Sensitivity analysis and multi-response, multi-criteria evaluation of a physically based distributed model

A sensitivity study of the subsurface flow component of the physically based distributed modelling system SHETRAN using data from a small Mediterranean mountain catchment is presented. The parameter space sampled was based on ranges of parameter values measured in field experiments. Model results were validated by comparison against outlet discharge, soil moisture reserve and phreatic surface level, using a number of criteria. The objectives of this exercise were: to explore variability in simulation response produced by uncertainty in parameter values to use internal data to examine process representation within the models and to attempt to reduce uncertainty in parameter estimates through use of a number of response variables and a number of criteria in model evaluation. A wide range of responses Were produced from across the parameter space sampled. Furthermore, the sensitivity analysis demonstrated that interactions between parameters are complex, and that the sensitivity of individual parameters changed according to the values taken by other parameters and to the state of the system. The multi-response, multi-criteria evaluation presented herein exposed the presence of compensating errors within the model, which conventional procedures, which only consider outlet discharge, might fail to detect. This showed that parameter optima occurred in different parts of the parameter space for each of the response variables considered, although it did show that there was a region of the parameter space in which acceptable results were found for all responses. It is suggested that the fact that parameter optima were found in different parts of the parameter space for different responses indicates incorrect estimation of those model parameters not considered as part of the sensitivity study or omissions in the process representation embodied within the current SHETRAN subsurface flow model. (C) Copyright 2002 John Wiley Sons, Ltd.