A case study on qualitative model evaluation using data about river water quality

Qualitative reasoning has been successfully used for ecological modelling, particularly when numerical data are not available. However, in order to further explore the potential of this modelling approach, it is important to discuss how to incorporate numerical data, if available, and to develop means to evaluate conceptual aspects and model outputs. This paper describes a study on qualitative model evaluation, in which numerical data about water quality are used to define different scenarios in a water basin, so that the outputs of simulations with the model can be compared to the actual system. The model was evaluated by independent experts, concerning its conceptual and operational aspects, and with respect to its predictive capability. The model was considered valid for the intended use, which is to increase the understanding of non-expert water managers. Water quality Water resources management 1. Introduction Are models truthful representations of ecological systems? As the use of models as tools for decision making and public policy formulation is quickly increasing, concern about the correctness of model outputs grows. However, there are no universally accepted rules for model evaluation — and semantic, philosophical and practical aspects of the evaluation process have been subject of a thorny discussion (for an overview on this discussion see, for example, Konikow and This paper describes a case study on model validation, more specifically, qualitative model validation. The model evaluated here was developed with techniques of Qualitative Reasoning (QR), an area of Artificial Intelligence that deals with symbolic representations of continuous properties of physical systems using incomplete knowledge (see Weld and de Kleer, 1990; see also the special issue of AI Magazine, volume 24, 2003, for an overview on state-of-the-art QR). The model describes the Monteiro river water basin, a small basin located near Brasilia, in the Federal District, Brazil. This basin was selected because it presents great diversity of land uses: protected areas, agricultural activities, consolidated urban areas and areas undergoing consolidation. Details about the study area, the model and the evaluation process can be found in Araújo (2005). The work described here aims at answering the following research question: is the knowledge captured in the model capable of reproducing the qualitative behaviour of dissolved oxygen concentration under the influence of different land uses in the Monteiro river basin? The paper is organized as follows: initially, the fundamentals of qualitative reasoning models are presented and, in Section 3, model evaluation is briefly …