HydroBASINS

This section provides only a brief overview of the HydroBASINS product.

For more information on HydroBASINS please refer to the HydroBASINS Technical Documentation.

You can download HydroBASINS data here.

Background

HydroBASINS is a series of polygon layers that depict watershed boundaries and sub-basin delineations 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 watershed topology such as up- and downstream connectivity.

Using the HydroSHEDS database at 15 arc-second resolution, watersheds were delineated in a consistent manner at different scales, and a hierarchical sub-basin breakdown was created following the topological concept of the Pfafstetter coding system. The resulting polygon layers are termed HydroBASINS and represent a subset of the HydroSHEDS database.

The HydroBASINS product has been developed on behalf of World Wildlife Fund US (WWF), with support and in collaboration with the EU BioFresh project, Berlin, Germany; the International Union for Conservation of Nature (IUCN), Cambridge, UK; and McGill University, Montreal, Canada.

HydroBASINS is covered by the same License Agreement as the HydroSHEDS database.

Citations and acknowledgements of the HydroBASINS data should be made as follows:

Lehner, B., Grill G. (2013): Global river hydrography and network routing: baseline data and new approaches to study the world’s large river systems. Hydrological Processes, 27(15): 2171–2186. Data is available at www.hydrosheds.org.

Methods

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. Standard GIS tools offer the possibility to break out sub-watersheds at any confluence where the inflowing branches (i.e., a tributary and its main stem) exceed a certain size threshold, typically measured as the number of upstream pixels or the upstream catchment area. HydroBASINS follows the same concept and 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 breakout of nested sub-basins at different scales, or to navigate within the sub-basin network from up- to downstream. One of the easiest methods for navigation is to provide the ID of the next downstream object, which allows for moving from object to object in order to traverse the network. As for nesting and topological concepts, the ‘Pfafstetter’ coding system is frequently used due to its relative simplicity and ease of application. The basic principle of the Pfafstetter coding is that a larger basin is sequentially subdivided into 9 smaller units (the 4 largest tributaries, coded with even numbers, and the 5 inter-basins, coded with odd numbers). Thus, the next finer resolution of a sub-basin delineation is achieved at the next Pfafstetter level by adding one digit to the code of the previous level. A more detailed description of the Pfafstetter coding is provided in literature (e.g., Verdin and Verdin 1999). The HydroBASINS product follows the Pfafstetter concept and provides levels 1 to 12 globally.

Formats

Version 1.c of HydroBASINS was developed in two formats:

In Format 1 (standard; without lakes), all sub-basins follow the standard concept of nested watersheds and are strictly derived from the underlying flow direction grids of HydroSHEDS by applying the area thresholds and Pfafstetter concept as described above. Format 1 consists of 12 individual polygon layers representing the 12 Pfafstetter levels. Additionally, an extra layer (Level 0) is provided which includes all sub-basins at their smallest breakdown with the full coding sequence of levels 1-12 in the attribute table. Users can derive any Pfafstetter level directly from the 'Level 0' layer by dissolving the sub-basin polygons based on the desired level code.

Format 2 (customized; with inserted lakes) was designed to specifically accommodate the special requirements of the BioFresh project and was produced in collaboration with IUCN. This dedicated version follows the same concept as the standard format, yet a global lake layer was integrated into the data. Lake polygons were taken from the Global Lakes and Wetlands Database (GLWD; Lehner and Döll 2004) and were clipped into the sub-basin polygons of HydroBASINS. Format 2 has a more complext coding structure than Format 1, and no 'Level 0' is provided.

HydroBASINS data are provided as regional tiles in individual polygon shapefiles, one for each region and each Pfafstetter level (see below figure for regional extents). It should be noted that the quality of the HydroSHEDS data is significantly lower for regions above 60 degrees northern latitude as there is no underlying SRTM elevation data available and thus a coarser scale DEM has been inserted (HYDRO1k provided by USGS).

©2016 World Wildlife Fund, Inc.