How to understand water scarcity results as a Life Cycle Assessment practitioner? An investigation into evaporation values and characterisation factors applied on reservoir-based hydroelectricity

Purpose: This article serves to evaluate and increase the understanding of water footprint results when using recommended impact categories available for Life Cycle Assessment (LCA) practitioners. Results are exemplified by analyses of reservoir hydroelectricity with regard to local net evaporation and water scarcity conditions. Methods: An existing Norwegian hydropower plant with connecting reservoirs has been ‘moved’ virtually to several locations in order to evaluate different conditions concerning evaporation rates and water scarcities. The study is based on LCA methodology, as standardised in ISO 14044 and other literature, as well as ISO 14046 for water footprinting. The functional unit is 1 kWh electricity produced from reservoir hydropower and thereafter distributed to the point of use. Net evaporative losses have been employed. The results are presented for the categories water footprint inventory and water scarcity footprint, using the ReCiPe 2016 Midpoint and AWARE methods, as implemented by SimaPro. Results and discussion: Regions have varying levels of evaporation and are more or less water scarce, but these two dimensions are not necessarily correlated. Hence, a reservoir-based hydropower plant’s most burdensome value chain activity might vary depending on the location and the chosen impact category. For water scarcity footprint, the site-specific net evaporation rates have in general more importance than the site-specific water scarcity factors. Conclusions: Both the LCA-based water footprint inventory and the water scarcity footprint are key impact categories in the context of water consumption. They address different facets and are both critical for grasping how local conditions shape the effects of water use. This insight is especially important when using off-the-shelf LCIA methods, without taking time-dependent scarcity factors into account. The study has identified inconsistencies in the literature regarding calculation methods for water footprint inventories and water scarcity footprint. Future studies should aim to include a broader range of locations and employ more spatially explicit and detailed characterisation factors.