4. Chicago, Illinois, U.S.

Chicago, Illinois, U.S. [huanqiu.com]

Since it was founded in the 1830s on the shore of Lake Michigan, the "Wind City" Chicago has become the center of transportation, industry, finance and entertainment in the Midwest of U.S. Nowadays, more than 9.5 million permanent residents live in the metro area, making it the third third-most-populous city in the U.S. In the coming years, Chicago will suffer from gradual increase in heat waves and flooding.