Question is, why humans never learned to not build housing on flood plains? Not just Tokyo, but all over the world people are being idiots and decide to live where they shouldn't,(reply>), @Yayatsuma not on the floodplain but off to the side? Just saying if people live where nature does stuff, don't come crying when nature do it's thing,(reply>), Being that close to the biggest city in Japan &gt;&gt;&gt;&gt;&gt; the risks of flooding. <br>People have always used floodplains for farming and so on, it's fertile land, flat and easy enough to build on and being close to a river was traditionallly a huge advantage for defence, transport, fishing etc. <br>It's a little narrow minded to call people idiots for building there, where would you have them live instead? The desert? On a mountain slope?