Planetary boundaries for water - A review

The water planetary boundary has been proposed to determine limits for a sustainable anthropogenic appropriation of freshwater. Aim of the present research was to summarise the water planetary boundary's development status and applications including its integration into Life Cycle Assessment and Environmentally-Extended Input-Output-Analysis. A systematic literature review was conducted for studies featuring the keywords "planetary boundary" and "water consumption". All pertinent studies were categorised as either revision, commentary, stand-alone application, the application within Life Cycle Assessment or application within Environmentally-Extended Input-Output Analysis and subsequently summarised and discussed. Overall, 35 studies from the period of 2009 until mid-2020 are subject of this review. Recent advancements such as spatially differentiated thresholds and refined sub-boundaries have addressed initial shortcomings of the concept of a water planetary boundary. Stand-alone applications of the water planetary boundary have either established local thresholds or allocated fair shares of afore-defined global thresholds. Several authors integrated the concept of a water planetary boundary into LCA e.g. via characterisation factors, weighting or normalisation, often under consideration of sharing principles. An application of the water planetary boundary into Environmentally-Extended Input-Output Analysis is less represented although some authors have demonstrated its powerfulness in investigating causes for the exceedance of local thresholds. For some of the reviewed studies, a link to the water planetary boundary remains rather vague as these studies merely investigate water availability in comparison to consumption. Although it should be applied with caution, the concept of a planetary boundary for freshwater use can contribute to understanding limits to sustainable freshwater consumption. Many studies established water use thresholds but refrained from analysing causative drivers in detail. Challenges for exploring this further include overcoming spatial and temporal mismatches of environmentally-extended economic accounts and hydrogeological data.