An improved parameter estimation procedure in lake modelling

This paper proposes an alternative parameter estimation procedure. Usually the parameters that yield the highest sensitivity are calibrated by trial and error or by an automatic calibration procedure. If the number of parameters to be calibrated is more than 3-5, this procedure is very time consuming. The presented procedure is based on the assumption that the biological components in an ecosystem model attempt to develop such properties that they become best possible survivors, i.e. develop as much biomass as possible. It has previously been proposed that the survival of the entire ecosystem can be measured by use of the thermodynamic function exergy, which measures the distance from thermodynamic equilibrium and accounts for the biomass and its information content. If these assumptions are correct, it should be possible to determine the combination of parameters which gives the highest exergy. The paper presents the use of this idea in combination with a normal calibration. The parameters, which are less known from the literature and still yield a relatively high sensitivity, are determined by use of the above-mentioned exergy principle. The parameters that are known within relatively narrow ranges from the literature are calibrated by the normal procedure. The method has been used on a concrete lake modelling study and given good results. This combination method seems therefore to offer clear advantages, particularly for models with a relatively high number of sensitive parameters (> 5), which otherwise would require a very cumbersome calibration.