Scientists say super typhoons are likely to occur with greater frequency as the planet warms. And they can cause devastating damage. In 2013, a 9-meter high storm surge hit the coastal areas of the Philippines, leaving over 7,300 people dead or missing.
The Tokyo government released data based on the highest estimated storm surge in Tokyo Bay caused by a major storm with atmospheric pressure of 910 hectopascals. It found that 17 out of the city's 23 wards could be flooded, including the central business districts.
The estimate is based on a super typhoon making landfall in the Kanto region, which includes Tokyo, causing a storm surge of nearly 6 meters to flow through rivers from the sea. Water could be 10 meters deep in the most severely-hit areas.
Central Tokyo would be inundated. Shinbashi is one of the most heavily used stations in the city and the area would be flooded by a meter of water in this scenario. Business and commercial districts such as Marunouchi and parts of Ginza would also be submerged.
The government says it is unlikely the water would recede overnight. Areas that are mainly zero elevation could remain under at least 50 centimeters of water for over a week. If flooding continues for that long, around a million residents would have to be evacuated.
Local governments have started considering how to evacuate residents but are yet to come up with specific plans.
Residents are afraid of the possible dangers. One says she's worried about how quickly she can escape with a small child. Another says she isn't sure how far she can run by herself.
Expert: People need to change the way they think of evacuation planning.
Professor Taro Arikawa of Chuo University says a super typhoon would necessitate unprecedented measures. He is an expert in tsunami and storm surge disaster management.
Arikawa says the probability of the maximum estimated storm surge hitting Tokyo Bay is extremely low, but that it is important to prepare for a disaster of that level--or worse.
Last September, more than 6.5 million people were forced to evacuate in the US state of Florida by Hurricane Irma.
Arikawa conducted an on-site survey of the storm's aftermath. He says many of the evacuees were forced to travel long distances. In Japan, he says the equivalent would be evacuating to surrounding prefectures.
Arikawa says a storm surge presents different challenges for evacuation than other disasters. For example, people flee basically on foot during a tsunami.
For a storm surge, he says it is important to evacuate beforehand because of accompanying flooding, heavy rain, and severe winds. He says plans to evacuate residents by car or public transportation one or several days in advance are needed.
The government estimates say many ward offices, core hospitals, and business districts would be flooded. Arikawa says cooperation between hospitals must be in place, so patients can be evacuated.
Arikawa stresses that disaster-preparedness plans must be formulated though cooperation not only among wards, but with the metropolitan and central governments as well.