HydroBASINS hydrological catchments (Level 04)

HydroBASINS represents a series of vectorized polygon layers that depict sub-basin boundaries at a global scale. The goal of this product is to provide a seamless global coverage of consistently sized and hierarchically nested sub-basins at different scales (from tens to millions of square kilometers), supported by a coding scheme that allows for analysis of catchment topology such as up- and downstream connectivity. HydroBASINS has been extracted from the gridded HydroSHEDS core layers at 15 arc-second resolution.

An important characteristic of any sub-basin delineation is the sub-basin breakdown, i.e. the decision of when and how to subdivide a larger basin into multiple tributary basins. At its highest level of sub-basin breakdown, HydroBASINS divides a basin into two sub-basins at every location where two river branches meet which each have an individual upstream area of at least 100 km². A second critical feature of sub-basin delineations is the way the sub-basins are grouped or coded to allow for the creation of nested sub-basins at different scales, or to navigate within the sub-basin network from up- to downstream. To support these functionalities and topological concepts, the ‘Pfafstetter’ coding system has been implemented in the HydroBASINS product offering 12 hierarchically nested sub-basin breakdowns globally.

The present collection provides the standard levels 3 to 6 of sub-basin breakdowns:

• Level 03 brings out the largest river basins such as the Amazon or the Congo river,
• Other levels progressively divide each basin into smaller tributaries.

HydroBASINS only includes a limited amount of (mostly geometric) attribute information, such as the sub-basin area, the distance from upstream headwaters and ocean outlet, and the Pfafstetter coding.

The HydroBASINS dataset and its Pfafstetter encoding are for example used in the nomenclature of SWOT vector features found in the Prior Lake Database collection and the Prior River Database collection.

For more information on HydroBASINS: