What did the storms Sandy and Katrina tell us? Aside from strengthening the argument that the climate is changing, they also pointed out the problems that arise from having densely populated areas.
We no longer need large cities. New Orleans and New York City both have one primary reason for existing: they are ports. All the rest that goes on in those two cities could be done anywhere.
There is no need for New York to be a financial center. We do not need to have people in Manhattan skyscrapers. They could do the same work from computers in Iowa or Montana. If we continue to pack humans into cities, we will have more Katrina and Sandy disasters. We will have another World Trade Center catastrophe.
Of course, if global warming goes as many predict, both the aforementioned cities will be underwater in the not-too-distant future. Then their populations really will decrease.