Parameter sensitivity and uncertainty analysis of the WetSpa model using PEST

Abstract: The spatially distributed hydrologic model WetSpa is applied to the Torysa river basin (1297 km2) located in Slovakia. Daily hydrometeorological data from 1991 to 2000, including precipitation data from 14 stations, temperature data from 2 stations and evaporation data measured at one station are used as input to the model. The spatial characteristic of the basin are described by three base maps, i.e. DEM, landuse and soil type, in GIS form using 100 m cell size. Results of the simulations show a good agreement between calculated and measured hydrographs at the outlet of the basin. The model predicts the daily discharge values with a good accuracy, i.e. about 73 % according to the Nash-Sutcliff criterion. Sensitivity and uncertainty analysis of the model parameters is performed using a model-independent parameter estimator, PEST. It is found that the correction factor for calculating the actual evapotranspiration from potential evaporation has the highest relative sensitivity. Parameter uncertainty analysis gives an insight of a proper parameter set and parameter interval.