A fuzzy-based approach for characterization of uncertainties in emergy synthesis: an example of paved road system

Emergy synthesis is capable of quantifying environmental resources and services, as well as economic and human services, that are used up directly or indirectly to make a product available. However, a controversial aspect of emergy synthesis is the lack of research characterizing and documenting uncertainties in the emergy evaluation process. Uncertainty can arise from analysis of numerous components and flows in a complex environmental system. The reliability of emergy synthesis results may be undermined by both the inherent uncertainty of emergy parameters and models, and by a lack of knowledge regarding the certainty of resulting outputs. This paper explores the utility of fuzzy-based methods in emergy synthesis. Applying fuzzy set theory facilitates the gradual assessment of Unit Emergy Values (UEVs) as a set of possible UEVs. In other words, uncertainty of UEVs is described with the aid of a membership function valued in the real unit interval [0, 1]. The proposed fuzzy-based emergy synthesis has been applied for Life Cycle Assessment (LCA) of a transportation infrastructure system. A paved road, with different pavement options (i.e. asphalt and concrete), has been selected as a case study to highlight the impacts of propagation of different sources of uncertainties in the emergy evaluation process and decision making. Results indicate that fuzzy-based modeling can provide better insight for both emergy and LCA practitioners. The developed methodology provides transparency that should be an integral part of an emergy-based decision making process.