Testing a climato-topographic index for predicting wetlands distribution along an European climate gradient

Knowledge of the spatial distribution of wetlands within landscapes is needed for a number of different purposes as non-point pollution control, aquatic life, flood protection or sediment traps or sources. The purpose of this paper was to propose and to test a parsimonious method for predicting wetlands in small catchments across a wide range of geological, topographic and climatic conditions. A climato-topographic index has been derived from the topographic index—taking into account the local slope and the upslope drainage area, first proposed by Beven and Kirkby [Hydrol. Sci. Bull. 24 (1979) 43]. This new index takes into account the effective rainfall, in addition to topographic factors, in order to achieve a prediction of wetland occurrence for places with different rainy conditions. The two indexes were compared. Six study areas were selected representing a wide range of climate, geology and geomorphology across Europe. The wetland area ranges from 1 to 30% of the total area for the different catchments, and the annual effective rainfall from 67 to 592 mm. The climato-topographic index seems able to predict the structure and general areal extent of wetlands without any local calibration of the model, except where the permeability of the soil surface is important and very different from the other sites considered. The climato-topographic index gives a classification of wetland occurrence similar to the field data. The exact location of the wetland is often poorly predicted, but this is mostly due to the current poor quality of the Digital Terrain Model. Thus, there is currently a technical limitation to the use of the approach advocated here.