There is a link to the full report included with the summary above.
The bottom line is that it is raining and flooding much more frequently than in the past due to warming earth temperatures that hold more moisture. This means “that approximately 17.7 million properties across the country are at substantial risk or greater (1-in-100-year risk or greater), which is 2.2 times more than the amount included in the FEMA 1-in-100 SFHA designation.”
Homes that have never flooded in the past are flooding — and have no flood insurance.