The Terror of a Linear Rain Band Beneath Tokyo! Doors Won’t Open, Water 30 cm Deep Makes Walking Difficult… “Signs” to Help You Escape in Time

Plunged into Darkness by a Power Outage… The Terror of Basement Flooding

This year, the Japanese archipelago has been ravaged by the “water demon”—just as the heavy rains that struck Chiba Prefecture on August 13 seemed to have subsided, a linear precipitation zone formed in the Hokuriku region, flooding many homes. Since then, Aomori and Kyushu have also been hit by heavy rains one after another. No matter where you are in Japan, you can no longer feel safe.In fact, on August 22, a “Level 4 Heavy Rain Danger Warning” was issued for the Tokyo area, and a “Level 4 Flood Danger Warning” was issued for the Zenpukuji River. On that day, rainfall exceeding 120 mm per hour was recorded near Itabashi Ward.In August 2024, the area was also hit by torrential rain of about 100 mm per hour, causing flooding at four stations, including Ichigaya Station and Azabu-Juban Station.

“In underground areas, it’s too late to try to escape once the water starts coming in. It’s important to pay attention to announcements from the facility and notice any unusual changes in the surrounding area early on, and move to a safe place before the water arrives,”

said Koji Matsumoto, who is both a certified meteorologist and a certified disaster prevention specialist.

“Stairwells become pathways for water, causing it to pour into underground areas. If flooding affects electrical equipment, it could lead not only to power outages but also disrupt multiple functions, such as lighting, elevators, communications, and drainage” (Koji Matsumoto; same below).

Is there no way to prevent water from flowing in? What about flood barriers or watertight doors?

“I don’t know if they are installed at every entrance and exit. Even if they were installed, sealing off every entrance and exit with water barriers or watertight doors would block evacuation routes.”

As the water level rises, water pressure can make doors difficult to open, potentially rendering evacuation routes unusable.According to documents from the Ministry of Land, Infrastructure, Transport and Tourism, a water depth of 30 cm is cited as a key benchmark for evacuation in underground spaces, indicating the risk that walking becomes difficult or that water pressure makes it hard to open doors. In areas where water rushes down staircases, walking reportedly becomes difficult at a water depth of 30 cm.

Even if you are lucky enough to reach an emergency exit and think, “If I open this door, I can get out!” you may find yourself unable to open it and helpless in the face of the rising water level.

In 2021, during a series of record-breaking torrential rains in Zhengzhou, Henan Province, in central China, subway stations and tunnels were flooded, trapping hundreds of people inside trains.The train cars were plunged into darkness, and oxygen levels dropped inside the trapped cars. One woman interviewed by Reuters said, “The scariest thing wasn’t the water—it was running out of air.”

Announcements inaudible due to the sound of rushing water

In fact, the cases of underground flooding in Tokyo are not limited to the four stations—including Ichigaya Station—affected in ’24.In 1981, torrential rain with a peak hourly rate of 75 mm caused urban flooding, resulting in approximately 30 cm of water accumulation in the Shinjuku Subnade; in 1999, torrential rain with a peak hourly rate of 99 mm caused approximately 20 cm of flooding in the Shibuya underground shopping arcade and the area surrounding the station.

“Tokyo has experienced repeated instances of flooding in underground spaces in the past.”

The area beneath the Shinjuku Grand Underpass has a bowl-shaped topography, and the road surface in this section is about 1.5 to 2 meters lower than the surrounding area. The area near the center of Kabukicho is also one of the deepest points. The area around Shibuya Station also lies at the bottom of a bowl-shaped topography.

Given this topography, the Tokyo Metropolitan Government has established Flood Prevention Councils for underground shopping centers and other facilities in 12 districts—including Shinjuku West, Shinjuku East, and Shibuya—and is working with relevant businesses to implement flood prevention measures.

“If evacuation or evacuation instructions are issued by the facility, it is important to follow those instructions.”

Of course, as a general rule, following the facility’s instructions is paramount; however, you should also prepare for the worst-case scenario—such as during a panic or a power outage caused by flooding—when “announcements cannot be heard or are not functioning.” In real-life situations, the sound of rushing water could drown out announcements. This is even more likely if you are wearing headphones.

Furthermore, during events like the Chiba torrential rains, some people reported that “the water rose in the blink of an eye.” If you wait for an announcement, there’s a real possibility you won’t be able to escape.

Both Shinjuku Station and Shibuya Station are currently undergoing redevelopment and have turned into mazes. In an underground mall where it’s easy to get lost even under normal conditions, what should you do if you’re caught in a flood in the pitch dark?

As mentioned earlier, when water is rushing down the stairs, it becomes difficult to walk even in water just 30 cm deep.

You can’t see your feet. You don’t know which way to go. If you fall after being pushed by a panicked crowd in such an extreme situation, there is a real possibility you could drown.

“The worst thing you can do is panic. If flooding has begun, do not try to force your way against the incoming current. Instead, follow the facility’s announcements and the instructions of staff to move to a safe, non-flooded route or location. Some people film water cascading down the stairs like a waterfall and post it on social media, but such behavior is tantamount to throwing your life away.”

Use “Train Service Suspended” as a Signal to Evacuate

The key to underground disaster preparedness is to evacuate before the water arrives, not after it has already entered.

If heavy rain is forecast, check updates frequently. Before danger strikes, follow the facility’s instructions and move to a safe location. And there’s one more thing you should pay close attention to:

“train service status. During the heavy rains of ’24, the Tokaido Shinkansen stopped running between Tokyo and Shin-Yokohama at 6:38 p.m., and by 6:50 p.m., the entire Yamanote Line had also stopped. It was during this time that road flooding and subway station inundation occurred.”

The “Record-Breaking Short-Duration Heavy Rain” advisory was issued shortly after that, at 7:07 p.m. While a suspension of rail service isn’t in itself an evacuation advisory, since the service status is displayed on electronic boards, it’s a good idea to check those as well.

“No one knows what an unexpected torrential downpour will be like or what will happen underground at that moment. Since conditions can change rapidly during localized torrential rain, waiting until danger is right in front of you to take action may be too late.”  

When heavy rain is forecast, avoid going out if possible. If you do go out, check the weather conditions frequently. Carry a whistle and a small flashlight with you just in case. These self-help measures are crucial.”