Monster rainstorm batters Geoje with once-in-200-year deluge 

A monster rainstorm of an intensity seen only once every 200 years battered Geoje, South Gyeongsang, on Monday.

The deluge — overwhelming in both intensity and volume and comparable to a typhoon — triggered a series of landslides and flooding across the province.

Geoje had received 633.2 millimeters (24.9 inches) of rain as of 4 p.m. Monday, according to the Korea Meteorological Administration (KMA). The figure represents the highest daily rainfall since weather observations began there in 1972.

Cumulative rainfall since Saturday reached 906.9 millimeters. That three-day total is nearly equivalent to the 935.1 millimeters of rain the region typically receives over an entire summer based on the yearly average measured between 1991 and 2020.

Only two locations in Korea have recorded more rain in a single day: In August 2002, Gangneung received 870.5 millimeters of rainfall and Daegwallyeong received 712.5 millimeters when Typhoon Rusa swept through Gangwon.

Earlier Monday, 124.5 millimeters of rain fell in Geoje in a single hour. It surpassed the previous hourly record of 96.5 millimeters set on July 5, 2001.

It was also the fourth-highest hourly rainfall ever recorded at any of the country’s Automated Synoptic Observing System stations, including stations that have since closed. The KMA said such rainfall would statistically be expected only once every 200 years.

Nearby Tongyeong also experienced an extreme downpour, with 97.4 millimeters falling in an hour, an intensity likewise associated with a once-in-a-century event. The deluge set a new hourly rainfall record for the city, while its daily total of 450 millimeters was also the highest since observations began.

The extreme rainfall was concentrated along the southern coast of South Gyeongsang because a southerly low-level jet carrying hot, moisture-laden air across the sea collided with the coastal terrain, which helped rain clouds intensify rapidly.

In particular, a narrow corridor of moisture formed between a low-pressure system that had evolved from Typhoon Dolphin, the 13th typhoon of the season, and a high-pressure system to the northeast. Strong southerly winds funneled moisture through the corridor, pushing rainfall to record levels.

“As the low-pressure system moved through, the high-pressure system ahead of it blocked its path, and the resulting weather pattern continued to draw large amounts of moisture into the region,” KMA forecaster Gong Sang-min said. “The moisture-laden air continued to collide with the terrain, and heavy rain persisted.”

In recent years, sudden bouts of extreme rainfall have become more common even after the monsoon season has ended. Last year alone, Korea recorded 15 instances of rainfall exceeding 100 millimeters per hour, 11 of which occurred after the monsoon season.

“As the traditional monsoon pattern breaks down, summer rainfall is shifting from prolonged rain over broad areas to enormous amounts of precipitation falling all at once over highly localized areas,” Yeh Sang-wook, a professor in the Department of Marine Convergence Engineering at Hanyang University, said. “We have reached a point where extreme rainfall at any time during the summer would no longer be unusual.”

Abrupt swings in weather extremes, including record-breaking downpours following severe heat waves and drought, are also compounding the damage. Torrential rain falling on drought-weakened ground has washed away soil and triggered a series of landslides.

Last week, the National Fire Agency issued a nationwide fire-service mobilization order to provide emergency water supplies to drought-stricken areas of South Gyeongsang. Just days later, torrential rain forced the agency to issue another national mobilization order.

Climate change is increasing the risk of a “double punch” from extreme heat and torrential rain, experts say.

“Extreme weather events in which severe heat and torrential rain alternate within a short period will become more frequent because of climate change,” Kim Seung-bae, a senior official of the Korea Natural Disaster Association and a former KMA spokesperson, said. “We need to move beyond patterns based on the past and establish a system capable of responding to a combination of weather-related disasters.”

BY CHON KWON-PIL [lee.soojung1@joongang.co.kr]