"Obocheong? Gasangcheong?" Why Climate Forecasting Is More Difficult During the Monsoon Season

Average Annual Precipitation Accuracy 91%
Accuracy Noticeably Drops from June to August
KMA: "Data Shortage, Abnormal Heat, and Other Practical Issues"

On the 13th, when the monsoon rain fell nationwide, commuters hurried their steps at the Gwanghwamun intersection in Seoul. / Photo by Mun Ho-nam munonam@

[Asia Economy Intern Reporter Seohee Lee] The Korea Meteorological Administration (KMA), which has struggled annually with the notorious nicknames like ‘Obocheong’ and ‘Gasangcheong,’ is once again having a hard time predicting precipitation this year.

On the evening of the 20th, the KMA forecasted that the monsoon rain would fall nationwide overnight and gradually stop from the metropolitan area by dawn on the 21st. However, when the monsoon rain did not cease by the morning of the 21st, the forecast at 5 a.m. was revised to "occasional rain in the metropolitan area, Chungnam region, Jeolla region, Gyeongnam region, and Jeju Island mountain area until morning (06:00?12:00), in Gangwon Yeongseo, Chungbuk, and Gyeongbuk region until night (18:00?24:00), and in Gangwon Yeongdong until early morning tomorrow (00:00?06:00)."

On the 8th as well, the KMA predicted that the entire country would be under the influence of the monsoon front. It forecasted about 30?100 mm of rain in the metropolitan area and Gangwon Province, and heavy rain exceeding 150 mm in northern Gyeonggi and northern Gangwon regions. However, only about 2 mm of rain fell in Seoul over two days, and about 3 mm was observed in northern Gyeonggi, leaving citizens anxious about the monsoon rain feeling disappointed.

Additionally, the KMA faced public criticism for inconsistent weather forecasts, such as predicting rain the day before but changing the forecast to ‘cloudy’ on the day itself.

◆ ‘Forecast Accuracy’ Drops Especially from June to August

The KMA’s weather forecasts tend to miss the mark particularly during the monsoon season. According to the ‘precipitation accuracy’ and ‘precipitation hit rate’ provided by the Meteorological Administration’s official website, the KMA’s precipitation predictions show a notably lower accuracy rate between June and August.

Photo provided by the Meteorological Administration website

Precipitation accuracy is an indicator expressed as a percentage (%) that shows how much the weather forecast by the KMA matches the actual observed weather afterward. For example, it represents the combined rate of cases where the KMA predicted ‘rain’ and it actually rained, or predicted ‘no rain’ and it indeed did not rain.

When calculating precipitation accuracy from June last year to May this year using this method, the average accuracy reaches 91%. The period to pay attention to is the monsoon season from June to August. Although the average accuracy exceeds 90%, the accuracy in July and August was only 83% and 80%, respectively. This indicates that climate prediction during the monsoon season is relatively difficult.

◆ Why Is Climate Prediction Difficult During the Monsoon Season?

On the 18th, when a shower fell, citizens in Seoul hurried on their way to work. The Korea Meteorological Administration forecasted that there would be occasional clouds nationwide and some places would experience showers. Photo by Kim Hyun-min kimhyun81@

The reason climate prediction is difficult during the monsoon season is due to showers. Summer showers can vary significantly even with the same conditions, depending on slight changes in atmospheric conditions.

The problem is that it is practically impossible for the KMA to accurately observe the entire state of the atmosphere. Currently, the KMA conducts ground weather observations using 96 Automated Surface Observing Systems (ASOS) nationwide, including the Seoul Meteorological Observatory, and 533 Automated Weather Stations (AWS) for disaster prevention. Combining ASOS and AWS, there is approximately one observation station every 10 km.

Park Jeong-min, spokesperson for the KMA, said that the observation stations installed every 10 km are not sufficient to represent the entire atmospheric state. Park explained, “Because observation stations are installed at intervals of more than 10 km, forecasts can vary depending on where the stations are located. This is especially critical during the monsoon season, where even small factors have a significant impact on predictions.” He added, “Moreover, since the atmospheric thickness reaches about 12 km, it is difficult to accurately observe the atmospheric state with the current observation data.”

Another issue is that global warming and abnormal high temperatures have made the weather more unpredictable than before. The patterns of low pressure and atmospheric instability have become more diverse, making predictions harder. Park said, “Even for the same monsoon, recent monsoons are much more irregular than before. These are patterns we have not seen previously.”

The geographical characteristics of the Korean Peninsula also contribute to the difficulty in climate prediction. Park said, “Korea is surrounded by the sea on three sides, and 70% of the land is mountainous. It is an environment that absorbs moisture from all directions, causing high variability, which makes climate prediction more difficult than in Japan or China.”

This content was produced with the assistance of AI translation services.