It's just a matter of time before Tokyo is struck by the same magnitude of flooding that devastated parts of the northern Kanto region this month, and should the capital remain unprepared it will most likely be "annihilated," followed by an unprecedented death toll and economic damage, experts warn.

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").

The downpours that led to the Kinugawa River overflowing its banks in Ibaraki were mainly caused by a concentration of thunderclouds that formed a lengthy band of rain, a phenomenon that was also responsible for torrential rain that killed 74 people in the city of Hiroshima in summer 2014.