeding 110 mm. In August 2022, Seoul recorded an hourly rainfall of 141 mm.
Regional analyses based on observational data also show statistically significant upward trends in extreme rainfall indicators—such as maximum 1-hour, 3-hour, and daily precipitation, and the number of very heavy rainfall days—when assessed over the past 30 years (1993–2022) and 50 years (1973–2022). Although the magnitude varies by region and season, the general direction indicates an increase in short-duration heavy rainfall. Case studies, including the consecutive and intense rainstorms of 2020, highlight the growing possibility of rainfall clustering (serial occurrence of heavy rain events). Regional case analyses also illustrate linkages among rainfall persistence, rainfall intensity, and atmospheric transport or stagnation patterns.
Climate model projections similarly indicate that the intensity and frequency of extreme rainfall will continue to increase depending on the level of global warming. The IPCC AR6 assesses an increased likelihood of extreme rainfall in East Asia and the Korean Peninsula with medium to high confidence, warning of heightened regional rainfall and flood risks.
The unique topography of the Korean Peninsula—mountain ranges along the central axis and its narrow, peninsular shape—combined with rapid urbanization, exacerbates the impacts of observed heavy rainfall (e.g., flooding and inundation). In other words, even with the same amount of rainfall, orographic uplift and increased impervious surface area create structural vulnerabilities that amplify damage intensity.