"One-Third of Annual Rainfall Poured Down"... Cause of 'Autumn Torrential Rain' Unveiled

In mid-September 2024, long after the monsoon season ended.

A massive amount of rain poured over the southern coast in the span of two days, recording 529 mm in Changwon, 403 mm in Busan, and 381 mm in Geoje.

Changwon received one-third of its annual rainfall in just two days, with hourly precipitation peaking at 104.9 mm.

The cause of the heavy rain was a stationary front, where air masses with different properties met and clashed intensely.

According to a joint study by researchers from KAIST and the APEC Climate Center, frontal precipitation bands affecting South Korea, such as stationary fronts, have moved further northward toward the country compared to the past.

The research team analyzed 47 years of data from 1979 to 2025, revealing that the location of the fronts over the past 20 years has shifted up to 213 km northward compared to the earlier 20-year period from 1979 to 1998.

The northward shift of the fronts was particularly prominent in the Yangtze River basin of China and southern Japan from late June to mid-July, the peak of the monsoon season, while on the Korean Peninsula, the fronts moved more than 200 km northward in September, the late summer.

[Kim Hyung-jun, Professor at KAIST Department of AI and Future Technology: Rain that was originally supposed to fall over the ocean might fall over land, and in particular, such phenomena tend to occur quite strongly in late summer, which can also be called late September or early autumn.] The researchers pointed to persistently high sea surface temperatures caused by climate change and the weakening of upper-level jet streams, which would otherwise block the northward movement, as the causes.

Frontal precipitation affecting South Korea has also been analyzed to have increased in intensity.

According to a domestic research team, the intensity of frontal heavy rain in East Asia increased by 17% between 1958 and 2015.

This means that because the fronts have moved further north than in the past, intense torrential downpours can occur on the Korean Peninsula at any time, even after the monsoon season has passed.

The researchers also analyzed that as hot and humid air from the south pushed upward, heatwaves occurred on the southern side of the front where it did not rain.

Reported by Seo Donggyun | Video by Kim Jong-tae | Graphics by Kim Ye-ji | Produced by SBS Digital News
※ Please note: This article was translated by AI and may contain errors.