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Technische Universität Berlin (2013)

Water footprint : assessing impacts of water use along product life cycles

Berger Markus

Titre : Water footprint : assessing impacts of water use along product life cycles

Der Wasserfußabdruck : Bewertung von Wassernutzung in Produktlebenszyklen

Auteur : Berger Markus

Université de soutenance : Technische Universität Berlin

Grade : Doctoral Thesis 2013

Freshwater scarcity is a relevant problem for more than 1 billion people around the globe. Therefore, the analysis of water consumption along the supply chain of products is of increasing relevance in current sustainability discussions. This thesis aims at enhancing the concept of water footprinting by reviewing and applying various water footprint approaches, identifying methodological challenges, and developing a novel water footprint method. In a comprehensive literature review more than 30 water footprint methods, tools, and databases have been identified and discussed. The scopes of water footprint approaches differ regarding the types of water use accounted for, the distinction of watercourses, the inclusion of quality aspects, and the consideration of temporal and regional aspects such as water scarcity and sensitivity of population or ecosystems. As the most advanced methods require the highest resolution inventory data, the trade-off between precision and applicability needs to be addressed in future database and method developments. As most of the water accounting and impact assessment methods have hardly been applied in practice, in this work a selection of methods has been tested in various case studies. Representing the first water footprint study of complex industrial products, water consumption and resulting impacts have been analyzed along the life cycles of Volkswagen’s car models Polo, Golf, and Passat. Based on inventory databases freshwater consumption throughout the cars’ life cycles has been allocated to material groups and assigned to countries according to import mix shares or location of production sites. By means of these regionalized water inventories, consequences for human health, ecosystems, and resources have been determined by using recently developed impact assessment methods. Water consumption along the life cycles of the three cars ranges from 52 – 83 m3/car. More than 95% of the water is consumed in the production phase, mainly resulting from producing iron, steel, precious metals, and polymers. Results show that water consumption occurs in 43 countries worldwide and that only 10% is consumed directly at Volkswagen’s production sites. Impacts on health tend to be dominated by water consumption in South Africa and Mozambique, resulting from the production of precious metals and aluminum. Consequences for ecosystems and resources are mainly caused by water consumption of material production in Europe. Based on the review and case studies, methodological challenges in water footprinting have been identified and potential solutions have been presented. A key challenge is the current definition of water consumption according to which evaporated water is regarded as lost for the originating drainage basin per se. Continental evaporation recycling rates of up to 100% within short time and length scales show that this definition is not valid and needs to be revised. Most impact assessment methods use ratios of annual withdrawal or consumption to availability to denote regional water scarcity. As these ratios are influenced by two metrics – withdrawal and availability – arid regions can appear uncritical if only small fractions of the little renewable supplies are used. Besides neglecting sensitivities to additional water uses, such indicators consider neither ground nor surface water stocks which can buffer water shortages temporally. Tackling the shortcomings of existing water footprint methods, the water accounting and vulnerability evaluation (WAVE) model has been developed. On the accounting level, atmospheric evaporation recycling within drainage basins is considered for the first time, which can reduce water consumption volumes by up to 33%. Rather than predicting impacts, WAVE analyzes the vulnerability of basins to freshwater depletion. Based on local blue water scarcity, the water depletion index (WDI) denotes the risk that water consumption can lead to depletion of freshwater resources. Water scarcity is determined by relating annual water consumption to availability in more than 11,000 basins. Additionally, WDI accounts for the presence of lakes and aquifers which have been neglected in water scarcity assessments so far. By setting WDI to the highest value in (semi-)arid basins, absolute freshwater shortage is taken into account in addition to relative scarcity. This avoids mathematical artefacts of previous indicators which turn zero in deserts if consumption is zero. As illustrated in a case study of biofuels, WAVE can help to interpret volumetric water footprint figures and, thus, promotes a sustainable use of global freshwater resources.

Mots clés : Verdunstungsrecycling ; Wasserfußabdruck ; Wassernutzung ; Wasserverbrauch ; Ökobilanz evaporation recycling ; life cycle assessment ; water consumption ; water footprint ; water use


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Page publiée le 23 octobre 2014, mise à jour le 29 décembre 2018