Geoje, South Gyeongsang Province, recorded 116.8 mm of rain per hour early Monday morning [1].

The event triggered a new "disaster rain" emergency alert system designed to warn residents when precipitation intensity reaches critical levels. This system prioritizes rainfall intensity over total accumulation because rapid water buildup significantly increases the immediate risk of flash floods and landslides.

Emergency alerts for "disaster rain" are issued when rainfall reaches or exceeds 100 mm per hour [2]. This represents the highest level of warning, surpassing the standard heavy rain emergency alert which is issued at 72 mm per hour [3]. During the overnight storm in Geoje, these high-level alerts were sent four times [1].

"Today early morning in Geoje, Gyeongnam, 116.8 mm of rain poured down per hour," a YTN anchor said [4].

Public safety officials use these markers to categorize risk. While 15 mm per hour is the threshold where vehicle windshield wipers typically begin continuous operation, levels exceeding 30 mm per hour generally necessitate the use of umbrellas [5, 6]. However, the risks escalate quickly as intensity increases. The 100 mm per hour threshold is considered a critical danger zone [2].

Data indicates these extreme events are becoming a point of focus for South Korean disaster management. Last year, 15 different regions across the country experienced rainfall exceeding 100 mm per hour [7].

"It is sent when the hourly precipitation is 100 mm or more," the YTN anchor said [8].

The current alert system aims to provide a clearer hierarchy of danger. The anchor said that the disaster rain alert is a "higher level of the highest warning" compared to the 72 mm per hour emergency alerts [9].

“Geoje recorded 116.8 mm of rain per hour early Monday morning.”

The implementation of a specific 'disaster rain' alert for precipitation exceeding 100 mm per hour reflects a shift in South Korean emergency management. By distinguishing between general heavy rain and extreme intensity, authorities can more accurately signal when infrastructure is likely to be overwhelmed, moving away from total rainfall metrics which may mask the danger of a sudden, violent burst of rain.