We are now used to hearing about once-in-a-1,000-year floods. The fact that we are used to hearing about them tells us that they will no longer be rare. In fact, since climate change is at the heart of these events and continues unabated, we can expect that storms practically everywhere will get worse.
That's because as average atmospheric temperatures continue to rise, the atmosphere will hold more and more water vapor. And, as more and more heat gets stored in the oceans, they will provide more and more energy to the storms which pass over them.
Of course, "once in a 1,000 years" only means that the chances are one in a thousand that such a storm will occur this year or the next. In fact, this phrase doesn't actually reflect weather records. As Vox points out, we don't have reliable records going back that far. We have only about 100 years of such records for the United States, and then not for every locale. Beyond 100 years we are guessing about flood severity based on indirect evidence.
Instead of planning based on such long intervals, we will be faced with a moving target—actually a moving target of probabilities—probabilities which are rising in unknown ways at unknown speeds. Even with all of our instruments, models and scientists we cannot keep up with the changing dynamics of an atmosphere continually perturbed by climate change.