Advancement of the water footprint of Products and Regions in Concept, Operationalisation and Consideration of Spatially Explicit Water Availability

The supply of clean freshwater already poses challenges to some regions of the world and this situation is expected to worsen in the future. Improving water security is considered one of the major tasks of the 21st century. The Water Footprint (WF), used as umbrella term for established approaches, can contribute to this by correlating physical water use and water pollution with regional water availability and thus highlighting overuse. In order to derive directionally sound and meaningful recommendations for action, it is first necessary to address obstructive weaknesses and limitations of the WF approach. These include, in particular, the inconsistent treatment of supposedly different relevant water uses, an insufficient spatial resolution and the often narrow perspective of WF analyses. This cumulative dissertation aims to contribute to the reduction of these difficulties through conceptual work, highresolution, spatially explicit considerations and application of the WF at the level of society as a whole. Four publications are presented, which first create a coherent conceptual basis for the definition of quantitative and qualitative water use in the context of regional hydrology, enable a high spatial resolution of water use taking into account regional water availability, and identify the greatest possible starting points for improving water security by determining local hotspots in a global context. The concept of the Water Scarcity Footprint is primarily designed for an application in the context of Life Cycle Assessment (LCA) and can distinguish between direct water use at the location of a system under consideration and indirect water use within the upstream supply chains of the system (LCA-WSF). It is scalable and transferable to other applications, as also illustrated throughout the thesis. When embedding the LCA-WSF in an integrative analysis of key environmental impacts, a hotspot analysis can highlight where environmental sustainability is systematically neglected and help to ensure that improving only the water situation does not weaken the overall environmental performance. The conceptual framework is demonstrated through case studies of raw material extraction with a focus on lithium, renewable feedstock electricity generation and storage technologies as well as agricultural production for the German bioeconomy. The often limited data availability is reflected in partly high uncertainties, but main results are considered to be directionally sound. Future work and further developments of the WF approach should increasingly consider water use in mining and diffuse sources of water pollution, as well as contribute to the formulation of socially binding reduction targets for water use, so that the WF can fully unfold its potential for improving regional water security.