Modeling Approaches and Results

Abstract

Systems models have been a major methodologic part of many areas of study in science and engineering; they have certainly been an important focal point for our entire study. Over the period during which the Gotland study has been active, several quantitatively oriented models have been formulated. These models were modified and changed as data became available, different concerns gained precedence, or new ideas emerged. Although one of the aims of the Gotland project was to describe the island in some holistic systems formulation, this did not imply that our intention was to generate a very large and complex model that could incorporate all aspects of the entire system. It was felt that such an approach would rapidly become intractable, inflexible, and self-defeating. However, in the first phase of the project, an attempt was made to evaluate the major flows of energy, materials, and money within and between the natural and human systems to obtain an overall quantitative perspective for the entire island (Jansson and Zucchetto 1978a). At the time, the analysis included a mathematic simulation model incorporating hydrology and water quality considerations. Since then, the integration of different modeling efforts has become a main strategy of the project (Figure 3.1). Although it was initially anticipated that differential equation models would be used for all modeling efforts, the fact that many storages, such as capital, change relatively slowly in the economic system and that only certain types of economic data were reasonably accessible prompted us to adopt an input-output formulation for quantitative representation of the economic system; these are discussed later in this chapter in more detail.