Three Things to Know: Historic Flooding in Seoul, South Korea

1. Record-setting rainfall recorded in Seoul, South Korea
   • Torrential rains hit the South Korean capital of Seoul. A month’s worth of rain fell in southern Seoul from Monday into Wednesday.
   • More than 100 mm (~3.9 inches) of rain per hour fell south of the capital late Monday. According to the Korea Meteorological Administration (KMA), parts of the city experienced 141.5 mm of rain (5.5 inches) per hour.  By Wednesday morning (local time), 525mm (~20.7 inches) of rain was observed in Seoul and 532.5 mm (~21.0 inches) recorded in the neighboring county of Yangpyeong. Rainfall is expected to subside throughout Wednesday. ^[1]  

2. Several fatalities reported, thousands of homes and other buildings damaged
• The intense precipitation over South Korea generated both flash and riverine flooding. In Seoul, urban drainage systems were unable to “keep up” with precipitation and the high degree of paved surfaces prevented flood waters from infiltrating into the ground surface. The Han River, which borders the southern edge of Seoul, swelled with flood waters, overflowing banks and engulfing sections of the city. Portions of bridges spanning the Han River were partially submerged.
• As of Wednesday, nine people have been killed by the flooding in South Korea, and over 2,800 homes and buildings were damaged.¹ Basement apartments, known as banjiha, are particularly susceptible to flooding as they are typically situated below ground elevation. Many of the fatalities reported were in these types of homes. The full extent of damage is yet to be determined, as is common with major flooding events.
• In addition to flooded homes and business, several major roadways were closed, and subway stations blocked by flood waters. As of Wednesday morning, emergency and restoration crews have opened most highways and subway lines.
• Warnings of mud and landslides were issued to the surrounding cities and towns outside of Seoul.

3. Uncharacteristically heavy precipitation rates for typical monsoon season
   • Monsoon season extends from June to September for most of Asia, including the Korean Peninsula. Heavy rainfall and flooding are the most common and destructive perils in this region. Typically, about 24 inches of rain is expected during monsoon season, triggering inland flooding and landslides. The climatological August mean daily rainfall (1981 – 2010) rates in South Korea typically range from 6-10 mm/day.^[2] (Figure 1). The observed rainfall rates in Seoul and surrounding cities this week surpassed the climatological averages by a significant margin.

Figure 1

• The impact of climate change is felt in Korea in terms of precipitation, as warmer air can hold more moisture. Average temperatures in the Korean Peninsula have increased substantially from 1912 to 2008 (+1.7°C), which has in turn led to an increase in rainfall (+19%).²
• Despite mitigation efforts by the Republic of Korea such as land use planning and structural safety, flooding continues to be a major hazard. The population of Korea has grown substantially with more and more people moving to urban centers such as Seoul, increasing the likelihood of fatalities and loss during a flood event.

CoreLogic is continuing to monitor the situation in Korea. All updates will be posted to HazardHQ.com.

^[1] Roh, Joori, Torrential rain lessesn in S. Korea capital amid heavy flood damage. (Reuters 2022). https://www.reuters.com/world/asia-pacific/torrential-rain-lessens-skorean-capital-amid-heavy-flood-damage-2022-08-10/?taid=62f381b71a1c2c0001b5f821&utm_campaign=trueanthem&utm_medium=trueanthem&utm_source=twitter. Accessed August 10 2022.

^[2] World Meteorlogical Organization, Reducing Disaster Risk in Cities – the Republic of Korea. (WMO 2011). https://public.wmo.int/en/bulletin/reducing-disaster-risk-cities-%E2%80%94-republic-korea%E2%80%99s-experience. Accessed August 10 2022.