NAGOYA, Japan - Record-breaking torrential rain brought parts of Nagoya to a standstill on September 8, flooding roads and transport infrastructure as more than 100 millimetres of rain fell within a single hour.

Nagoya recorded 104.5 mm of rainfall in the hour ending at around 5 p.m., the highest hourly rainfall reported in the city’s observational history. The previous record was associated with the catastrophic Tokai Heavy Rain of September 2000.

The extreme downpour developed as linear rainbands formed over Aichi and neighbouring Gifu Prefecture, repeatedly directing intense rainfall over the same areas. Such systems can produce dangerous accumulations within a short period and leave little time for urban drainage networks to respond.

Roads and Transport Overwhelmed

Floodwater rapidly spread across parts of Nagoya during the evening rush hour. Roads were submerged, vehicles became stranded and water surged from manholes as drainage systems struggled with the intensity of the rainfall.

Near Chikusa Station, floodwater reached railway tracks, while commuters across the city faced severe disruption as services were halted.

The Nagoya Municipal Subway suspended operations across all lines from around 5:15 p.m., while city buses were also taken out of service across the network. Subway services began gradually resuming later that night, but buses remained suspended for the rest of September 8.

Other rail services were affected as the extreme weather disrupted movement through one of central Japan’s most important transport hubs. The Tokaido Shinkansen also faced temporary disruption linked to the heavy rain.

Highest-Level Flood Warning Issued

The Japan Meteorological Agency issued a Level 5 flood special warning for the Shonai River, which flows through Aichi and Gifu prefectures.

Level 5 is the highest category on Japan’s five-level disaster warning system and indicates that a life-threatening situation may already be occurring. Authorities urged people in threatened areas to immediately secure their safety and move to higher or safer locations where evacuation remained possible.

Across Aichi and Gifu prefectures, 41 people were reported injured as torrential rain caused flooding in several areas.

The flooding also reached facilities being prepared for the Asian Games, which are scheduled to open in Nagoya on September 19. Around 400 athletes and staff were temporarily evacuated to higher ground, although city officials said the flooding was not expected to prevent the Games from going ahead.

When an Hour of Rain Becomes an Urban Emergency

Nagoya’s flooding illustrates a growing challenge for highly urbanised cities: extreme rainfall does not need to last for days to become dangerous.

When extraordinary amounts of water fall within an hour, paved surfaces offer little opportunity for absorption and drainage networks can be overwhelmed faster than water can be carried away. Roads, railway lines, underground stations, tunnels and basements can then become points of particular vulnerability.

Climate science has established that a warmer atmosphere is capable of holding more moisture, creating conditions that can intensify heavy rainfall. However, the influence of climate change on any individual storm requires event-specific analysis.

What is already clear from Nagoya is the scale of the challenge posed by short-duration rainfall extremes.

A rainfall benchmark that had stood since the destructive 2000 Tokai Heavy Rain has now been surpassed.

For cities adapting to a changing climate, the question is increasingly not only how much rain may fall over a day, but how much can arrive in a single hour and whether urban infrastructure is prepared for it.