Improvements in Continental-scale Flood Inundation Mapping at NOAA's Office of Water Prediction

The Office of Water Prediction (OWP) has been tasked with providing near real-time Flood Inundation Mapping (FIM) forecast services to the American public by the end of 2026. These FIM services are currently in an experimental phase wherein they are being supplied to 30% of the US population in order to both test their efficacy and train National Weather Service field office personnel on using FIM in their day-to-day Impact-Based Decision Support Services (IDSS).

OWP is currently using a multi-model approach that utilizes high-fidelity hydraulic models, like HEC-RAS, to supplement the terrain-based Height Above Nearest Drainage (HAND) model to produce a seamless continental FIM solution. The HAND approach has the benefit of being computationally fast and cost effective, which lends itself to being used in large-scale, temporally dense applications. However, a major source of flood extent inaccuracies comes from the Synthetic Rating Curves (SRCs) required to convert flows forecasted by the National Water Model into stages that can be mapped onto the landscape. In addition, the terrain hydroconditioning required to perform HAND can also negatively impact the skill of FIM services.

This presentation will cover the technical enhancements that are being made to improve the accuracy of the maps as well as tools being developed to increase their usability. These enhancements include: adjustments and calibration of the SRCs to better estimate river stage; addition of bathymetry information; utilization of nationally available bridge data to represent bridges; and terrain modifications that allow for more intuitive FIM interpretation. The platform to view public FIM and National Water Model forecasts is available at water.noaa.gov and the open-source code repository of the ongoing HAND development is at github.com/NOAA-OWP/inundation-mapping.