Underground tunnels reduce flood damage in the Japanese capital by 90%.
The underground tank system helps Tokyo cope with floods.
Cecilia Tortajada still remembers the time she walked down the deep stairs to visit one of Japan’s engineering masterpieces, a giant water tank that is part of the `defense system` that helps Tokyo fight floods.
`You feel very small,` said Tortajada, a water management expert at the Water Policy Institute at the Lee Kuan Yew School of Public Policy, Singapore.
The `anti-flooding temple` is located at a depth of 22 meters underground, its full name is the Urban Area Underground Outlet Canal (MAOUDC).
Over the past seven decades, the Japanese capital has perfected the art of dealing with floods and calls its complex flood defense system a world wonder.
Tokyo has a long tradition of fighting floods, because the city is located on a plain surrounded by five river systems and dozens of large and small rivers that continuously swell each season.
`I don’t know who decided to put Tokyo here,` Tortajada said half-jokingly.
Although Japan has spent centuries fighting floods, the current flood protection system in Tokyo only really took shape after the war.
Faced with the severe consequences of storms and floods, the Japanese government is determined to take action.
Tokyo planning experts have to deal with many different types of floods.
After decades of planning for these scenarios and building corresponding structures, Tokyo now boasts a flood defense system with dozens of dams, reservoirs and levees.
Huge tank underneath Japan’s capital Tokyo.
MAOUDC, worth $2 billion, and its `floodproof temple` are among the most impressive engineering feats Tokyo possesses.
This system draws water from small and medium-sized rivers in the northern area of Tokyo and circulates them to the larger Edo River.
Each of these underground tanks is large enough to hold a space shuttle or the Statue of Liberty, and they are connected through a tunnel system.
`It’s like a facility out of a science fiction story,` said JCA’s Inaoka.
However, Inaoka admitted that changing rain patterns due to climate change will challenge Tokyo’s infrastructure, making planning for floods very difficult.
Based on historical rainfall data, the city government designed Tokyo’s defenses to withstand up to 50 mm of rain per hour, especially in places where people and property gather.
According to the Japan Meteorological Agency, in many areas of the world, the number of days of heavy rain has increased over the past 30 years, a sign that rainfall patterns are changing.
A walkway inside the rainwater tunnel system in Tokyo.
The Tokyo Metropolitan Department of Construction confirmed it is aware of the changes taking place and has raised its criteria for assessing rainfall in response to flooding.
In a book published in 2014, Tsuchiya, director of the Japan River Research Center, warned that Tokyo is not ready to deal with heavy rains caused by global warming.
In early 2018, heavy rains in western Japan caused hundreds of deaths and millions of dollars in economic losses when many rivers burst their banks, causing serious flooding.
In Singapore, Cecilia Tortajada and a series of other experts are trying to find ways to protect this island nation against future sea level rise.
`If a well-prepared country like Japan is still affected, if a city like Tokyo is still flooded, we should all be vigilant,` Tortajada emphasized.
The operating room of the Tokyo North area flood discharge system.
