I just read that one of the side effects of hurricane Sandy was that the rats and mice that were in the subway tunnels, basements and parking garages had to come to the surface to escape the flooding.
Now they will be looking for two things, food and shelter. The unlucky buildings that give them both will have new residents. There is a great introduction here about why they are such a problem and what to do about it. Here is a more comprehensive discussion. Most of this I knew, but this article claims they can consistently survive a fall of 50'. Since they are now above ground, and they are good climbers, hmmmmm, I have an idea for an Indie horror film.