Rainfall intensity per hour is a more critical indicator of immediate danger than the total amount of rain fallen, YTN News said.
Understanding these thresholds is vital for public safety because rapid accumulation of water can lead to sudden flooding and life-threatening conditions. While a total rainfall figure may seem manageable over a day, the speed at which that water falls determines whether infrastructure can drain it or if it will overflow.
YTN reporter Choi A-young said that even moderate intensity can disrupt daily activities. When rainfall reaches 15 mm per hour, windshield wipers must run continuously, and water begins to pool on roads [1].
As the intensity increases, standard protective measures become ineffective. Choi said that once rainfall exceeds 30 mm per hour, using an umbrella becomes meaningless [2]. This level of precipitation significantly reduces visibility and complicates travel.
Severe risk is associated with a benchmark of 50 mm per hour [3]. Choi said that there is a fundamental difference between 50 mm of rain falling over an entire day and the same amount pouring down within a single hour [4]. The latter creates an immediate risk of flash flooding and structural failure.
Extreme weather events have already manifested in the region. Last year, 15 locations across South Korea experienced extreme hourly rainfall of 100 mm or more [5]. Such events are particularly dangerous in the southern regions of the country, where heavy rain can trigger rapid landslides or urban flooding.
Public safety officials advise residents to monitor hourly rates rather than daily totals to determine when evacuation may be necessary. The ability to recognize these specific thresholds can mean the difference between a safe shelter and a dangerous situation during a storm.
“Once rainfall exceeds 30 mm per hour, using an umbrella becomes meaningless.”
The shift in focus from total accumulation to hourly intensity reflects a growing need for granular weather data in disaster prevention. By educating the public on specific thresholds—such as the 30 mm and 50 mm markers—authorities aim to reduce casualties by encouraging proactive evacuation before drainage systems are overwhelmed by extreme bursts of rain.
