A contribution to the environmental impact assessment of green water flows

In recent years, numerous efforts have been made to include water-related issues in life cycle assessment (LCA) methodology. This study provides an overview of existing methods that address green water use in LCA. In this overview, we analyse the main features of existing LCA methods used to examine changes in long-term blue water availability caused by variations in green water flows, particularly with respect to inventory, the characterisation model and characterisation factors. Moreover, we propose a method of assessing impacts on terrestrial green water flows (TGWI) and addressing reductions in surface blue water production (RBWP) caused by reductions in surface runoff due to land-use production systems. Both TGWI and RBWP are analysed, taking into account the green water use/atmosphere and green water use/soil interfaces. In this proposed method, the life cycle inventory (LCI) phase considers the net green water flow that leaves the land-use production system, allowing the study of two alternative reference land uses: 1) quasi-natural forest and 2) grasslands/shrublands. In the life cycle impact assessment (LCIA) phase, regional- and species-specific characterisation factors (CFs) for the amount of green water evaporated or transpired are also proposed. To illustrate the applicability of the proposed method, we employed a case study on Eucalyptus globulus stands (first rotation), located in Portugal. The results show that different impacts on terrestrial green water flows and on surface blue water production are obtained depending on the alternative reference land use. Moreover, the case study shows that the method developed can be a useful tool assisting in improved national E. globulus forest planning