Analyzing Synthetic Stage‐Discharge Rating Curves and Riverine Flood Inundation Maps Derived From Global‐Scale Hydrologic and Hydraulic Modeling

ABSTRACT Synthetic rating curves (SRCs) are often used to translate streamflow forecasts into flood inundation maps. Previous studies have investigated the development and errors in SRCs at local, regional, and continental scales. In this analysis, we used the latest global methodology and datasets to develop SRCs for use in flood inundation map forecasting. Using the Yellowstone River Basin and the 2022 floods that affected the region, we analyzed the error in the SRCs assessment of stage and water surface elevation (WSE). We then investigated the error in flood inundation maps produced using the SRCs. Comparing SRCs to locally derived rating curves from 29 U.S. Geological Survey (USGS) stream gages, median error in SRC stage ranged from 0.45 to 0.65 m and SRC error was greatest at higher magnitude streamflows. This error increased to a median of 1.98–2.30 m when converting the stage to a WSE. After using the SRC WSE estimates to create an estimated flood inundation map, the WSE error at observed high‐water marks (1.99 m) was nearly proportional to average WSE error at the stream gage locations along the same river reach. Our results provide the first regional assessment of globally derived SRCs that are used in flood inundation mapping.