Chiba Hit by Record 360mm Rain in 24 Hours; Level 5 Warning Issued August 13

Chiba Prefecture experienced record-breaking rainfall on August 13, 2026, with more than 360 millimeters falling in 24 hours. Japan’s Meteorological Agency issued Level 5 emergency warnings for 19 municipalities, the nation’s highest alert level. Four deaths were confirmed, over 45,000 households lost power, and approximately 7,000 travelers were stranded at Narita Airport as flooding disrupted transport and infrastructure across the region.

How the rainfall unfolded

Linear precipitation bands developed around 6 p.m. on August 13, concentrating extreme rainfall over the same areas for hours. In Chiba city, hourly precipitation reached 115 millimeters, roughly equal to the area’s typical August monthly rainfall. Chiba, Kashiwa, and Yachiyo each recorded hourly rainfall exceeding 100 millimeters. The Japan Meteorological Agency warned of extremely unstable atmospheric conditions as warm, humid air collided with cold upper-level air, creating dangerous conditions for flash flooding and landslides.

Flooding and infrastructure collapse

Roads across Chiba transformed into fast-moving torrents. In Matsudo and Ichikawa, floodwater rose halfway up vehicle bodies, trapping drivers. At one underpass near Chiba Prefectural Police headquarters, water reached waist height. Buses had water enter their cabins, forcing passengers to move to upper levels. More than 360 millimeters of rain fell in 24 hours, inundating roads and railways during one of Japan’s busiest holiday weeks. Train services on the JR Keiyo Line and other routes were suspended.

Deaths, power outages, and evacuations

Four deaths were confirmed by August 14 morning, including one person trapped in a submerged vehicle. Another person remained missing. More than 45,000 households experienced power outages at peak, with 22,000 still without electricity by 11 a.m. on August 14. Evacuation orders temporarily affected more than 400,000 people. Over 500 people sought shelter at the Chiba Prefectural Government building. Chiba Governor Toshihito Kumagai stated: ‘This case was an extremely unusual situation. I have responded to many disasters in the past, but I have never experienced a case like this.’

Narita Airport and transport disruption

Approximately 7,000 travelers were stranded at Narita Airport on August 14 as flooding in surrounding areas disrupted ground transport. Hundreds of passengers spent the night under foil blankets at terminal evacuation centers, collecting blankets, water bottles, and snacks from airport staff. Japan Airlines reported some flights may experience delays but no cancellations were expected. All flights were scheduled to operate normally on August 14. Several major highways in Chiba were shut, forcing drivers onto alternative routes and causing heavy congestion.

Final Thoughts

The August 13 rainfall marked an unprecedented disaster for Chiba Prefecture, with record 360mm accumulation triggering Japan’s highest emergency alert. The combination of four confirmed deaths, mass power outages, and transport chaos underscores the severity of linear precipitation bands when they stall over populated areas.

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