FEMA’s Flood Insurance Rate Maps are the most widely used flood risk maps in the U.S., but over 700 counties in the continental U.S. (CONUS) still lack them. As floods become more frequent and severe in recent years, there's an urgent need for faster, more flexible, and widely available flood risk tools. These tools should work at a national scale while also meeting local needs.

To help meet this need, we introduce a combined framework that uses the Design Flow Analysis Tool (DFAT) and the Urban Flooding Open Knowledge Network (UFOKN). This system estimates the depth of extreme floods (like 100-, and 500-year events) at the level of individual assets across 2.7 million+ catchments in CONUS. The only input the framework needs is a historical streamflow time series for the catchment in concern.

We tested this approach using retrospective streamflow data (1979–2022) from the National Water Model (NWM) version 2 and version 3 and found very good agreement in risk estimation with FEMA maps, especially in riverine and mountain areas. The framework is fast, scalable, and data-driven, offering infrastructure-level flood estimates to communities, planners and responders to better understand and prepare for extreme floods at unmapped locations.