Flood maps are needed for emergency response, research, and planning. The Height Above Nearest Drainage (HAND) technique is a low-complexity, terrain-based approach for inundation mapping from elevation, discharge-height relationship, and streamflow data. The recent operational capacities of the NOAA National Water Model (NWM) and pre-processed HAND products from the University of Texas offer an operational framework for real-time and forecast flood mapping across the United States. This paper offers the first detailed evaluation of the coupled NWM-HAND approach by comparing NWM-HAND simulations to a database of remotely sensed flood maps. These comparisons are made both quantitatively and through a detailed evaluation of selected results. The results show that NWM-HAND performs well in the majority of cases with 70 % of the calculated flood maps yielding an agreement of 80 % or better with the remote sensing observations. Persistent inaccuracies occur in lower-order reaches, regions of low relief, and when the NWM misses substantially either in magnitude or timing.
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Johnson et al. (2019) studied this question.