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106 ience ence a r t i c l e i n f o Topography 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 differ-(Houser et al., 1998). Topography provides an alternative for mapping wetlands and spatial patterns of wetness in catchments where the assumption that groundwater tables basically follow topography holds (Haitj-ema and Mitchell-Bruker, 2005). The topographic wetness index (TWI) (Beven and Kirkby, 1979) relates upslope area as a measure over time. In situations where meteorological and hydrological data are available in addition to a digital elevation model (DEM), a more dynamic approach might be useful. Distributed hydrologi-cal models allow dynamic simulations of spatially distributed water storage that can be used to derive alternative wetness indi-ces. These model-based wetness indices (MWIs) account, unlike the static TWI, for dynamic influences of upstream and down-stream conditions. Thus, they are also applicable in flat terrain where groundwater gradients can be significantly different from ground surface slopes