How to read Japanese hazard maps before you move — 5 practical steps

When choosing a place to live in Japan, most people carefully compare layout, rent, and commute time — but few dig into the disaster risk of the land itself. Yet, just 20 minutes with the hazard maps published by Japan's Ministry of Land, Infrastructure, Transport and Tourism (MLIT) is enough to make flood, landslide, liquefaction, and tsunami — the four major risks — largely visible.

This article walks through how to read Japanese hazard maps in five practical steps, whether you are renting or buying. Every dataset referenced here is published free of charge by public institutions.

Why you should check hazard maps before moving in

Water-related disasters in Japan have grown more severe almost every year. Since the 2018 West Japan floods, fire-insurance premiums have kept rising nationwide. Real-estate market data shows that properties inside projected inundation zones don't just pay higher premiums — their long-term asset value also tends to erode. The same holds for landslide caution zones: real-estate brokers are legally required to disclose them as material information at contract signing.

In other words, a hazard map isn't only about the person moving in today — it's also about risk that comes back to bite you when you sell or move again several years later. Twenty minutes before signing is a bargain compared to the cost of regret.

Step 1: Read the flood inundation map

Start with the flood inundation area. On MLIT's "Overlay Hazard Map" (Kasaneru Hazard Map) at disaportal.gsi.go.jp, enter an address and the projected maximum inundation depth is color-coded on the map.

• Below 0.5m (yellow): Below-floor flooding possible; recovery is relatively easy.
• 0.5–3.0m (orange to red): Above-floor flooding is essentially certain; first-floor living should be avoided.
• Above 3.0m (dark red to purple): Second floors may be reached; the building may become fully unusable.

Even inside a zone, also check the "inundation duration" layer. An area projected to remain inundated for "one week or longer" after a river-overflow means that if you time evacuation wrong, you can't return home for a week.

Step 2: Check the landslide caution zones

For any property near a slope or a valley, verify designation as a Landslide Caution Zone (commonly called the "yellow zone") or a Special Landslide Caution Zone (the "red zone"). Both are visible on the same Overlay Hazard Map.

Red zones are areas where structural damage to buildings is projected. Under the Building Lots and Buildings Transaction Business Act, brokers are legally obligated to disclose this in the material-information notice, so it should appear in the contract. That said, rental contracts sometimes handle this in more abbreviated form — checking the official map with your own eyes is safer.

Even if you live in a flat urban area, your commuting route can pass through landslide caution zones more often than you'd expect. It's worth checking not just the house but whether disaster could cut off your access route — verify along the entire commute path.

Step 3: Look at liquefaction risk

Soil liquefaction is a phenomenon where the ground turns into a water-saturated sand-like state during an earthquake, causing buildings to tilt. Risk is especially high on reclaimed land, along rivers, and along coastlines. You can find the "liquefaction map" on each prefecture's hazard portal.

Look at the color coding for "liquefaction likelihood" and any ground judgment values (such as the PL index). In areas classified as "high likelihood," even standard two-story wooden houses have been reported tilting by tens of centimeters — as documented after the 2011 Great East Japan Earthquake.

Liquefaction publication granularity varies by municipality, so the disaster-prevention portal of the specific city or ward is the most reliable source. Some areas are also partially covered on MLIT's Overlay Hazard Map.

Step 4: Tsunami inundation (for coastal areas)

If you live within roughly 5 km of the coast, you must check the tsunami inundation projection. The "tsunami" layer of the Overlay Hazard Map color-codes projected maximum inundation depth and arrival time.

Three things to verify: (1) projected inundation depth vs. your floor level, (2) distance to the nearest tsunami-evacuation building or high ground, and (3) projected arrival time. For example, "5 m projected depth, 15 minutes arrival, 12 minutes on foot to high ground" means the whole family must be ready to evacuate immediately after the shaking stops — pre-verify the route.

Step 5: Check historic disaster records

Hazard maps are "projections." Historic disaster records are "actuals." On the Geospatial Information Authority of Japan's (GSI) map portal at maps.gsi.go.jp, you can overlay Meiji-era former river courses, reclaimed land distribution, and traces of past flooding.

Specifically, the following are worth checking:

• Former river courses and former ponds/swamps: Reclaimed swamps and old river beds have poor drainage — liquefaction and inundation risk stack on top of everything else.
• Disaster history monuments: Stone markers commemorating past flood or landslide lessons. GSI's map shows them as a natural landmark icon.
• Flood Landform Classification Map: Terrain categories such as flood plains, natural levees, and back-marshes. Lets you judge topographic risk at a glance.

After the five steps

By now you should have a full picture of the physical disaster risks of the land itself. From here, you combine that with other location factors — vacancy rate, land-price trend, daily convenience, and long-term prospects — to reach a total judgment.

SafeLand's location assessment integrates the hazard information above with population dynamics from e-Stat and transaction prices from Reinfolib, then returns a grade from A to D. Use it as a cross-check to the question "OK, but how does this neighborhood look overall?" — right after you've read the hazard maps.