A watery apocalypse for Tokyo?

I didn't even realise, until I saw a special (and fascinating) report on Catalyst last year that parts of Tokyo were at high risk of flooding, and huge engineering projects underground have been built to protect the city.

Well, the recent floods just north of the city have led to some dire warnings about how much worse things will be when the same amount of rainfall hits closer to the metropolis.  It sounds very serious indeed:

With the effects of global warming becoming increasingly obvious, the climatic conditions that triggered torrential rain in Ibaraki and Tochigi prefectures two weeks ago is no longer a rarity, and the odds are “100 percent” that similar downpours will hit Tokyo, says Nobuyuki Tsuchiya, a civil engineering expert and author of the 2014 book “Shuto Suibotsu” (“The Capital Submerged”)....

“It so happened that the rain zone moved (northeast) after striking Tokyo and stayed over the Kinugawa River. But think what a disaster it may have been if the band of rain had moved about 50 km westward and struck the Tone and Arakawa rivers instead....

The rupture of the Tone and Arakawa rivers would cause “far more severe devastation” than that of the Kinugawa deluge, he said.

With the Arakawa, for example, boasting one of the densest populations in its surrounding areas of any river in Japan, extensive flooding would lead to unprecedented fatalities and an economic catastrophe that would send shock waves around the world, Tsuchiya said.

Well, this guy has a book to sell, but it is  not as if he is alone:

Indeed, a 2010 government report released by a panel of outside disaster-prevention experts calculated several possible death tolls in the event that the Tone and Arakawa rivers rupture. The deadliest scenario was if the Tone River broke its banks near the cities of Koga and Bando in western Ibaraki, in which case the death toll could rise to as many as 6,300, the report said.

Tsuchiya said, however, that Tokyo should brace for an even more apocalyptic scenario, noting the amount of rain that entered the Kinugawa River was far larger than that anticipated by the report.

“If Tokyo is struck by the same level of downpours that hit the Kinugawa, I’d say the damage would be far more disastrous.”

It therefore seems that if an earthquake doesn't kill thousands there in the coming years, floods probably will....