"Where the front that brings the rain stays is becoming as important as how heavily it rains."
A joint research team from KAIST and the APEC Climate Center has found that the East Asian summer front has migrated north over the past half century, with the shift exceeding 200 km in late summer. This raises the risk that the Korean Peninsula will experience heavy rain and heat stress at the same time. The findings suggest that summer disaster planning should address flood prevention and heat-illness management together, through late September.
KAIST (President Choongsik Bae) announced on October 23 that a research team led by Professor Hyungjun Kim from the Department of AI and Futures Studies, who is also Director of the KAIST Institute for Climate, Environment and Energy, has identified the long-term northward migration of the East Asian summer front and the resulting increase in compound risk. The team conducted the study with Dr. Suyeon Moon and Dr. OkYeon Kim from the APEC Climate Center (APCC; Director Kyung-Ja Ha) by analyzing 47 years (1979 to 2025) of high-resolution reanalysis data.
Frontal precipitation accounts for about 40% of total summer precipitation in East Asia, and for about half in June and September. A front forms along the boundary between contrasting air masses, where temperature and moisture change sharply. The summer of 2024 illustrates what is at stake: Gunsan recorded an hourly rainfall of 131.7 mm, the highest on record, and more than 600 mm of rain fell over the Seoul metropolitan area in two days, while prolonged heat waves occurred during the same period.
The position of the front has received relatively little attention. Previous research has mainly examined changes in the intensity of frontal precipitation under global warming, and the research team also showed in earlier work that this intensity has increased. However, even a small shift in the position of a front can substantially change regional precipitation patterns and determine which communities face flooding and which swelter in the heat.
The team applied an automated front-detection algorithm to ERA5, a high-resolution (about 25 km) reanalysis dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF), and tracked the position of the front every six hours over the 47 years. After confirming that the detected fronts agreed well with front positions on weather maps, they found than throughout the summer, the front in the most recent period (2006 to 2025) was located farther north than in the earlier period (1979 to 1998).
The front moved north by about 213 km in late summer (September 10 to 30), compared with an average of about 146 km during the active frontal season (June 25 to July 15). In the earlier period, the late-summer front was located over the Yangtze River basin and the sea south of Jeju Island. In recent years, it has reached the southern Korean Peninsula. The shift is linked to a combination of factors, including warmer sea surface temperatures and changes in atmospheric circulation.
The northward migration also changed the spatial pattern of precipitation and heat stress. During the active frontal season, years with a northward-shifted front showed more precipitation in northern areas, including the Korean Peninsula, and greater heat stress in southern areas. The effect was stronger in late summer. In years when the front moved north, frontal precipitation increased substantially over the Korean Peninsula, and heat stress rose by more than 0.4°C at the same time. Heat stress was measured with the wet-bulb globe temperature (WBGT), an index that accounts for humidity as well as air temperature. A higher WBGT indicates hot, humid conditions in which sweat evaporates less readily, raising discomfort and the risk of heat stroke.
Wet and hot conditions also occurred together far more often in late-summer years with a northward-shifted front. Days on which both precipitation and heat stress were above normal levels occurred about 8 to 19 times more often in these years than in years when the front stayed in the south. The ratio remained significantly high, at about 3 to 9 times, even after the long-term trends were removed. This indicates that the result cannot be explained solely by separate increases in precipitation and temperature.
"This study shows that not only the intensity but also the position of fronts is changing, and as a result, the places and times at which rain and heat arrive are changing even within the same summer," said Professor Hyungjun Kim. He added that September has received little attention in summer disaster preparedness, and that a comprehensive adaptation strategy is needed to manage late-summer heavy rain and extreme heat together as a single compound risk.
The study was published in the international journal npj Climate and Atmospheric Science on . Dr. Suyeon Moon of the APEC Climate Center is the first author and a corresponding author, and Professor Hyungjun Kim of KAIST is a corresponding author.
Paper title: Recent change in northward migration of the East Asian summer front and increased compound wet–hot conditions (DOI: https://doi.org/10.1038/s41612-026-01570-x)
Authors: Suyeon Moon (APEC Climate Center, first and corresponding author), OkYeon Kim (APEC Climate Center), and Hyungjun Kim (KAIST, corresponding author)
This research was supported by the National Research Foundation of Korea's [AI-based Future Climate Technology Development] Program and by the Korea Meteorological Administration Research and Development Program "APEC Climate Center for Climate Information Services."
