Financial losses associated with US floods occur with surprisingly frequent, low return period precipitation

Flooding in the U.S. leads to billions of dollars in financial losses annually, with projected increases due to escalating extreme precipitation, population growth, and deteriorating flood infrastructure. While federal regulation mandates flood insurance purchase within 100-year floodplains, analysis of millions of federal insurance claims reveals that most flood losses arise from frequent, low-intensity precipitation events relative to regional climatology, with average regional precipitation return periods of under five years. Similarly, precipitation linked to disaster aid and property buyouts has return periods averaging less than 20 years. Using unsupervised learning, we identify that space-time precipitation clusters associated with major storms dominate losses, emphasizing the need for flood risk assessments and mitigation strategies that account for recurrent spatiotemporal compound events. The findings bring the putative 100-year flood protection strategy into question and provide a focal point for the ongoing national discussions that underscore systemic challenges in U.S. flood preparedness.