Table 1 shows the annual discharge and the size of the catchment area for some of the corresponding rivers. Both values are related to a catchment upstream from a certain discharge measuring station. The discharge data (presented in Dümenil et al., 1993) were provided by the Global Runoff Data Centre (GRDC) with the exception of data related to the Baltic Sea (Bergström and Carlsson, 1993).

 

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For such a comparison of catchment areas we have to define the real catchments and the model catchments of the largest rivers of the world at a grid resolution of 0.5 degree. The real catchments are taken from a global dataset which we have derived from a catchment dataset of the US Army Corps of Engineers. This original dataset was modified to eliminate a lot of inconsistencies. It was improved with the help of maps and observed river paths of the CIA (1992). The distribution of 35 of the largest catchments of the world is shown above.

A catchment dataset at 0.5 degree resolution

For model validation and for the development of parameterizations the simulated discharge has to be compared with the observed discharge of a number of large rivers of the world. With a view to minimize the model error it is important that the real catchment area of a specific river agrees well with the model catchment area as given by the model topography. If this is not the case this may cause a systematic under- or overrepresentation of volume and timing of the flow.