Original paper

Spatial pattern and temporal variability of runoff processes in Mediterranean Mountain environments - a case study of the Central Spanish Pyrenees

Butzen, Verena; Seeger, Manuel; Casper, Markus


Mediterranean mountain environments like the Central Spanish Pyrenees show a highly variable rainfall-runoff response, mainly explained by the intense intra- and inter-annual variability of precipitation yield. This leads to a highly differentiated moisture status and therefore it is assumed to lead also to highly variable runoff contributing areas.For the identification of areas with certain dominant runoff processes in an experimental headwater catchment in which agriculture was abandoned several decades ago the concept of the topographical index was extended by means of weighting grids. These weighting rasters were generated using additional information on soils and vegetation. Runoff generating areas were identified widespread in the catchment, with Hortonian overland flow (HOF) dominating the runoff processes on degraded soils, and saturation overland flow (SOF) dominating the footslope areas, where hydromorphic soils were mapped.Rainfall-runoff experiments were performed to quantify runoff and erosion and to identify seasonal changes using experimental data gained in different seasons of the year. The seasonal changes in runoff response could be localised clearly within the areas of SOF, whereas the other ones showed a similar behaviour. This implied that the procedure of delineation had to be differentiated for dry and moist conditions, and that the SOF areas had to be reclassified as SSF/DP areas for dry conditions. Due to the location of these areas close to the ravine, we could explain the pronounced switching runoff behaviour of the catchment.GIS techniques combining different levels of topographic, soil and vegetation information showed to be suitable for delineation of areas with different runoff generation processes. The inclusion of seasonally distributed experimental data demonstrated that for dry conditions, slightly different methods have to be applied. Nevertheless, the study showed also the limitations of the combined methods: (I) subsurface flows and ground water recharge could only be deduced, not demonstrated, (II) finally, there is still a good knowledge of the area needed for an accurate process representation.


mediterranean mountainsrunoff generation processesgistopographic indexrainfall experiments