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HydroSHEDS


Hydro availabilty


  The HydroSHEDS data are being developed for all landmasses of the globe north of 56 south (i.e. excluding Antarctica). The HydroSHEDS package provides a suite of various raster and vector data sets, covering many of the common derivative products used in hydrological analyses. The data is prepared in seamless mode (no edge effects) and is provided as global or continental maps, or in five-degree by five-degree tile coverage.

  HydroSHEDS is produced on a continental basis. The drainage direction maps represent the core data layer from which users can derive their own products by applying standard GIS functionality. All other data layers are produced as time permits. Drainage direction maps are currently scheduled for completion as follows:

South AmericaComplete (May 2006)
AsiaComplete (March 2007)
Central AmericaComplete (March 2007)
AfricaComplete (October 2007)
AustraliaComplete (March 2008)
EuropeComplete (October 2008)
North AmericaComplete (January 2009)


  At this time, HydroSHEDS provides selected core and auxiliary data sets at 3 arc-second and 15 arc-second resolutions, including drainage directions and elevation surfaces. A vectorized stream network is available at 15 arc-second resolution only. Future data developments are scheduled to include basins; flow accumulations; slope; aspect; wetness index; stream orders; flow distances up- and downstream; as well as seamless global products at 30 arc-second and 5 minute resolution. Currently, the following data layers and resolutions are available:


5.1 Void-filled digital elevation model

Name signatureDEM
Data formatRaster
ValuesElevation in meters
(referenced to WGS84 EGM96 geoid)
ProjectionGeographic (latitude/longitude)
referenced to WGS84 horizontal datum
Available resolutions3 arc-second, 15 arc-second


  The elevation layers distributed with HydroSHEDS are based on a combination of the original SRTM-3 and DTED-1 elevation models of SRTM (for further specifications see 2.1 to 2.4 and 3.1). No-data voids have been filled using interpolation algorithms, and the data has been clipped at the ocean shoreline. Resolutions other than 3 arc-second are derived through aggregation (averaging): each upscaled data pixel is generated by averaging the corresponding neighborhood kernel of the 3 arc-second data. Note that for technical reasons HydroSHEDS elevation data show a consistent shift of 1.5 arc-seconds to the north and east as compared to original SRTM data (see 3.1.3).

  SRTM elevation data is provided in geographic projection (latitude/longitude) referenced to the WGS84 horizontal datum, and EGM96 vertical datum. Note that most global positioning systems use the WGS84 vertical datum as default. This difference in vertical datums may result in absolute elevation differences between +106 m and -86 m. For precise comparison of GPS elevation data with SRTM elevation data, conversion of the vertical datum should be considered beforehand.


5.2 Hydrologically conditioned elevation

Name signatureCON
Data formatRaster
ValuesElevation in meters
(referenced to WGS84 EGM96 geoid)
ProjectionGeographic (latitude/longitude)
referenced to WGS84 horizontal datum
Available resolutions3 arc-second


  The hydrologically conditioned elevation layers distributed with HydroSHEDS are the result of an iterative conditioning and correction process described in detail in section 3. For the specifics of the underlying digital elevation model see 5.1. Note that the conditioning process alters the original DEM and may render it incorrect for applications other than deriving drainage directions. Endorheic basins (inland sinks) are "seeded" with a no-data cell at their lowest point in order to terminate the flow.


5.3 Drainage directions

Name signatureDIR
Data formatRaster
ValuesDrainage directions in ESRI format (see below)
ProjectionGeographic (latitude/longitude) referenced to WGS84 datum
Available resolutions3 arc-second, 15 arc-second


  The drainage direction maps distributed with HydroSHEDS define the direction of flow from each cell in the conditioned DEM to its steepest down-slope neighbor. Values of flow direction vary from 1 to 128. All final outlet cells to the ocean are flagged with a value of 0. All cells that mark the lowest point of an endorheic basin (inland sink) are flagged with a value of -1. The flow direction values follow the convention adopted by ESRI's flow direction implementation:

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5.4 Flow accumulation (number of cells)

Name signatureACC
Data formatRaster
ValuesFlow accumulation in number of cells (see below)
ProjectionGeographic (latitude/longitude) referenced to WGS84 datum
Available resolutions15 arc-second


  The flow accumulation maps distributed with HydroSHEDS define the amount of upstream area (in number of cells) draining into each cell. The drainage direction layer is used to define which cells flow into the target cell. The number of accumulated cells is essentially a measure of the upstream catchment area. However, since the cell size of the HydroSHEDS data set depends on latitude, the cell accumulation value cannot directly be translated into drainage areas in square kilometers. A flow accumulation map reflecting true catchment areas is in preparation. Values range from 1 at topographic highs (river sources) to very large numbers (on the order of millions of cells) at the mouths of large rivers.


5.5 River network (stream lines)

Name signatureRIV
Data formatVector (lines)
ProjectionGeographic (latitude/longitude) referenced to WGS84 datum
Available resolutions15 arc-second
Line attributesIDunique identifier
Up_cellsmax. flow accumulation (number of cells) of stream reach


  The river network layers distributed with HydroSHEDS are directly derived from the drainage direction layers. The flow accumulation layer is used for selection and attribution. Only rivers with upstream drainage areas exceeding a certain threshold are selected: for the 15 arc-second resolution a threshold of 100 upstream cells has been used. The vectorized river reaches are currently attributed with the maximum flow accumulation (in number of cells) occurring within each river reach. More attributes will be added in future versions.


5.6 Drainage basins (watershed boundaries)

Name signatureBAS
Data formatVector (polygons)
ProjectionGeographic (latitude/longitude) referenced to WGS84 datum
Available resolutions15 arc-second
Polygon attributesIDunique identifier
Area_skmsurface area in square kilometers


The drainage basin layers distributed with HydroSHEDS are not yet finalized and will be provided at a later stage.

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Page Last Modified: January 28, 2009