Modeling spatial patterns of saturated areas: A comparison of the topographic wetness index and a dynamic distributed model

SummaryTopography is often one of the major controls on the spatial pattern of saturated areas, which in turn is a key to understanding much of the variability in soils, hydrological processes, and stream water quality. The topographic wetness index (TWI) has become a widely used tool to describe wetness conditions at the catchment scale. With this index, however, it is assumed that groundwater gradients always equal surface gradients. To overcome this limitation, we suggest deriving wetness indices based on simulations of distributed catchment models. We compared these new indices with the TWI and evaluated the different indices by their capacity to predict spatial patterns of saturated areas. Results showed that the model-derived wetness indices predicted the spatial distribution of wetlands significantly better than the TWI. These results encourage the use of a dynamic distributed hydrological model to derive wetness index maps for hydrological landscape analysis in catchments with topographically driven groundwater tables.