The basic problem is this. We really don't have regional flood control policies. So, what did not flood yesterday may well flood tomorrow due to all the development west or north of your home in an adjoining area or county.
As the former rice fields and relatively low lying areas are paved over, and the bayous/creeks straightened and concreted, the water does not soak in, and instead, rushes down stream flooding previously developed areas.
Much more to it than that, but thats the basic overview.
My place in NW Houston was built in the mid-80's. No flood insurance even required. Well above the 100 year flood plain. And, there was little development upstream in my water shed. Since then, the flood waters get closer and closer and closer with each flood event. As the water shed is developed.
Last three events, flood waters were forced "up stream" in our local drainage ditch because the local major creek could not handle the volume of water. This inundated homes just a couple blocks from me. Homes that had never seen water since their construction in the late 70's/early 80's.
Same basic story in many parts of the Houston area. There are even parts of Houston in which 40, 50, or 60 year old homes are now being lifted onto 6 foot high foundations to avoid future flood events. Newly constructed homes built on 6 foot raised pads.
So, big picture, unless its a newly constructed home on a raised foundation, probably should expect it might have future flood issues on the SW side of the Houston metro area.