Tokyo, the world’s most populated metropolis, is building defenses for a once-in-200-year flood that could dwarf the damage superstorm Sandy wrought on the U.S. East Coast.
Japan’s capital, flanked by rivers to the east and west, as well as running through it, faces 33 trillion yen ($322 billion) in damages should the banks break on the Arakawa River that bisects Tokyo, according to That’s more than five times the $60.2 billion aid package for Sandy that slammed into the U.S. northeast last October.
“Japan hasn’t prepared enough,” said Toru Sueoka, president of the an organization of engineers, consultants and researchers. “Weather patterns have changed and we are getting unusual conditions. We need upgrades or else our cities won’t be able to cope with floods.”
In 2008, for the first time in human history, half of the world’s population lived in urban ard Flooding. The report says that trend combined wit means the world’s cities will bear the biggest loss of life and the largest economic costs from flooding.
Should the Arakawa River break its banks, about 2,000 people in Tokyo may lose their lives and around 860,000 will be stranded, according to the government. The waters would flood subway and regular train lines, crippling 97 stations.

Flood Defenses

The capital’s Edogawa City, one of Tokyo’s largest wards that is sandwiched by two major rivers, predicts it will cost 1.7 trillion yen to strengthen and rebuild the banks of the Arakawa and Edogawa rivers to prevent breaching during a flood, said Naomasa Tachihara, director of Edogawa’s department of public works planning.
Floods are the world’s most frequent destructive natural event and the costs of economic damage have surged, according to the 2012 World Bank report, citing examples in Pakistan, Australia, the Mississippi in the U.S., and Bangkok in Thailand in 2010 and 2011.
London’s effort to prevent flooding is a barrier spanning the River Thames completed in 1982; a three-decade project started after a flood in 1953 that killed 300 people.
The Thames barrier across a 520-meter stretch of the river was closed four times in the 1980s, 35 times in the 1990s and more than 80 times since, according to the Environment Agency.