At present there are two global wetlands datasets that define the areal fraction of wetlands in a grid. The dataset developed by Cogley was presented in ISLSCP Initiative 1. The other dataset was developed by Matthews and Fung and has been widely used in climate modeling. Both datasets are available at 1 degree by 1 degree resolution. The two datasets are similar for many areas of the world, but for certain regions there are large differences, particularly in Alaska, Siberia and Eastern Asia. With a view to improving the performance of our global hydrological discharge model for the lateral flow of water on the continents, we have tested several parameterizations which include the influence of fractional wetlands area within a gridbox. In order to be able to judge the representativeness of the two datasets we have derived two sets of global parameters for the hydrological discharge model. The discharge model was then applied to five years of daily values of runoff and drainage which are taken from an ECHAM4-T42 simulation using climatological SST. The discharge of several large rivers was simulated with these different parameter sets. From the comparisons between the simulated discharges and the observed discharge of the considered rivers we judge the quality of the two datasets.