Tokyo’s disaster-prevention app has added a map of 153 road locations identified as underpass flood-risk points. The Tokyo Metropolitan Government says the app can also display an underpass-flood caution when either of two specified heavy-rain warnings is issued. The update was announced on November 2, 2026. (Tokyo Metropolitan Government announcement)
The distinction between a location marked as risky and a road confirmed to be flooded is essential. The city describes the mapped points as flood-risk locations, not as a live feed of water depth, closures or passability. The feature can help users notice a known kind of risk, but the information provided does not establish the current condition of any particular underpass.
What the update includes
The map covers 153 Tokyo road locations identified as underpass flood-risk points, using the city’s count as of June 15, 2026. The app can show an underpass-flood caution when a Level 4 heavy-rain danger warning or a Level 5 heavy-rain special warning is issued. (Tokyo Metropolitan Government announcement)
Those are two separate pieces of information: a set of locations identified as flood risks, and a caution that can appear when one of the named warnings is issued. The city’s description does not say that the app checks whether an individual underpass has water in it, confirms whether a road is open or predicts flooding at each mapped point. Nor does the announcement say that the feature automatically changes a route.
That boundary matters when interpreting both the map and the caution. A marker identifies a location included in the city’s risk information; it is not a measurement of conditions at the time someone opens the app. Likewise, the warning trigger tells users when the app can show the caution. It does not establish that every mapped location is flooded when the caution appears, or that a location without a displayed caution is safe.
What drivers can reasonably take from it
The most direct use is awareness of whether a journey may pass one of the locations the city has identified. Seeing a point on the map can help a driver recognize that a route includes a mapped underpass flood-risk location. It cannot, on the information available, answer whether that road is passable at that moment.
If the app displays its caution during a Level 4 heavy-rain danger warning or Level 5 heavy-rain special warning, users can understand it as a notice connected to those conditions and to underpass-flood risk. It should not be read as a report that a specific underpass is flooded. The government’s materials do not describe the feature as a real-time assessment of water or road status.
This is also a Tokyo-specific update. The locations in the map are Tokyo road locations, and the announcement does not establish that the same function or map is available elsewhere in Japan. The update should not be treated as a nationwide underpass-warning service.
The city notes that existing users may need to update the app to access the new function. It does not specify a version number in the cited announcement, so users should consult the official app information rather than assume that an older installation already includes the feature. (Tokyo Metropolitan Government announcement; Tokyo Disaster Prevention App update)
The Tokyo app information page lists Japanese, English, simplified Chinese, traditional Chinese, Korean and easy Japanese as supported languages. That list is useful for prospective users, but it does not establish that every screen or notification has identical wording across all six languages. (Tokyo Disaster Prevention App)
A simple way to interpret the map
Imagine checking the app before a drive and noticing that a planned journey passes a marked location. The useful conclusion is that the city identifies that spot as an underpass flood-risk point. If the app later displays its caution during one of the two specified heavy-rain warnings, that is a further notice to take the underpass risk into account. Neither the map marker nor the caution, as described by the city, confirms the road’s current condition. This is an illustration of how to read the feature, not a report of a real trip or app test.
A few common assumptions go beyond what the city has stated:
- “There are 153 underpasses.” The announcement says the app maps 153 road locations identified as underpass flood-risk points. It does not say that these are 153 separate underpasses.
- “The map shows where roads are flooded now.” The mapped points are identified risk locations. The cited information does not describe a live water-level or road-condition feed.
- “A caution means every mapped location is flooded.” The caution can appear when either of the specified warning levels is issued. The description does not say that it confirms flooding at each location.
- “No caution means a location is safe.” The city’s description does not establish that the absence of a caution proves a particular road is passable or free of risk.
- “The feature covers Japan.” The update concerns Tokyo locations. The cited sources do not establish nationwide coverage.
- “All existing users already have it.” The city says existing users may need to update the app to use the new function.
Before relying on the feature
If you use the app, check its official information and make sure you have updated it if needed. Keep the scope of the map in mind: it shows the city’s 153 identified Tokyo road locations as of June 15, 2026, while the caution is associated with a Level 4 heavy-rain danger warning or Level 5 heavy-rain special warning. The available information does not say that the app measures present water levels, reports closures or determines whether a particular road is passable.
The practical value is specific. Tokyo has added information about identified underpass flood-risk locations to its disaster-prevention app and a caution linked to two named warning levels. That can make this type of route risk easier to notice. The feature’s limits are equally important: it is a Tokyo update, its markers are not live condition reports, and the city’s description does not make the app a confirmation of current road safety.
Sources
- New Functions Added to the Tokyo Disaster Prevention App to Prevent Flooding Accidents at Underpasses (2026-11-02)
- Tokyo Disaster Prevention App update (2026-11-02)
- Tokyo Disaster Prevention App (publication date not stated)
