Uniqueness of place and process representations in hydrological modelling

This paper addresses the problem of uniqueness of catchment areas in relati on to model representations of flow processes. The uniqueness of field meas urements as a limitation on model representations is discussed. The treatme nt of uniqueness as a residual from a modelled relationship may conceal inf ormation about the uniqueness of catchments, while the treatment of uniquen ess as a set of parameter values within a particular model structure is pro blematic due to the equifinality of model structures and parameter sets. Th e analysis suggests that a fully reductionist approach to describe the uniq ueness of individual catchment areas by the aggregation of descriptions of small scale behaviour will be impossible given current measurement technolo gies. A suggested strategy for the representation of uniqueness of place as a fuzzy mapping of the landscape into a model space is suggested. This wil l lead to a quantification of the uncertainty in predictions of any particu lar location in a way that allows a conditioning of the mapping on the basi s of the available data. This process can incorporate a hypothesis testing approach to model evaluation but the problem of multiple behavioural models may provide an ultimate limitation on the realism of process representatio ns: not on the principle of realism but on the possibility of unambiguous p rocess representations.