Tokyo's population skyrocketed from 1.5 million people in 1900 to 28 million people today. The sprawling city sits on a fault line that seismologists warn could rupture at any time. But most of the world's biggest cities are in countries far poorer than Japan, places where people already are living in wretched conditions. The poor generally live in unstable homes and are forced to crowd into hazardous areas. When a natural or man-made disaster hits, the death toll can be astronomical.
Thousands lose their homes and meager belongings, and the poor descend deeper into poverty.
Overpopulated cities are becoming bigger targets for natural disasters. By the third decade of the 21st Century global climate change will become increasingly obvious and ominous. In China, people will begin to notice that the winters have grown warmer. Increased rainfall will deliver even more flooding in coastal provinces and inland droughts will lead to more famines, according to the Global Scenario Group, an international consortium addressing long-range environmental and development possibilities. It's a grim outlook for the country that lost more lives to natural disasters than any other nation during the 20th Century.