Giant storm surge could submerge a third of Tokyo: study


About a third of central Tokyo could be left under water and nearly 4 million people flooded if a supertyphoon strikes the capital and causes storm surges, a new study warns.

The Tokyo Metropolitan Government unveiled its first estimate of the capital’s vulnerability to damage from typhoon-related tidal waves Friday as the risks from storm damage continue to increase globally.

According to the report, 212 sq. km (85 sq. miles), or one-third of the central Tokyo, could be inundated by as much as 10 meters (33 feet) of water if a supertyphoon creates high tidal waves in the Kameido district of Koto Ward.

The report assumes a typhoon as powerful as one that left more than 3,000 Japanese dead or missing in 1934, or one with an atmospheric pressure of 910 hectopascals at its center and moving at 73 kph, causes storm surges and river flooding from heavy rain and burst dikes.

An event this severe could affect as many as 3.95 million people in the city, flooding the business and entertainment districts as well as major rail stations, the study said.

Tokyo has a population of 13.7 million.

The report also estimates that 13.61 sq. km, or 99 percent, of Sumida Ward, 34.15 sq. km, or 98 percent, of Katsushika Ward, and 45.46 sq. km, or 91 percent, of Edogawa Ward will be flooded in such an event.

The amount of area that will be submerged in water more than 50 cm deep for more than a week is expected to total some 84 sq. km, affecting 1.36 million people during the daytime and 1.37 million people at night, in accordance with the tides, the report said.

In particular, Tokyo’s eastern zone near the Arakawa River would be flooded for more than a week if rising tidal waves at Tokyo port break through the river’s levees.

Based on the estimate, the Tokyo Metropolitan Government said it plans to update evacuation measures and review how it disseminates warning messages to its residents.

Earlier on Friday, Fukuoka Prefecture unveiled a similar estimate, saying a tidal wave as high as 7.3 meters is likely to inundate Higashi Ward in the city of Fukuoka if a supertyphoon approaches.

Of the 16 municipalities in northern Fukuoka Prefecture, it is possible that eight could be hit by a tidal wave 5 meters or higher.

The Higashi Ward Office will likely be flooded by 4.4 meters of water, while Fukuoka City Hall will likely be flooded by 3.3 meters, suggesting that municipal offices — which serve as the headquarters for natural disasters — are likely to be knocked out.

Places estimated to be inundated to a depth of 50 cm or more are likely to see water subside within 24 hours, the prefecture said.

“But we need to prepare for an evacuation that may last for a long period of time,” an official the at Fukuoka Prefectural Government office said.

Big storms sometimes trigger landslides and floods that often lead to sizable casualties.