Petra Döll and Bernhard Lehner

The global drainage direction map DDM30 is a raster map which describes the drainage directions of surface water with a spatial resolution of 30’ longitude by 30’ latitude. 66896 individual grid cells, covering the entire land surface of the globe (without Antarctica), are connected to each other by their respective drainage direction and are thus organized into drainage basins. Each cell can drain only into one of the eight neighboring cells.

DDM30 is based on 1) the digital drainage direction map with a resolution of 5’ of Graham et al. (1999) for South America, Australia, Asia and Greenland, and 2) the HYDRO1k digital drainage direction map (as flow accumulation map) with a resolution of 1 km (USGS, 1999) for North America, Europe, Africa and Oceania (without Australia).

Both given base maps were upscaled to a resolution of 30’. The resulting drainage direction map was manually corrected using the vectorized river data sets of ESRI (1992) and ESRI (1993), various atlases and the location and drainage basin sizes of 935 river discharge gauging stations from the GRDC (1999). In the course of the manual corrections, the drainage directions of 35% of the grid cells were changed.

A more detailed documentation and validation of DDM30 is provided in Döll, P., Lehner, B. (2002): Validation of a new global 30-min drainage direction map. Journal of Hydrology, 258(1-4), 214-231.

References

• ESRI (1992): ArcWorld 1:3 M Continental Coverage.
• ESRI (1993): Digital Chart of the World 1:1 M.
• Graham, S.T., Famiglietti, J.S., Maidment, D.R. (1999): Five-minute, 1/2° and 1° data sets of continental watersheds and river networks for use in regional and global hydrologic and climate system modeling studies. Water Resour. Res. 35, 583-587.
• GRDC (Global Runoff Data Centre) (1999): Observed river discharges. Global Runoff Data Centre, D-56068 Koblenz, Germany.
• USGS (1999): HYDRO1k Elevation Derivative Database. Eros Data Centre.

If you wish to obtain the data set, please contact Prof. Dr. Petra Döll.