Both Tokyo and Osaka are seaside cities with a number of large and small rivers, which makes them vulnerable to flooding after heavy rains.

Local government websites have hazard maps that demarcate the areas most likely to flood, especially when major rivers overflow. Unfortunately, for people who don’t read Japanese, only  few of the local maps are in English.

In general, dark blue denotes areas most likely to flood. However, the color legend of the maps does vary from ward to ward so if you can’t read Japanese, please note the numbers of water height to gauge the water-level legend or ask a Japanese speaker to help you.

When severe weather conditions occur, it’s recommended that you check the official advisories and warnings on Japan Meteorological Agency website. 

For a detailed map of other regions, see the hazard map portal of the Japan’s transportation ministry.

Hazard maps of Tokyo

Chiyoda Ward 千代田区

• Standard map
• If Arakawa River (荒川) overflows

Chuo Ward 中央区

• If Sumidagawa River (隅田川), Kandagawa River (神田川) and Nihonbashigawa River (日本橋川) are flooded
• If Arakawa River overflows

Minato Ward 港区

• English version available

Shinjuku Ward 新宿区

Bunkyo Ward 文京区

Taito Ward 台東区

• English version

Sumida Ward 墨田区

• English version (two pages: 1 2)

Koto Ward 江東区

Shinagawa Ward 品川区

Meguro Ward 目黒区

Ota Ward 大田区

• If Nomigawa River (呑川), Uchikawa River (内川) and Marukogawa River (丸子川) overflow
• If Tamagawa River (多摩川) overflows

Setagaya Ward 世田谷区

• Standard map
• If Tamagawa River (多摩川) overflows

Shibuya Ward 渋谷区

Nakano Ward 中野区

• Standard map
• If Kandagawa River (神田川) overflows

Suginami Ward 杉並区

Toshima Ward 豊島区

Kita Ward 北区

• If Arakawa River (荒川) overflows
• If Sumidagawa River (隅田川), Shingashigawa River (新河岸川), Shakujiigawa River (石神井川) and Kandagawa River (神田川) overflow

Arakawa Ward 荒川区

Itabashi Ward 板橋区

• If Arakawa River (荒川) overflows
• If Shingashigawa River (新河岸川), Shakujiigawa River (石神井川) and Shirakogawa River (白子川) overflow

Nerima Ward 練馬区

• Standard map
• If Kandagawa River (神田川) overflows

Adachi Ward 足立区

• In the case of severe rainfall
• If Tonegawa River (利根川) overflows
• If Edogawa River (江戸川) overflows
• If Arakawa River (荒川) overflows
• If Nakagawa River(中川), Ayasegawa River (綾瀬川), Shibakawa (芝川) and Shinshibakawa (新芝川) overflow

Katsushika Ward 葛飾区

Edogawa Ward 江戸川区

• If the case of severe rainfall
• If Edogawa River (江戸川), Tonegawa River (利根川) and Arakawa River (荒川) overflow

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Hazard maps of Osaka

Kita Ward 北区

Miyakojima Ward 都島区

Fukushima Ward 福島区

Konohana Ward 此花区

Chuo Ward 中央区

Nishi Ward 西区

Minato Ward 港区

Taisho Ward 大正区

Tennoji Ward 天王寺区

Naniwa Ward 浪速区

Nishi-Yodogawa Ward 西淀川区

Yodogawa Ward 淀川区

Higashi-Yodogawa Ward 東淀川区

Higashinari Ward 東成区

Ikuno Ward 生野区

Asahi Ward 旭区

Joto Ward 城東区

Tsurumi Ward 鶴見区

Abeno Ward 阿倍野区

Suminoe Ward 住之江区

Sumiyoshi Ward 住吉区

Higashi-Sumiyoshi Ward 東住吉区

Hirano Ward 平野区

Nishinari Ward 西成区