Deep learning completes US flood hazard maps revealing millions exposed to previously unrecognized risk.

Flood maps are essential for disaster preparedness, insurance and climate adaptation, yet US official maps cover only one-third of river channels. Here we present a deep-learning framework that learns from existing records to produce a spatially complete 30-m flood hazard map for the contiguous US, filling unmapped regions and updating legacy extents. We estimate that the 2023 national database omits 11 million people and 4.1 million buildings in flood zones, adding 69% and 81% beyond the official baseline respectively. Crucially, our socioeconomic analysis of 917 cities reveals that entirely unmapped areas disproportionately harbor highly vulnerable demographics, particularly the elderly and children, exposing them to unrecognized risks and compounding existing inequalities. By solving the trilemma between accuracy, scale, and cost in national scale flood mapping, our open-source method broadens public access to risk information, paving the way for targeted and equitable climate adaptation.