Upscaling discrete internal observations for obtaining catchment-averaged TOPMODEL parameters in a small Mediterranean mountain basin

Discrete observations on recession flows, local depth to the water table and the extent of saturated areas were used in the Vallcebre small research basin for obtaining the distribution functions of the TOPMODEL catchment parameters that drive the behaviour of the saturated store. Using this parameter information within GLUE framework, the robustness of discharge simulations was improved and the uncertainty of flow separation between two components was significantly reduced when compared with the results obtained with customary calibration with flow data at the outlet. Nevertheless, the analysis of the uncertainty in the determination of the local value of the topographic index at the piezometer location demonstrated that this may be a relevant limitation of the approach, particularly for high values of the topographic index, and a careful selection of the piezometer is recommended. The use of the extent of saturated areas provided the best and more representative results, although the simulated patterns of saturated areas did not match well the observed ones, because the role of local controls beyond the topographic index.