Japan publishes some of the best natural-hazard mapping in the world, and it is free. The problem for a foreign buyer is that the main portal is in Japanese and assumes you know what the colours and terms mean. This walkthrough explains, in plain English, how to read the flood, landslide, and tsunami information for a specific house, so you can check a plot yourself before you fall for it.
What is the Japanese hazard map portal?
The main national portal is the hazard map site run by Japan's Geospatial Information Authority (GSI), known as disaportal. It overlays official government hazard data (flood, landslide, tsunami, and more) on a map, so you can search an address or point and see which risks apply there. It is authoritative and free, though the interface is in Japanese.
You can reach it at the MLIT and GSI hazard map portal (disaportal). It offers a "layered" hazard map that stacks several risk types on one view, and links out to individual municipalities' own hazard maps. For a buyer, the layered map is the quickest way to see, for one plot, whether it sits in a flood, landslide, or tsunami zone at the same time.
How do I read the flood layer?
The flood layer shades areas by expected inundation depth under a design storm, using colour bands. The standard bands run roughly from shallow (under half a metre) through intermediate depths (about half a metre to three metres, and three to five metres) to deep (over five metres). Darker or more intense shading means deeper expected flooding. A house in a coloured band sits in a mapped flood-risk area; a house on unshaded ground does not.
To read it honestly, focus on two things: whether the plot is shaded at all, and, if so, which depth band it falls in. A plot at the edge of a shallow band is a very different proposition from one deep inside a three-to-five-metre zone. Remember that this is a modelled design-storm scenario, not a prediction of a specific flood, so treat it as "this is what the official model says could happen here," which is exactly the honest framing we use across our data.
How do I read the landslide layer?
The landslide layer marks sediment-disaster risk areas, typically on and below steep slopes. Japan designates warning areas and, for more severe risk, special-warning areas, and the map shades these. A house on or just below a shaded slope sits in a designated sediment-disaster zone, which is a formal, mapped risk, not a vague one.
The distinction between an ordinary warning area and a special-warning area matters, because the latter reflects a higher assessed risk to buildings and can carry stronger implications for what work is required or permitted. Many affordable rural akiya sit in valleys and on hillsides, so this layer comes up often. A designation is a reason to get specific local professional advice for that plot, not a detail to skim past.
How do I read the tsunami layer?
The tsunami layer shades coastal areas within the modelled tsunami inundation zone, again by expected depth. If a low-lying coastal plot is shaded, it is inside the zone the government models a tsunami could reach; if it is above and outside the shading, it is not. As with flooding, depth bands indicate how severe the modelled inundation is.
The mental model for tsunami risk is "rare but severe." Unlike flooding, which recurs, a tsunami is a low-frequency, high-consequence event, so a coastal house can be lovely and still carry meaningful modelled exposure. The map's job is simply to tell you whether the specific plot is in the modelled reach, which is the fact you want before, not after, you commit to a coastal house. For the wider safety picture, see is it safe to buy an akiya.
What if the map is confusing or the plot sits on a boundary?
Zoom to the exact plot rather than the neighbourhood, check each hazard layer separately, and when a plot sits on the edge of a zone, treat it as inside for planning purposes and get local advice. If you cannot read the Japanese labels, use the colour bands and the layer you have enabled to orient yourself, and confirm anything material with a professional.
Boundary cases are common and genuinely ambiguous, so the honest approach is caution: a plot straddling the edge of a flood or landslide zone deserves the same scrutiny as one clearly inside it. Do not talk yourself into the reassuring reading. The map is a screening tool that tells you where to look harder, and a physical survey and local expertise are what confirm the reality on the ground.
How we know this
Engawa reads these same government hazard layers programmatically and attaches them to each listing, so you get the flood, landslide, and tsunami findings for a specific plot in plain English, with a link back to the source, rather than having to navigate a Japanese portal yourself. We pair these with seismic-hazard data from J-SHIS, the national seismic hazard station. Where a plot falls outside every mapped zone, or where a layer's data is thin, we show an honest null with its source, never an all-clear we cannot support. We map risk; we do not visit sites, so a survey still matters.
Frequently asked questions
Is the hazard portal available in English?
The main national portal is primarily in Japanese, which is a real barrier for foreign buyers. Some municipalities publish English hazard information, and the colour bands are readable without language, but full interpretation often needs translation or help. This is exactly why we surface the findings in plain English per listing.
Does an unshaded plot mean zero risk?
No. It means the plot is outside the mapped zone for that specific modelled scenario, which is reassuring but not a guarantee against every event. Hazard maps model design scenarios, and reality can exceed them. Treat unshaded as lower risk, not no risk, and still get a survey.
What is the difference between a warning area and a special-warning area?
Both are designated sediment-disaster (landslide) zones, but a special-warning area reflects a higher assessed risk to buildings and can carry stronger regulatory implications. A plot in a special-warning area warrants particular caution and specific local professional advice before you buy.
Can I rely on the hazard map alone?
No. The map is a screening tool that tells you which risks a plot faces on paper. Confirming the actual condition of the ground and building requires a site visit and a qualified local professional. Use the map to decide where to look harder, then get expert eyes on the specific property.
The honest bottom line
Japan's hazard maps are excellent and free, and you can read the key flood, landslide, and tsunami risks for a plot yourself once you know the colour bands. Zoom to the exact house, check each layer, treat boundaries as inside, and confirm anything material with a professional survey.
Every listing in our catalogue carries these hazard findings in plain English with source links, so you can skip the Japanese portal; start with Kagoshima or Oita, or ask the team to read a specific plot's risk. Flat fee, no commission.