Record autumn downpour floods Seoul as El Niño raises rainfall concerns

Unusually heavy autumn rain battered Seoul and other parts of the country on Sunday, causing flooding in some areas, with a strengthening El Niño expected to bring more rain later this fall.

Seoul received 51.4 millimeters (2 inches) of rain on Sunday, with 35.1 millimeters (1.4 inches) falling in just one hour during the afternoon, according to the Korea Meteorological Administration (KMA). The downpour set a new record for hourly rainfall in Seoul since weather observations began in 1907.

Strong winds also brought down leaves, which accumulated and clogged storm drains. Because rainwater could not drain properly, roads in several areas were flooded.

"Conditions were favorable for the strong development of rain clouds as relatively large amounts of moisture flowed in from the south while cold, dry air moved down from the northwest," said Lee Gwang-yeon, a forecast analyst at the KMA. "Because this is the season when leaves fall, flooding can occur even with less rainfall than during the summer."

Rain is expected to fall mainly in southern regions and on Jeju on Tuesday, with showers also forecast for Seoul and other parts of the country on Wednesday. Jeonnam-Gwangju and the Gyeongsang provinces could receive up to 60 millimeters of rain through Wednesday.

The risk of heavy autumn rainfall could increase further in the coming months.

The KMA has forecast above-average rainfall in November and December due to an unusually strong El Niño developing in the tropical Pacific Ocean.

El Niño is a climate phenomenon characterized by warmer-than-average sea surface temperatures in the equatorial Pacific Ocean. The current event is expected to become one of the strongest "super El Niño" events since 1950.

"El Niño will continue to intensify ahead of its forecast peak in December," the World Meteorological Organization said in a press release on Oct. 8. "It is likely to bring above-average temperatures to much of the globe and shift rainfall patterns, increasing the risk of drought and floods in different regions."

The effects of El Niño vary by region. In Korea, it can worsen drought conditions in early autumn by reducing rainfall but is likely to bring above-average precipitation in late autumn. As El Niño develops, northerly winds tend to weaken while more moisture flows in from the south.

During previous super El Niño events, November rainfall was two to three times the seasonal average.

Experts warned that the risk of clogged storm drains is particularly high as the autumn foliage season ends and leaves begin to fall.

"Simulations of heavy rainfall showed that when debris reduced the drainage area to one-fifth of its original size, water infiltration effectiveness fell to 30 percent and the effectiveness of reducing water depth dropped to about half," Kim Jong-min, a researcher at the Korea Institute of Civil Engineering and Building Technology, said. "To prevent flooding, it is important to keep storm drains clear of debris."

BY CHON KWON-PIL [[email protected]]