Southern regions of South Korea face forecasts of extreme rainfall reaching up to 80 mm per hour [5] over the upcoming weekend and public holidays.

Understanding the specific intensity of hourly rainfall is critical for public safety because the risk of flash flooding and infrastructure failure increases sharply as the rate of precipitation rises.

Reporter Choi Ah-young of YTN said how different levels of hourly rainfall translate into immediate physical dangers. According to the report, a rainfall intensity of 15 mm per hour causes windshield wipers to run continuously and water to begin pooling on roads [1].

As the intensity increases, the ability to navigate the outdoors diminishes. Choi said that when rainfall exceeds 30 mm per hour, using an umbrella becomes ineffective [2].

Risk levels escalate further as the volume of water exceeds drainage capacities. Rainfall intensity over 50 mm per hour sharply raises the risk of flooding [3]. Once the intensity surpasses 70 mm per hour, the weather is classified as "extreme rain," at which point flood damage becomes a realistic threat [4].

"When it exceeds 70mm per hour, it becomes 'extreme heavy rain,' and flooding damage becomes a reality," Choi said.

The warnings come as officials urge residents in the southern regions to prepare for potential flooding. The focus on hourly rates rather than total daily accumulation highlights the danger of rapid-onset flooding that can trap commuters and residents in low-lying areas.

Choi said that even at 15 mm per hour, wipers move without rest and water collects on the roads [1]. This progression from manageable rain to extreme weather occurs rapidly during the types of storm systems expected this month.

“Rainfall intensity over 70 mm per hour is classified as ‘extreme rain’ with realistic flood damage.”

By shifting the public focus from total rainfall volume to hourly intensity, South Korean authorities are emphasizing the speed of water accumulation over time. Because drainage systems have a fixed capacity, the 'extreme rain' threshold of 70 mm per hour represents a tipping point where urban infrastructure can no longer divert water, leading to immediate and severe flooding regardless of the total storm duration.