Improved River Slope Datasets for the United States Hydrofabrics

The CONtiguous United States (CONUS) “Flood Inundation Mapping Hydrofabric - ICESat-2 River Surface Slope” (FIM HF IRIS) dataset integrates river slopes from the global IRIS dataset for 117,357 spatially corresponding main-stream reaches within NOAA’s Office of Water Prediction operational FIM forecasting system, which utilizes the Height Above Nearest Drainage approach (OWP HAND-FIM) to help warn communities of floods. To achieve this, a spatial joining approach was developed to align FIM HF reaches with IRIS reaches, accounting for differences in reach flowline sources. When applied to OWP HAND-FIM, FIM HF IRIS improved flood map accuracy by an average of 31% (CSI) across eight flood events compared to the original FIM HF slopes. Using a common attribute, IRIS data were also transferred from FIM HF IRIS to the CONUS-scale Next Generation Water Resources Modeling Framework Hydrofabric (NextGen HF), creating the NextGen HF IRIS dataset. By referencing another common attribute, SWOT vector data (e.g., water surface elevation, slope, discharge) can be leveraged by OWP HAND-FIM and NextGen through the two resulting datasets. The spatial joining approach, which enables the integration of FIM HF with other hydrologic datasets via flowlines, is provided alongside the two resulting datasets. If you use this dataset in your work, please cite: Chen, Y., Cohen, S., Baruah, A., Devi, D., Dhital, S., Tian, D., & Munasinghe, D. (2025). Merging Remote Sensing Derived River Slope Datasets with High-Resolution Hydrofabrics for the United States. Scientific Data, 12(1), 1657. https://www.nature.com/articles/s41597-025-05941-6 1. Version History FIM HF IRIS Version 1 - Version 3: Based on OWP HAND-FIM HF v4.5.2.11, SWORD v16 and IRIS v2.6. NextGen HF IRIS Version 1 - Version 3: Based on FIM HF IRIS v1.0 and NextGen HF v2.2, joined through the common fields, i.e., id, in both hydrofabrics. FIM HF IRIS Version v4: Based on OWP HAND-FIM HF v4.8.6.1, SWORD v17 and IRIS v3.2, joined using the improved RiverJoin spatial framework for better join performance (more complete extraction and fewer wrongly extracted reaches). NextGen HF IRIS Version v4: Will be based on NextGen HF v3.0, SWORD v17b and IRIS v3.3, using the RiverJoin framework. 2. Variable Description 2.1 FIM HF IRIS v4 HydroID: Unique identifier for FIM HF stream reaches From_Node: Upstream node ID To_Node: Downstream node ID reach_id: The SWORD reach identifier slope_iris_v3_2: The IRIS slope joined to the corresponding FIM HF flowline [mm/mm] slope_sword_v17: The SWORD slope joined to the corresponding FIM HF flowline [mm/mm] 2.2 NextGen HF IRIS v4 In production and will be uploaded soon!