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40 degrees, 20 inches of rain: Extreme weather is Korea's new normal

Published: 21 Jul. 2025, 13:36 Updated: 21 Jul. 2025, 19:40

A resident looks at homes and other buildings damaged from mud and debris that swept through Oejeong Village in Sancheong County, South Gyeongsang, following heavy rain and a landslide on July 20. [NEWS1]

Korea is facing a summer of weather extremes, with unusually early heat waves and shifting bouts of torrential rain, raising concerns that these once-rare phenomena are fast becoming the new normal under accelerating climate change.

Record-breaking heat wave

The first signs emerged in early July with a wave of extreme heat that scorched parts of the country. On July 8, automatic weather stations recorded temperatures exceeding 40 degrees Celsius (104 degrees Fahrenheit) in parts of Gyeonggi, including Gwangmyeong and Paju. In Seoul, the daytime high reached 37.8 degrees Celsius, the highest for early July since record-keeping began in 1907.

The cause was a “heat dome” effect, created when the North Pacific and Tibetan high-pressure systems converged to trap hot air above the peninsula. The resulting stagnation prevented the buildup of heat from dissipating, driving temperatures to historic levels.

Strawberry greenhouses in Sinan-myeon, Sancheong County, South Gyeongsang, on July 21 are severely damaged by recent heavy rains. [YONHAP]

'Once-in-200-year downpour'

The oppressive heat gave way to a sudden onslaught of heavy rain starting last Wednesday. More than 500 millimeters (20 inches) of rain fell in parts of South Chungcheong, South Jeolla and South Gyeongsang over several days. On Thursday alone, Seosan in South Chunghceong recorded 413.4 millimeters and Gwangju 426.4 millimeters, both exceptional one-day totals. In Pocheon, Gyeonggi, 104 millimeters of rain fell in just one hour on Sunday, a deluge that meteorologists estimate occurs once every 200 years.

The Korea Meteorological Administration (KMA) attributed the unusual rainfall to the prolonged clash between cold, dry air descending from the north and hot, humid air arriving from the south. This standoff created ideal conditions for heavy rain clouds to persist over affected regions.

Despite the end of the summer monsoon in parts of southern Korea, heavy rains continued, moving across the country and defying seasonal norms. The North Pacific high-pressure system remained anchored to the east, preventing low-pressure systems from exiting the region and causing them to linger over Korea

“The cold, dry air from the north and the hot, moist air from the south remained locked in place for an extended time, leading to unusually heavy rainfall,” said Lee Chang-jae, a KMA forecast analyst.

An older person rests in the shade beneath a bridge near Jidong Bridge in Paldal District, Suwon, Gyeonggi, to escape the heat on July 11. [NEWS1]

Growing extremes

Experts warn that such abrupt and extreme weather patterns are likely to become more frequent as global temperatures rise. There are concerns that, as seen in Sancheong, South Gyeongsang — which received nearly half its annual rainfall in a single event — heavy rain damage may become increasingly concentrated in specific areas.

“Before the 2022 Seoul floods, rain at rates over 100 millimeters per hour was rare. Now, such events are becoming more common,” said Son Seok-woo, professor at Seoul National University’s School of Earth and Environmental Sciences.

“For every one-degree rise in temperature, the atmosphere can hold about seven percent more water vapor. This intensifies vertical atmospheric movement and increases the likelihood of extreme rainfall.”

Kim Hae-dong, a professor of environmental engineering at Keimyung University, noted that rising ocean temperatures linked to climate change are a key driver of recent heavy rainfall in the southern Chungcheong region.

“In the future, summer rainfall will likely concentrate along narrow, elongated rain bands that bring intense localized downpours,” he said.

Kim added that weather forecasting must become bolder and cities should expand underground water storage to cope with flash floods.

A citizen shields himself from the sun beneath a large parasol at a crosswalk in front of Pohang City Hall in North Gyeongsang on July 21. [NEWS1]

More heat

After the rains, sweltering conditions are expected to return.

According to the KMA, as rain clouds retreat and the monsoon ends in the central region, most of the country will face “steam bath” conditions with apparent temperatures near 33 degrees Celsius. Tropical nights, where the overnight low remains above 25 degrees, are also forecast in some areas. Through Tuesday, up to 60 millimeters of heavy showers are expected across the interior.

Son warned that this summer’s heat may rival or exceed 2018, when Seoul recorded its most intense heat wave.

“This year’s heat started earlier. There is a high chance it will persist longer and may even exceed 40 degrees Celsius,” Son said.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY JUNG JONG-HOON [[email protected]]