How to Check Flood and Inundation Risk for Rental Properties Using Hazard Maps—A Complete Guide to Selecting Low-Floor Units

Why You Should Check Flood and Inundation Risk for Rental Properties

In recent years, due to climate change, the frequency and scale of flooding and river overflows caused by heavy rainfall and typhoons have increased. There have been past incidents of residential inundation damage in widespread areas including Kanagawa, Nagano, Miyagi, and Fukushima, and awareness of water hazard risks has heightened in rental property selection.

When selecting a rental property, many tenants focus on "distance from the station," "layout," and "rent" while overlooking flood and inundation risk. However, when flooding occurs, substantial costs arise from property damage, prolonged evacuation, and moving expenses.

Verification of flood risk in rental properties is mandatory: Since 2020, disclosure of "the location of the target property on water hazard maps" in important transaction document explanations for real estate transactions has been required. Before signing a lease, you can receive an explanation of flood risk from a certified real estate agent.

Types of Hazard Maps and How to Check Them

Flood Hazard Maps

These maps display the estimated depth of inundation caused by river overflow or internal water flooding (poor rainwater drainage).

How to Check:

1. Access the Ministry of Land, Infrastructure, Transport and Tourism's "Hazard Map Portal" (https://disaportal.gsi.go.jp/)
2. Select "Overlaying Hazard Maps"
3. Enter the property address to check inundation estimates

How to read the inundation depth color coding: | Inundation Depth (Maximum Expected Scale) | Color | Risk | |---|---|---| | Less than 0.5m | Light yellow | Below-floor flooding possible | | 0.5–1.0m | Yellow | Floor-level flooding (1st floor requires caution) | | 1.0–3.0m | Orange | 1st floor fully submerged; 2nd floor reaches floor level | | 3.0–5.0m | Red | 2nd floor or higher necessary | | Over 5m | Dark red | High-rise floors required for safety |

Landslide Hazard Maps

For properties near mountains or hills, you should also verify the risk of landslides and steep slope failures.

How to Check: Use the same portal site and select the "Landslide Hazard" layer

• •Landslide Alert Zone (Yellow Zone): Areas where landslide disaster risk exists
• •Landslide Special Alert Zone (Red Zone): Areas where substantial damage is likely to occur

Tsunami Hazard Maps

For properties near coasts or ports, and in low-elevation coastal areas, verify tsunami risk.

How to Check: Consult the "Tsunami Hazard Map" published by your municipality or access it through the same portal site.

Assessing Flood Risk When Selecting Low-Floor (1st and 2nd Floor) Properties

1st Floor Properties: Risks and Decision Criteria

The 1st floor has the highest flood and inundation risk. When inundation occurs, property and furnishings can be submerged by below-floor and floor-level flooding.

Conditions Where 1st Floor Properties May Be Acceptable:

• •Inundation estimate is "less than 0.5m" (only below-floor flooding anticipated)
• •The area is sufficiently distant from rivers and has high drainage capacity
• •The apartment is on the 1st floor with the property grounds higher than street level
• •The property grounds are elevated (higher than surrounding elevation)

Conditions to Avoid for 1st Floor Properties:

• •Inundation estimate is "over 1.0m"
• •Adjacent to or near rivers or irrigation channels
• •Area with history of inundation
• •Terrain is lower than surroundings, forming a "bowl-shaped" depression

2nd Floor Properties: Risks and Decision Criteria

The 2nd floor has significantly lower risk than the 1st floor, but in areas with inundation estimates exceeding 3m, floor-level flooding may still occur on the 2nd floor.

Conditions Where 2nd Floor Properties Are Safe:

• •Inundation estimate is "2.0m or less"
• •The area on the water hazard map is yellow (0.5–1.0m) or lower

For 3rd Floor and Above

In areas with inundation estimates under 5m, the 3rd floor and above have virtually no flood risk. However, landslide risk should be verified separately.

Key Points to Verify During Property Viewings

Check the Surrounding Terrain

• •Is the property in a depression? Land lower than surrounding areas collects rainwater easily, increasing inundation risk
• •Are there rivers or irrigation channels nearby? Areas within 500m of rivers require flood risk verification
• •Are there underground parking or basements? These become hazardous during flooding

Check the Building Exterior

• •Water line marks on the building exterior: Buildings that have experienced flooding may have marks (stains or discoloration) on walls indicating past water levels
• •Presence of flood barriers at entrance: If flood barriers are installed, they may have been added as past inundation protection (confirm with management company)
• •Position of ventilation outlets: Buildings with low-positioned ventilation outlets risk damage to ventilation systems during flooding

Questions to Ask the Management Company

• •"Has this property or the surrounding area experienced flooding or inundation damage in the past?"
• •"Will the Important Transaction Document include information about flood hazard maps?" (mandatory since 2020)

The Relationship Between Flood Risk and Rent

Properties in high-flood-risk areas (areas with high inundation estimates) tend to have lower rents than surrounding market rates.

How to Consider This:

• •Lower rent comes with trade-offs in risk
• •High-flood-risk areas come not just with cheaper rent, but also with the risk of property and lifestyle damage in a disaster
• •Flood insurance (water damage coverage under fire insurance) premiums also tend to be higher

The Importance of Fire Insurance (Water Damage Coverage)

Tenant fire insurance can cover property damage from flooding and inundation by adding "water damage coverage."

Verification Points:

• •Check if the management company's designated fire insurance includes "water damage coverage"
• •If not included, consider choosing fire insurance with water damage coverage
• •Water damage coverage is especially important in high-inundation-estimate areas

Summary: Flood Risk Checklist for Rental Property Selection

• •[ ] I verified the property's inundation estimate using the Hazard Map Portal
• •[ ] I carefully evaluated 1st and 2nd floor properties in areas with inundation estimates exceeding 1.0m
• •[ ] I checked the terrain to confirm no nearby rivers, irrigation channels, or low-lying areas
• •[ ] I verified the building exterior has no signs of past inundation
• •[ ] I confirmed with the management company about any history of inundation
• •[ ] I reviewed flood hazard map information in the Important Transaction Document
• •[ ] I confirmed the fire insurance includes water damage coverage

Gas leaks and carbon monoxide poisoning pose a life-threatening risk that can develop without your awareness. This expert guide covers practical safety measures renters should know: how to check alarm systems, the proper steps to take when you discover a gas leak, and how to safely use heating equipment in winter.