What is the risk of tsunamis and floods for properties in coastal or low-lying areas?

Buying Property in JapanNatural Disaster RiskCoastal PropertyFlood RiskTsunami RiskLow-Lying Areas
Created At: 8/11/2025Updated At: 8/16/2025
Answer (1)

Okay, let's break down the tsunami and flood risks of buying property in coastal or low-lying areas in Japan. This is definitely one of the top concerns for many people, especially us foreigners, when buying property here.

Question Title: How Significant Are the Tsunami and Flood Risks When Buying Property in Coastal or Low-Lying Areas in Japan?

You've hit the nail on the head! This is absolutely the number one consideration when buying property in Japan, especially in coastal cities like Tokyo Bay, Osaka Bay, or Ise Bay. It's not that there's no risk, but you also can't just blanket say "don't buy coastal." The key lies in "the specific location" and "how well you understand and prepare for the risks."

Simply put, the risks fall into two main categories: Tsunami Risk and Everyday Flood Risk.

1. Tsunami Risk

The most familiar event for many is probably the massive tsunami triggered by the 2011 Great East Japan Earthquake – that scene was indeed shocking.

  • How Significant is the Risk?

    • This depends entirely on the geographical location. The Japanese archipelago is long, and the Pacific coast side is generally considered higher risk than the Sea of Japan side because large trench-type earthquakes occur more frequently along the Pacific plate.
    • However, this doesn't mean the Sea of Japan side is absolutely safe. There are historical records of earthquakes and tsunamis there too.
    • Core Point: The risk isn't about "yes or no," but "high or low." The closer you are to the coastline and the lower the elevation, the higher the risk level naturally is.

  • How to Assess It?

    • The Magic Tool: ハザードマップ (Hazard Map)
    • This is the single most important step! Every city and ward office (市役所 / 区役所) in Japan publishes this map on their official website. Just Google [Area Name] + ハザードマップ to find it.
    • This map clearly marks with different colors:
      • 津波浸水想定区域 (Tsunami Inundation Forecast Area): Where seawater would flood in the event of a major tsunami (e.g., a once-in-N-years event).
      • 最大浸水深 (Max Inundation Depth): How deep the flooding would be at its worst point – whether 0.5 meters or 3 meters, it's clear at a glance.
      • 避難場所 (Evacuation Shelters): Locations of emergency shelters are marked on the map.

    (This is a schematic; actual maps are more detailed)

    • When viewing a property, ask the agent directly: “この物件はハザードマップで津波浸水想定区域に入っていますか？” (Is this property within the tsunami inundation forecast area on the hazard map?) A responsible agent must answer truthfully.

2. Flood Risk (Flood Risk)

This risk is actually more "everyday" than tsunamis because it doesn't necessarily require a major earthquake; a single severe rainstorm can cause it.

  • Sources of Risk:

    1. River Flooding: If a property is very close to a major river (like the Arakawa or Edogawa in Tokyo) and in a low-lying area, be cautious about the risk of the river overflowing or breaching its banks during heavy rain.
    2. Internal Flooding (Inundation): Some areas aren't near rivers but are situated in low-lying "bowl-shaped" depressions. If rainfall is too intense and the drainage system can't cope, water accumulates on the surface – this is called "internal flooding." Parts of Tokyo's Setagaya Ward or Suginami Ward have this risk.
    3. Storm Surge: During typhoons, low atmospheric pressure and strong winds push sea levels up, causing seawater to inundate land. This is similar to a tsunami in effect but has a different cause. Coastal low-lying areas are particularly vulnerable.

  • How to Assess It?

    • Again, the Magic Tool: ハザードマップ (Hazard Map)
    • Flood risk maps are usually separate from tsunami maps, or are different layers on the same map. They show whether your area would flood in the event of a "100-year flood" (extreme rainfall event) and the estimated water depth.
    • Look at Place Names: Many Japanese place names reveal historical information. Names containing characters like “洼” (kubo, depression), “谷” (tani/ya, valley), “沼” (numa, marsh), “田” (ta/da, rice field), or “川” (kawa/gawa, river) often indicate areas that were historically wetlands or near water, meaning relatively low elevation. For example, Tokyo's "Shibuya" (渋谷) is named for its location within a valley.

To Summarize, What Should You Do? (Action List)

  1. Check! You MUST Check! ハザードマップ (Hazard Map)

    • This is essential homework when buying property in Japan. As soon as you have the address of a property you're interested in, the first thing to do is check this map. Be especially cautious about red and orange zones.

  2. Check the Elevation (海抜 - Kaibatsu)

    • Google Maps now shows elevation for many locations. Alternatively, search [Address] + 海抜. Generally, higher elevation is safer. For example, an area at 5 meters elevation near Tokyo Bay is vastly different in safety terms from one at 20 meters.

  3. Conduct a Site Visit

    • Walk around the neighborhood. Look for signs like “津波避難タワー” (Tsunami Evacuation Tower) or “海抜XXm” (Elevation XX meters). The more such signs there are, the more it indicates the area is officially recognized as a risk zone.
    • Check for large-scale disaster prevention infrastructure like seawalls, levees, or floodgates.

  4. Consult and Confirm

    • When purchasing, the real estate agent is legally obligated to present and explain the "Important Matters Explanation" document (重要事項説明書). This must include information on whether the property is located within a designated disaster hazard zone. Read it carefully and ask questions if anything is unclear.

  5. Consider Insurance

    • Standard Japanese Fire Insurance (火災保険) usually allows you to add Flood Damage Coverage (水災補償). If a property is in a risk zone but you really love it, make sure to get sufficient coverage with this rider. If disaster strikes, at least you'll have financial protection.

Final Advice

When buying property in Japan, finding a place with "zero risk" is almost impossible (earthquakes can happen anywhere). Properties in coastal and low-lying areas often offer great views, convenient access, and potentially more attractive prices.

Therefore, our strategy isn't to avoid them completely, but to: Understand the risks, Assess the risks, Manage the risks.

  • If the map shows your potential home is in an area with a "Max Inundation Depth of less than 0.5 meters," buying an apartment on the 2nd floor or higher might make it largely unaffected.
  • If it shows "Max Inundation Depth of 3-5 meters," you should probably think very carefully, or only consider high-rise apartments.
  • If it's a detached house (一戸建て) in such a zone, the risk is very real, requiring thorough mental and practical preparation (e.g., being ready to evacuate, purchasing comprehensive insurance).

Hope this information helps! Wishing you success in finding a home that's both desirable and safe!

Created At: 08-11 12:44:09Updated At: 08-12 02:54:23