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 Erosion 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 from the Catsop catchment in the Netherlands shows that differences in measured and simulated hydrographs and sediment loads can be large. These differences may be caused by the sensitivity of the model to some of the input variables, such as saturated hydraulic conductivity and the initial soil moisture 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 part of the differences between measured and simulated data can be explained by these uncertainties. Thus, it is clear that detailed process-based models such as LISEM require very detailed and high-resolution input data in order to produce quantitative reliable results. The runoff processes in the Zululand catchment appeared to be dominated by slow throughflow and groundwater flow, which are processes that are not incorporated in LISEM.