I guess what I meant wasn't "non-independent events". However, there is still a fundamental difference. The probability of a 500-year flood happening next year is still 0.2%. With a birthday paradox, the filling of birthdays is what causes the explosion in probability. Assuming no collisions so far, the 20th person you add to the room has a 19/365 chance of colliding, while the 2nd person only has a 1/365 chance.

I'm not sure how to succinctly phrase this idea. Maybe "non-constant probabilities"?

In the terms of an example:

If you put 400 people in a room, the odds that no two of them share a birthday have gone all the way down to zero percent.

No matter how many independent cities you measure flooding in, you can never achieve a perfect 0 or 1 probability of (whatever), because the cities are independent.

We don't define "interesting" flooding in one city by reference to what happened in another city, so this situation is not described by the birthday paradox.