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SNU expert expects 'unthinkable' monsoon season

Published: 07 May. 2025, 19:03

Firefighters carry stranded residents as a part of efforts to evacuate 36 villagers in Yongchon-dong in Seo District, Daejeon, after overnight rain flooded the area on July 10, 2024. Fire authorities mobilized 13 pieces of equipment and 73 personnel to rescue residents. [NEWS1]

“Even if the unthinkable happens, I will not be surprised.”

The ominous comment was made by Son Seok-woo, professor and head of the Monsoon Special Weather Research Center at Seoul National University's School of Earth and Environmental Sciences on Wednesday when asked about predictions for this year’s rainy season.

“Last summer, we frequently saw downpours exceeding 100 millimeters [4 inches] per hour followed by unprecedented heat waves and tropical nights — none of which we had anticipated,” said Son.

As Son pointed out, forecasting monsoon weather patterns is becoming increasingly difficult. With the rainy season set to begin next month, experts are urging pre-emptive measures to mitigate potential damage from torrential rain.

According to a three-month outlook released by the Korea Meteorological Administration (KMA), there is a 40 percent chance that rainfall in June, when the monsoon typically begins, will be either above or near average. The probability of below-average precipitation stands at 20 percent.

“Strengthening anticyclonic circulation around the Korean Peninsula may lead to the inflow of hot and humid southwesterly winds, resulting in higher temperatures and increased rainfall,” said the KMA.

For July, the outlook remains similar, with above or near-average rainfall expected, particularly in central regions including Seoul.

Firefighters take safety measures on a flooded road in North Chungcheong on Sept. 21, 2024. A taxi is also flooded by the rainwater. [NATIONAL FIRE AGENCY]

Torrential rain goes tenfold

More concerning than the amount of rain is its intensity. The frequency of short-duration, high-intensity summer downpours has been rising markedly across East Asia. In particular, Korea, western Japan and inland China have seen a sharp increase in such events.

Between 1961 and 2020, the number of days with rainfall exceeding 100 millimeters in Korea increased nearly tenfold. Last year alone, “extreme rainfall” events — with more than 100 millimeters falling per hour — were recorded 16 times nationwide.

The nature of the monsoon is also changing. In the past, heavy rainfall was typically concentrated in July during the monsoon and again in mid-August during what was known as the “autumn monsoon.”

Recently, however, rainfall has become more continuous throughout the summer, with dry periods in the rainy season disappearing. This means that torrential rain can now strike at any time.

In addition to the traditional monsoonal stationary front, summer rainfall is now driven by a complex mix of pressure systems, further complicating forecasts.

“Clouds can develop rapidly over areas like Gyeonggi Bay, bringing downpour to the greater Seoul metropolitan area in just one or two hours, which are extremely difficult to predict,” Son said. “Localized convective rainfall, where heavy rain falls only in specific areas, is also becoming more frequent.”

Firefighters rescue individuals who were trapped in a building following a nearby road flooding in Paju, Gyeonggi, on July 18, 2024. [NEWS1]

Compounding heat waves and heavy rain

Weather experts are warning of an increased likelihood of “compound disasters” this summer, where extreme heat and torrential rain occur simultaneously.

In particular, North Gyeongsang, which suffered unprecedented wildfires earlier this year, is at high risk of secondary disasters such as landslides during the monsoon.

A joint government investigation found that 201 sites in the region require urgent restoration to prevent landslides. Safety inspections are also recommended in major urban areas like Seoul, where sinkholes and ground subsidence incidents have occurred in recent months.

“Compound disasters are becoming highly prominent in East Asia, but unfortunately, we still don’t know exactly why,” Son said. He stressed the importance of continued monitoring.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY CHON KWON-PIL [[email protected]]