Tokyo won't be able to cope with Katrina-like flooding
When Hurricane Katrina devastated New Orleans and much of the U.S. Gulf Coast in 2005, there were a lot of nervous government officials in Japan, wondering what would happen if Tokyo were ever hit by a typhoon of similar magnitude to Katrina. It seems that every time there is a torrential downpour or a few snowflakes in Tokyo, the transport system is thrown into chaos, schools close and TV networks start posting bulletins. So what would happen to Tokyo and the rest of the Kanto region in the event of a major flood and what countermeasures are in place to enable a quick response from the government?
According to the Cabinet Office which oversees the various ministries and bodies in charge of disaster management in Japan, one half of the entire country’s population is concentrated in low-lying inundation areas and the basins of 248 major rivers are designated as potential flood hazards. In the Tokyo metropolitan region, those rivers include the Sumida, Tama, Tone, Arakawa, Kanda, Ayase, Naka and Daiba rivers. Most of these waterways are relatively steep with a short distance from the source to the sea, resulting in rapid flow.
In the Tokyo area, an estimated 116 square kilometers of land lies below sea level, which means they would be inundated should embankments collapse. Nerima Ward is the highest ward, while large parts of Kita, Arakawa, Edogawa, Koto, Adachi, Taito and Katsuhika wards would be at most risk during a major flood, the Cabinet Office says.
However, if you live in those wards, don’t move out and head for Nerima just yet. The good news is that Japan has never had a typhoon as strong as Hurricane Katrina in its recorded history. The most destructive typhoon was Typhoon Kathleen in 1947, which claimed 3,769 lives. Nevertheless, smaller floods and sediment-related disasters have occurred in more than 90 percent of municipalities throughout Japan in the past ten years. A deluge in Tokyo in October, 2004, for example, flooded Azabu-juban subway station. Last September, Typhoon No. 9 hit the Kanto region, stopping JR lines and stranding 1.2 million commuters. The Tama River reached a dangerous level and some residents had to be evacuated from near its banks.
“Experts in the U.S. and Japan have said that a disaster like Katrina only happens once every 400 years,” said Goro Yasuda, counselor for disaster management at the Cabinet Office, which reports directly to the prime minister. “Sadly, in the past, the mindset has been to prepare for disasters based on recent events, rather than on the worst-case scenario. However, we can no longer take anything for granted. The Ministry of Land, Infrastructure and Transport has been shoring up embankments and simulating the flow of water in the event of a major flood through computer analysis. There’s no doubt that if we had a Katrina, or even another Typhoon Kathleen, there would be massive damage. It’s not just typhoons, either. We have to predict what would happen if an earthquake caused an embankment to break.”
Officials visited New Orleans after Katrina
Yasuda was one of many officials who visited New Orleans in the aftermath of Katrina to meet officials of FEMA (Federal Emergency Management Agency). “FEMA came in for a lot of criticism for its response to Katrina. But I think their evacuation programs were basically quite good. In Japan, we do not yet have such evacuation programs in place,” he admitted.
Many studies have been conducted by the River Bureau, the Central Disaster Management Council and universities over the past year to estimate what would happen in a worst-case scenario. The Research Center for Disaster Reduction Systems at Kyoto University released a report last summer on what might happen to the rivers in Tokyo in the event of a major typhoon. “The Arakawa and Sumida rivers are close to each other in many areas. If a levee along the Arakawa river breaks, then the water would flow toward Sumida and reach Ginza within 20 hours. It is possible that Ginza would be under two meters of water, Kasumigaseki below knee level, and Marunouchi under about 30 cm of water,” the report warned.
Since many buildings in the metropolitan area have their own electricity generators underground, once the water penetrates underground, none of those facilities would function at all. Subways would also be affected, the Kyoto University report said. “If the levee near Kitasenju station in Adachi Ward breaks, then the water would flow into the station on the Chiyoda line. It would only take about 2 to 3 hours before the water reaches Otemachi following the subway path.” Making matters worse, the report warned that Tokyo’s sewage system would be overwhelmed, causing disease outbreaks, roads would be flooded, while cars, trees, manholes and other debris would float in various parts of the city.
6,000 deaths in Tokyo predicted in event of major flood
Meanwhile, in another scenario released last October, the Central Disaster Management Council, which is overseen by the Cabinet Office, predicted that 6,000 people would die, more than 2.32 million others would be displaced and 694,000 households would be waterlogged due to massive flooding if levees along the Tonegawa broke. Economic damage was estimated at 34 trillion yen. The CDMC studied 25 flood scenarios (by computer) caused by embankment collapses in different spots along the Arakawa river and high tides in Tokyo Bay.
