A 100-year flood won't happen in my lifetime. True, a 100-year flood sounds like a freak once-in-a-lifetime event, but that's a 1% chance every single year.
The risk is cumulative. That 1% means over a 30-year mortgage. If the climate were stable, the odds of seeing at least one such flood are about one in four, and the climate is no longer stable.
Warmer air holds more moisture, driving more intense downpours. Rising seas push storm surges further inland, and more pavement and development shed water instead of absorbing it. Together, all these changes mean events labeled 1 in 100 years in the historical record can strike much more often in the future.