The Seoul Metropolitan Government is constructing a massive underground flood-control tunnel to protect residents from increasingly frequent extreme rainfall events [1].
The project addresses a critical infrastructure gap as climate change increases the frequency of "climate-crisis-type" heavy rains. Existing sewer pipes in the city are designed to handle 95 mm of rain per hour [1], but recent extreme events have reached 100 mm per hour, overwhelming the system and causing urban flooding [1].
To mitigate this risk, the city is building a giant tunnel at a depth of 40–50 meters underground [1]. This deep-level infrastructure is designed to capture and divert excess water that the surface sewers cannot process during peak intensity.
Data shows a sharp increase in the frequency of these weather events. In the decade between 2000 and 2009, Seoul experienced two extreme-rainfall events [1]. This number rose to three during the 2010s [1]. In the current decade, the city has already seen six such occurrences [1]. The first recorded extreme-rainfall event in Seoul took place in 2001 [1].
Ban Ki-sung, a disaster specialist for YTN, said that extreme rainfall of more than 100 mm per hour, which used to occur once every few decades, is now happening almost every year. He said that as warming increases the amount of saturated water vapor in the atmosphere, "water bombs" that pour down on specific areas for short periods are becoming commonplace [1].
The tunnel aims to provide a buffer against these unpredictable surges, ensuring that water is moved away from residential areas before it can accumulate on the streets.
“Existing sewer pipes in the city are designed to handle 95 mm of rain per hour.”
Seoul's shift toward deep-tunnel infrastructure signals a transition from traditional drainage management to 'climate-adaptation' engineering. By moving the primary flood-defense system 40–50 meters below the surface, the city is acknowledging that surface-level upgrades are no longer sufficient to keep pace with the accelerating volatility of East Asian monsoon patterns and global warming.
