The percentages of citizens vulnerable to 100 and 500 year flooding events are a bit unbelievable to me. While those sound like very long odds the likely of an event during the life of a 30 year mortgage is better than 25% in 100 year locations.
https://www.washingtonpost.com/graphics/2017/national/harvey-flood-compare
Miami, Florida: More than half of residents could be flooded in a 100 year event.
See Attachment