Calibrating and validating the LISEM model for two data sets from the Netherlands and South Africa

Within the framework of the GCTE Soil Erosion Network the Limburg Soil Eros ion Model (LISEM) has been tested and validated in two catchments in South- Limburg (the Netherlands) and Zululand (South Africa). The calibration and validation of the Green-Ampt version of the LISEM model using 10 storms fro m the Catsop catchment in the Netherlands shows that differences in measure d and simulated hydrographs and sediment loads can be large. These differen ces may be caused by the sensitivity of the model to some of the input vari ables, such as saturated hydraulic conductivity and the initial soil moistu re content. Given the uncertainty in the input maps of these variables and a limited number of point data that is used to create these maps, a large p art of the differences between measured and simulated data can be explained by these uncertainties. Thus, it is clear that detailed process-based mode ls such as LISEM require very detailed and high-resolution input data in or der to produce quantitative reliable results. The runoff processes in the Z ululand catchment appeared to be dominated by slow throughflow and groundwa ter flow, which are processes that are not incorporated in LISEM. (C) 1999 Elsevier Science B.V. All rights reserved.