Sensitivity analysis of the Systeme Hydrologique Europeen for an upland catchment

Abstract

In order to study the accuracy with which parameter sets for physically-based distributed catchment models must be prepared and calibrated, a sensitivity analysis of the Système Hydrologique Européen was carried out based on simulations of two streamflow hydrographs for an upland catchment in mid-Wales. A single parameter was varied at a time and for each hydrograph the simulation sensitivity was assessed quantitatively in terms of the changes in peak discharge and in the root mean square value of the differences between measured and simulated discharges taken at intervals through the hydrograph. An important qualitative assessment was provided through interpretation of the changes based on physical reasoning. The results show that the simulations can be as sensitive to model grid spacing and time step as to catchment parameters and that these “structural” parameters should therefore be small by comparison with the scales of the variations which they are used to represent. Those catchment parameters to which the simulations are most sensitive (soil and flow resistance coefficients) can be evaluated with sufficient accuracy by point measurements at a few representative field sites, while the least important parameters (vegetation coefficients) can be evaluated using data from the literature. The scope for achieving equally satisfactory calibrations based on different combinations of parameter values is limited as long as several different hydrographs are considered. Similarly, for this particular application, the spatial distributions in rainfall and soil parameters have a relatively minor effect on the simulations.