“Japan Weighed Evacuating Tokyo in Nuclear Crisis”, NYT/The Age, 27/2. This article describes the Japanese government’s then-secret plans to evacuate Tokyo after the earthquake and tsunami if the damaged Fukushima Daiichi reactor plant went into meltdown:
Mr. Kan and other officials began discussing a worst-case outcome if workers at the Fukushima Daiichi plant were evacuated. This would have allowed the plant to spiral out of control, releasing even larger amounts of radioactive material into the atmosphere that would in turn force the evacuation of other nearby nuclear plants, causing further meltdowns. The report quotes the chief cabinet secretary at the time, Yukio Edano, as having warned that such a “demonic chain reaction” of plant meltdowns could result in the evacuation of Tokyo, 150 miles to the south.
Not described in the article is how the government would undertake the immense task of evacuating a huge city of 13 million (though looking at the Wikipedia page, the greater Tokyo region is an astounding 35 million). Japan is pressed for space on its islands as it is (despite gloomy alarmist reports about a declining birth rate). Perhaps other countries might take some of the evacuees, assuming they wanted to go, but nearby China is overcrowded already, and places such as Australia are mostly desert and the infrastructure in the cities are not coping with the current population. So disasters like these demonstrate that a large and growing population rapidly becomes a liability in such times.