Because all the soil is gone and cement does not absorb water drainage systems can get full heavy torrential downpours upriver rain are all the major reasons cities can flood
Winter Garden doesn't flood
Recent flood has affected Sindh badly. Almost all major cities of Sindh have been hit by flood. Thattha, Badin and Nawabshah are the cities which have been almost destroyed.
flood houses and cities
I believe one of the cities involved was named Greenfield...
Montana
There are no cities in Antarctica. As well, there are no floods: it's too cold.
The entire earth was covered in the flood of Noah's day, so all cities at the time were flooded.
flood defense systems
Many archeologists claim walled cities post flood were to keep out post-flood animals (hostile, high fecundity, low gestation period, large littered, hostile (unlike the non-aggressive animals pre-flood wherein pre-flood man and animals had been at peace with one another as there was no meat eating).
The migration of thousands of farmers to industrial cities.
We construct dams to make sure water doesn't flood states and cities.
Early man migrated to follow the herds for food. Today it may happen because coast cities are starting to flood due to the melting ice cap. There are many of the world's cities starting to flood. You can find pictures of them online.