What your agent must tell you about flood risk in Japan

Readout guide · Updated 2026-10-11

When you buy or rent a home in Japan, the agent must go through an explanation of important matters before you sign. Since 28 August 2020 that explanation includes flood risk. Here is what it covers and what it leaves out.

The rule

Before a contract is signed, a licensed agent explains the important matters about the property, the 重要事項説明じゅうようじこうせつめい (jūyō jikō setsumei). A change to the enforcement regulations of the Building Lots and Buildings Transaction Business Act (宅地建物取引業法たくちたてものとりひきぎょうほう) took effect on 28 August 2020 and added one more item: where the property sits on the municipality's water-hazard map. It applies to sales and to rentals.

Which map the agent must use

• The map is the one the municipality publishes under the Water Act (水防法すいぼうほう). It covers three kinds of flooding: river flooding (洪水こうずい), internal-water flooding when rain overwhelms the drains (雨水出水うすいしゅっすい) and storm surge (高潮たかしお).
• The agent should use the latest map available.
• Where a municipality has both an older planned-scale flood map and an assumed-maximum one, the assumed-maximum map is the one to show.
• If the municipality has not produced a map, the explanation records that.

Even outside the shaded area

If the property appears on the municipal map at all, the agent has to point out its approximate location, even when it sits outside the flood zone. In practice you will often be handed the map as an attachment (別紙べっし) with the spot marked on it.

What the rule does not do

• It requires disclosure, not a verdict. It does not ban sales or rentals in flood zones, and it does not say a property is safe or unsafe.
• The map decides the detail. You see what the municipal map shows, in that municipality's style. Legends differ, so read them. Tokyo, for example, publishes two river flood maps, so you may be shown either.
• It is not a depth guarantee for your building. A map gives an area's assumed water depth. It does not know whether your flat is on the third floor or in a semi-basement.

Questions to ask your agent

1. Which map is this, and from what date?
2. Is it the assumed-maximum map or the planned-scale one? Can I see both?
3. What depth does the map show at this address?
4. Does the municipality have a map for internal-water flooding and storm surge, and where is this property on them?
5. Is this home on the ground floor, in a semi-basement, or below street level? Where does the parking go?
6. Where is the nearest evacuation site, and which way would I go?
7. Is flood insurance available for this home, and what does it cover?

Cross-check it yourself

Before the explanation, you can look up the address on Readout. Paste it into the search box, or browse a town page such as Yoyogi or Kita ward in Osaka. Treat Readout as a screening tool. It shows the national river-flood layer at the assumed maximum, and some prefecture-managed rivers are missing from that layer. The municipal map is the one your agent must show you, and the one to rely on.

To learn to read the colours, see how to read a Japanese hazard map.

More guides

• How to read a Japanese hazard map, in English
• Earthquake intensity 6-lower and Japan's building codes

Sources

• Nagano Prefecture, 不動産取引時の重要事項説明における水害リスクに係る説明義務について
• Hazard Map Portal Site (ハザードマップポータルサイト), MLIT and GSI

Readout repackages public Japanese government data for screening. It is not engineering, insurance or legal advice.