Takayuki Kishii, a professor at Nihon University and a member of the CDMC research panel, said that most projections to date have been based on what has happened in recent times rather than taking into account that once-in-500-years scenario. He said that Japan could learn from the Netherlands as well as the flood control efforts along Britain’s Thames River, both of which have been designed to cope with a calamity of gigantic proportions. One trend, he pointed out, is that in recent years, some parts of the world have been swamped by downpours far beyond what had been anticipated. “Drainage systems in Japan were constructed on the assumption that strong rainfall in a relatively short period happens rarely. But recently, we’ve seen torrential rain in urban areas more often, sometimes heavily concentrated rainfalls of up to 100 mm.”
According to the Japan Meteorological Agency, the average seawater temperature rose by 0.5 degrees Celsius, but in the Sea of Japan, it has risen about 0.7 degrees to 1.6 Celsius in the past 100 years, which is believed to be the cause of bigger typhoons that the Kanto region has been experiencing. Another trend with recent typhoons is that more of them are reaching the mainland, the agency said.
While the government has measures for dealing with the aftermath of more frequent disasters such as earthquakes, it lags a little on floods. In the event of massive flooding, there would be a host of problems, such as rescuing people from isolated areas or tops of buildings, building shelters, restoring power, telecommunications and transport networks, dealing with flooded underground arcades and coping with epidemics and a shortage of drinking water.
Subway operator, Tokyo Metro Co Ltd, is confident it would be able to handle things in the event of major flooding. “We have implemented many measures against flooding based on past experience,” said Koji Yamaguchi, a spokesman for the Safety Affairs department of Tokyo Metro. “Stop-flood boards and flood prevention doors have been installed at station entrances. Some entrances were raised at locations where the ground is low. Flood protection devices are installed at ventilation hatches. For areas where the tunnel entrance is prone to flooding, flood walls and flood prevention gates have been installed.”
Furthermore, he said, all Tokyo Metro staff are trained to handle such natural calamities and drills are carried out on a regular basis. “Each station has a unique manual with pictures and detailed diagrams of where equipment is located and details of past experiences and how they were handled.”
Overall, the biggest challenge in a disaster is coordination of response efforts, said Yasuda of the Cabinet Office. “The fire departments in each area are in charge of rescue and recovery. Local governments have their own flood defense teams. They conduct drills once a year or more often. Self-Defense Forces are also involved in their drills. In the past, there were a lot of people who disliked the involvement of the SDF because of their anti-war feelings, and these people wouldn’t even take part in drills, but now their involvement has become more accepted. Many local governments have also created hazard maps in order to tell local residents about the danger of floods, such as depth of water projected – in other words, if their house will end up under water. However, the Ministry of Land, Infrastructure, Transport and Tourism has to take charge much more efficiently than it has done.”
Embankments not in good condition
One factor, which remains alarming, is the state of embankments and levees along Japan’s rivers. Earthquake prevention gets far more budgetary resources than flood risk countermeasures. “Some embankments were built back in the Edo period (1603-1867). We are gradually reinforcing them to make them higher, but it’s not so easy,” said Yasuda. “For example, if there are already buildings near a river, we cannot construct new embankments. So we have a joint project with developers when these buildings are rebuilt, creating new space for so-called ‘super embankments’ with gradual slopes.”
Experts say the Arakawa River needs urgent attention—according to a survey that the ministry conducted last year, as much as 58% of the levees along that river aren’t up to the necessary safety level. On the positive side, huge underground discharging channels have been completed at various points beneath the Edo and Tone rivers. As for Tokyo Bay, Kishii of Nihon University said embankments next to the sea and embankments between canals and land are being constructed. “They’re not complete yet and I’d have to say construction is not going smoothly.”
To boost its readiness, the government monitors rainfall and water level in rivers by utilizing a wireless telemeter system and water immersion sensors that automatically transmit data from remote locations. From this month, the government also started measuring rainfall accumulation in soil as a means of predicting landslides. The Flood Control Act, amended two years ago, requires municipal governments to make sure residents are familiar with hazard maps, disseminate disaster information and quickly implement evacuation procedures.
Which is easier said than done. “One of the biggest problems we face now, though, is apathy among the Japanese population,” said Yasuda. “After Katrina, 80% of flood victims in New Orleans were evacuated. When we surveyed people in low-lying areas of Japan, only 46% said they would evacuate. Many people, especially aged under 50, live in urban areas and have never experienced large scale disasters at all. They are not concerned about flooding. I am afraid it will be very difficult to make sure everyone can evacuate in emergencies. If only 46% are prepared to go in advance of a flood, then several thousands of people are going to die or be cut off. And if they are elderly or children, then their chances are not good.
“When the Central Disaster Management Council released its report last October, that was the first time it had ever forecast the number of deaths from floods instead of just saying that damages would be in the trillions of yen, as it normally does. We wanted to jolt people’s attention. You should never underestimate the power of floodwaters. The damage is not just monetary.”