Climate Change Pushes East Asia’s September Rain Front 213 Kilometers North

A major East Asian weather front now remains much farther north in September than it did in past decades, helping extend summerlike heat and heavy-rain risks deeper into early autumn, according to a joint study by South Korean climate researchers.

Researchers from the APEC Climate Center and the Korea Advanced Institute of Science and Technology found that the center of the front during Sept. 10-30 shifted north by about 1.92 degrees of latitude, or approximately 213 kilometers, when recent conditions were compared with an earlier period. That distance is roughly comparable to the straight-line distance between Seoul and Daegu.

The study, published in the international journal npj Climate and Atmospheric Science, examined European Centre for Medium-Range Weather Forecasts ERA5 reanalysis data covering 47 years from 1979 through 2025. The researchers compared the front’s position in 2006-2025 with its position in 1979-1998.

A weather front forms where air masses with different temperatures and moisture levels meet. In East Asia, the boundary can channel hot, humid air northward. As that moisture rises, it can generate large rain clouds and intense downpours. The same humid conditions can also hinder the evaporation of sweat, making it harder for the human body to cool itself and increasing heat stress.

The analysis found that the front also moved north during the traditional monsoon period from late June to mid-July, but by a smaller amount. Its recent monsoon-season position was about 1.32 degrees of latitude, or roughly 146 kilometers, north of where it was in the earlier period. The larger shift in mid-to-late September suggests that the seasonal retreat of summer conditions has changed more sharply in early autumn.

Traditionally, the front advances toward the Korean Peninsula during summer and moves south once colder winds arrive in September. The study indicates that this southward retreat is now occurring later or less completely, leaving Korea and neighboring parts of East Asia exposed to warm, moisture-laden air for longer.

The researchers also examined wet-bulb globe temperature, an index that combines air temperature, humidity and sunlight to estimate the heat stress people actually experience. Their results showed that the northward displacement of the September front has increased the risk of oppressive heat and concentrated rainfall occurring at the same time.

Moon Su-yeon of the APEC Climate Center said disaster-response systems should reflect the fact that climate change is allowing summer hazards to persist later in the year. She called for integrated planning that prepares communities for both extreme heat and heavy rain rather than treating the two threats separately.