Record-breaking rainfall hammered the Tokyo metropolitan area on August 13 and 14, 2026, turning streets into rivers, flooding homes and paralyzing transport in one of Japan’s most densely populated regions.
The heaviest downpours struck Chiba Prefecture, just east of Tokyo, where more than 360 mm of rain fell in just 12 hours – roughly three times the average monthly rainfall for August.
At least four people have died and one remains missing, while thousands were stranded overnight at Narita Airport and major train stations as services were suspended.
Authorities issued the highest-level heavy rain warning for parts of Chiba for the first time, ordering more than 100,000 residents to evacuate as rivers swelled and roads disappeared under floodwaters.
What Caused the Deluge
The extreme rainfall was driven by a combination of warm, humid air flowing into eastern Japan and colliding with cold air aloft, creating highly unstable atmospheric conditions.
The Japan Meteorological Agency (JMA) said moisture from a weakening tropical depression – formerly Typhoon No. 15 “Chan-hom” – fed into the system, while easterly and northeasterly winds converged near Chiba, repeatedly triggering intense rain clouds over the same areas.
This setup produced what meteorologists call a “linear precipitation zone”: a narrow band of storm cells that remain almost stationary for hours, dumping enormous amounts of rain on a limited area.
In Chiba City and Sakura, hourly rainfall reached 115 mm and 97 mm respectively – both record-breaking rates for those locations.
How Much Rain Fell
The numbers are staggering even by Japan’s standards:
– Chiba City recorded 348 mm of rain in the 12 hours leading up to 1:40 a.m. on August 14, a new local record.
– Some areas of Chiba received around 100-120 mm in a single hour, with 24-hour totals reaching 366.5 mm at certain observation points.
– The 12-hour total of about 360 mm in parts of the prefecture is roughly equivalent to three months’ worth of rain falling in half a day.
By comparison, Tokyo typically receives about 161 mm of rain over the entire month of August.
Damage and Disruption
The human and economic toll is still being assessed, but early figures point to significant disruption:
– At least four people were confirmed dead in Chiba, including a man found floating in a flooded road in Ichikawa and a woman trapped in a submerged car in Sakura.
Another person pulled from a flooded car in Kashiwa was presumed dead, and one more person remained missing.
– Around 7,000 passengers were stranded overnight at Narita Airport as trains and buses connecting the airport to Tokyo were suspended. Thousands more spent the night at Soga train station and other transit hubs.
– More than 80 homes were flooded in Chiba, with nearly 230,000 residents advised to take shelter at various points. Power was knocked out to about 68,000 households at the peak, falling to around 23,000 by Friday morning.
– Roads, railways and local infrastructure were inundated, with footage showing cars submerged in floodwaters and muddy water pouring into residential areas.
The flooding occurred during the Obon holiday period, one of Japan’s busiest travel weeks, amplifying the disruption for both residents and international visitors.
How This Compares to Japan’s Worst Rain Events
Japan is no stranger to extreme rainfall, but the Chiba event ranks among the most intense short-duration deluges in recent history for the Tokyo region.
Historically, the country’s heaviest recorded rains have been associated with stalled rain fronts, typhoons and “linear precipitation zones” similar to the one seen this week.
Some of the most significant rain disasters in Japan include:
– July 2018 Heavy Rains (Heisei 30): Successive downpours across southwestern Japan killed at least 179 people, the deadliest rainfall disaster in decades. Some areas in Shikoku received more than 1,800 mm of rain over 10 days, with multiple locations recording their highest one-hour and three-day totals on record.
– Typhoon Hagibis (October 2019): One of the most destructive typhoons in modern Japanese history, Hagibis brought more than 1,000 mm of rain to Hakone in Kanagawa Prefecture over three days. The JMA recorded 922.5 mm in a single day at Hakone – the highest one-day total ever observed in Japan.
– July 2020 Kyushu Floods: Record-breaking rain hit Kumamoto and Kagoshima prefectures, with hourly rates exceeding 100 mm and rivers overflowing across the region. The event was officially designated as the “Heavy Rain of July, Reiwa 2” and caused dozens of deaths and widespread damage.
– July 2021 and 2023 Rain Events: In 2021, western Japan, especially northern Kyushu, saw more than 1,000 mm of rain in eight days in some areas. In 2023, a stalled seasonal front and typhoons triggered record rainfall in Tohoku and Hokuriku, with multiple observation points recording their highest hourly and 24-hour totals.
– September 2024 Ishikawa Flooding: In earthquake-hit Ishikawa Prefecture, Wajima recorded 121 mm of rain in one hour, the heaviest rainfall there since records began in 1921, triggering landslides and life-threatening flooding.
Compared to these events, the Chiba rainfall is notable for its extreme intensity over a very short period in a heavily urbanized area near Tokyo, rather than for multi-day totals. The 348 mm in 12 hours in Chiba City and hourly rates above 100 mm place it among the most severe localized rain events in the region’s recorded history.
Sources:
– Al Jazeera, “Record rainfall leaves four dead, thousands stranded in Japan,” August 14, 2026. (aljazeera.com)
– BBC, “Japan floods: three die as island hit by ‘heaviest’ rainfall,” July 11, 2023. (bbc.com)
– BBC, “Japan flood: At least 179 dead after worst weather in decades,” July 11, 2018. (bbc.com)
– Chosun Biz (English), “Record rains in Chiba kill 4 and strand 7,000 at Narita Airport,” August 14, 2026. (biz.chosun.com)
– Government of Japan, White Paper on Disaster Management, various years (2018-2024). (https://www.bousai.go.jp/en/documentation/white_paper/pdf/SF1-1.pdf )
– ITV News, “Four killed in Japan after record-breaking rainfall floods homes and roads,” August 14, 2026. (itv.com)
– Phys.org, “Heavy rain soaks eastern Japan, prompting highest-level warning,” August 13, 2026. (phys.org)
– The Guardian, “Weather tracker: Extensive flooding in Japan after ‘unprecedented’ rainfall,” September 23, 2024. (theguardian.com)
– The Jakarta Post, “Thousands stranded as heavy rain kills at least four in Japan,” August 14, 2026. (thejakartapost.com)
– Xinhua, “Death toll rises to 8 after record rain batters Japan’s Chiba Prefecture,” August 14, 2026. (english.news.cn)
– en.wikipedia (wikipedia.org)
– bousai.go – (https://www.bousai.go.jp/en/documentation/white_paper/pdf/2024/05_Chapter3.pdf)
