SWOT meets GRDC: Assigning SWORD nodes to in situ stations from the Global Runoff Data Centre

The Global Runoff Data Centre (GRDC) holds the most substantive collection of quality-assured river discharge data on a global scale, currently more than 11,900 stations. For rivers, the SWOT River Database (SWORD, Altenau et al. 2021) combines multiple global river- and satellite-related datasets to define nodes and reaches that will constitute SWOT river vector data products. Each SWORD node can be identified and accessed via its individual SWORD ID, which provides valuable information about the node's topology and type. The HYDROCRON website provides easy access via API to SWOT-derived time series of river characteristics, including water surface elevation, river width, and slope, as well as satellite-based discharge estimates at the reach level (https://podaac.github.io/hydrocron/intro.html). To facilitate the use of SWOT data in the vicinity of GRDC stations, we present a dataset that assigns SWORD nodes to GRDC stations based on SWORD v17b and v17c. For the matching, we used the corrected station coordinates (pour points) and calculated catchment areas derived from the GRDC watershed delineation (Färber et al. 2025). First, all SWORD nodes within a 1 km radius of the corrected station coordinates were considered as candidates, followed by an automated river name check. Subsequently the delineated GRDC catchment area was compared the upstream catchment area derived from the flow accumulation (MERIT Hydro) at the SWORD node. In addition, to account for potential spatial offsets between the SWORD node and the river channel, the maximum flow accumulation value within a 5×5 pixels window was considered. All area-based matches were reviewed manually and decided individually. Stations without an available catchment could not be compared by area but were manually checked. For 4,759 stations a SWORD node was assigned. Of these, 2,554 stations were matched by name, while 1,563 show agreement of the catchment area and the flow accumulation. In addition, 444 stations could be matched using the 5x5 pixels window method. 198 stations are assigned completely manual. For 7,163 stations no SWORD node was assigned: 6,972 have no SWORD node within 1 km, the remaining candidates (191) were rejected during manual review. Each record contains the SWORD node ID, the matching method as a quality indicator, name similarity, area difference and distance to the pour point, as well as node attributes (water surface elevation, width, maximum width). The assignments are identical for SWORD v17b and v17c; the two versions differ only in the distance from the river outlet (dist_out). The node ID and the reach ID allows direct retrieval of SWOT time series. Altenau et al., (2021) The Surface Water and Ocean Topography (SWOT) Mission River Database (SWORD): A Global River Network for Satellite Data Products. Water Resources Research. https://doi.org/10.1029/2021WR030054 Färber, C., Plessow, H., Mischel, S. A., Kratzert, F., Addor, N., Shalev, G., and Looser, U.: GRDC-Caravan: extending Caravan with data from the Global Runoff Data Centre, Earth Syst. Sci. Data, 17, 4613–4625, https://doi.org/10.5194/essd-17-4613-2025, 2025.