Study: Tokyo is riskiest city. (Property/Casualty: Loss/Risk Management Notes).

When it comes to natural disasters and insured property, Tokyo is the city most at risk, according to a study by Munich Re, one of the world's largest reinsurers.

Munich Re examined 50 of the largest "megacities" in the world and factored in the threat of catastrophes, including earthquakes, windstorms and floods along with the cities' vulnerability, exposed value, and total exposure to the hazards.

The 20 strongest megacities in economic terms account for 27% of the global gross national product, and the insurance industry is more exposed to damage in those cities due to a greater insurance penetration in urban vs. rural areas, the study found. Four of the top 10 riskiest cities are in the United States.

With a population of 34.9 million, Tokyo topped the list, followed by the San Francisco Bay, population 7.3 million; Los Angeles, population 16.8 million; the combined Japanese city of Osaka-Kobe-Kyoto, population 18 million; and Miami, population 4.1 million.

Rounding out the top 10 were New York City, with a population of 21.6 million, and ranked sixth on the list; Hong Kong-Pearl River Delta, population 14 million; Manila-Quezon, population 14.2 million; London, population 12.1 million; and Paris, population 11 million.

Chicago ranked 11th followed by Mexico City; Washington-Baltimore; Beijing; Seoul, Korea; Ruhr area, Germany; Shanghai, China; Amsterdam-Rotterdam, Netherlands; Moscow; and Frankfurt, Germany.