Tokyo flood risk: how to check any address, in English

Tokyo is not uniformly safe or uniformly risky — flood exposure changes street by street. Here is how Japan's official flood assumptions work, what the numbers actually mean at living height, and how to check a specific address without reading Japanese.

Sources: MLIT/GSI "Overlay Hazard Map", Tokyo municipal shelter policies. Reference information, not advice.

The eastern lowlands: where the numbers get serious

Much of eastern Tokyo — along the Arakawa and Edogawa rivers — sits on low-lying former wetland, in places below sea level. Official maximum-scale flood assumptions there commonly show depths of 0.5–3.0m, and 3.0m or more near the rivers. As a verified example from our own pipeline: a point near Tokyo Skytree (Oshiage, Sumida ward) shows an assumed depth of 0.5–3.0m, with floodwater expected to take 1–3 days to recede.

Western Tokyo, on the Musashino upland, is a different story — most addresses there sit outside river-flood zones entirely. This is why checking the specific address matters more than the city's reputation.

How to read the depth colors

Japanese hazard maps color-code assumed flood depth. Three heights are worth memorizing: 0.5m ≈ above floor level (damage to walls, wiring, water heater begins), 3m ≈ up to the first-floor ceiling (first floor unusable), 5m ≈ the second floor. Also note there are two assumption levels: maximum scale (roughly a 1-in-1000-year rainfall — plan for this) and planned scale (more frequent events). Most published maps now show the maximum scale.

The shelter caveat most people miss

In parts of eastern Tokyo, designated shelters carry an operating condition: they do not open when major river flooding is imminent. Municipalities there instead call for wide-area evacuation — leaving for other districts early, while trains still run. If you live in (or are buying in) the eastern lowlands, "I'll just walk to the nearby school" may not be the plan. Always check the municipality's own shelter list.

Check your address (free)

mamoie's free checker assesses six hazards (flood, earthquake, landslide, tsunami, storm surge, liquefaction) for any Japanese address using official government data. The interactive UI is in Japanese (it works with any address pasted in), and developers can get English JSON from our free API with ?lang=en.

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