Freshwater use and its consumption have emerged as areas of high environmental concern. The problems surrounding the management of this vital resource have stimulated public awareness, especially in the last decade. However, water use and related impacts are still widely excluded from Life Cycle Assessment (LCA) methodologies, which aim at measuring and assessing the environmentally relevant emissions and resources consumed, over the entire life cycle of a product or service: the supply chain, the product assembly, the use and disposal phase or recycling (ISO 14044). LCA is increasingly applied and required by industry, authorities and consumers to make sustainability decisions. One main reason of neglecting water has been the absence of comprehensive impact assessment methods associated with freshwater use. To overcome this obstacle, a method for assessing the environmental impacts of freshwater consumption was developed (Chapter 2). This method considers damages to three areas of protection: human health, ecosystem quality, and resources. The method can be used within most existing Life-Cycle Impact Assessment (LCIA) methods. For assessing the relative importance of water consumption, the method was integrated into the Eco-indicator-99 LCIA method and applied to a case study on worldwide cotton production. The importance of regionalized characterization factors for water use was also examined in the case study. In arid regions, water consumption may dominate the aggregated life-cycle impacts of cotton-textile production. Therefore, the consideration of water consumption is crucial in Life-Cycle Assessment (LCA) studies that include water-intensive products, such as agricultural goods. A regionalized assessment was shown to be necessary, since the impacts of water use vary greatly as a function of location.
While research on freshwater use has primarily focused on agriculture as the main water consumer, industrial water use has recently been discussed with more emphasis, and analysis is highly demanded from industries in general. Chapter 3 focuses on electricity production, which is involved in almost all economic activities. Electricity production claims the largest share of global industrial freshwater consumption. Different power production technologies were analysed and compared: Due to the global importance of hydropower and the high variability of its specific water consumption, a climate-dependent estimation scheme for water consumption in hydroelectric generation was derived. Applying national power production mixes, we analyzed water consumption and related environmental damage of the average power production for all countries. For the European and North American countries, electricity trade is also modelled for assessing the electricity market mix and the power-consumption related environmental damages. When applying the method for the impact assessment developed in Chapter 2, water consumption dominates the environmental damage of hydropower, but is generally negligible for conventional thermal, nuclear and alternative power production. The variability among country production mixes is substantial, both from a water consumption and overall environmental impact perspective.
Even more than energy production, agricultural goods are responsible for a large share of global water consumption and they represent important feedstocks in many product supply chain. Especially for food and bioenergy production, the relevance of the cropping phase heavily requires assessment of the most important crops. For regionalized impact assessment, inventory data on crop water consumption is lacking. In Chapter 4, the specific water consumption of 160 crops, covering 99.96% of globally harvested mass, is calculated. Additionally, as land and water resources are generally used on a trade-off basis, we also assessed land use for the production. In order to compare the water consumption and land use related impacts we apply indicators for land and water scarcity at a high geospatial resolution (5 arc minutes). Cultivation of wheat, rice, cotton, maize and sugar cane, which are the major sources of food, bioenergy and fiber, is the main driver for water scarcity on a global scale. For some crops, water scarcity impacts are inversely related to land resource stress, illustrating that water consumption is often at odds with land use. Maize, triticale and rice are currently the most efficient grains regarding combined land/water assessment, in terms of global averages. However, crop-specific average values are of little utility, as water consumption and land use are subject to high spatial variability. This large spread in water and land use related impacts underlines the importance of appropriate site selection for agricultural activities.
Besides the use for LCA studies, the detailed inventories and environmental impact assessment methods can be used for analyzing the consequences of global consumption of agricultural products. Such global assessments are also required for prospective assessments for policy making, especially under the aspect of population growth, increased meat consumption and bioenergy demand. In Chapter 5, four strategies to deliver the biotic output required to feed the globe in 2050 are developed and the associated environmental impacts on land and water resources are quantified. Precipitation regimes are modelled in the context of climate change, influencing irrigation and water stress. Based on the agricultural production pattern and related impacts of the different strategies we identified the trade-offs between land and water use. Intensification in arid regions currently under deficit irrigation can increase agricultural output by up to 30%. However, intensified crop production would lead to enormous water stress in many locations and might not be a viable solution. Suitable areas for expansion of agricultural land are mainly located in Africa, followed by South America. A combination of waste reduction with expansion on suitable pastures results as the best option, along with some intensification on selected areas. If in 2050, 1st generation biofuels additionally would replace 10% of current liquid fuel consumption, the added impact on land and water resources would double.
For allowing comparison of impacts due to land and water use within existing LCIA frameworks, an improved, regionalized impact assessment for land use was developed in Chapter 6, in addition to the water-consumption assessment method developed within Chapter 2. Generally, land use aspects dominate impact results of single-score assessment methods, for agricultural products. We therefore combined major land use approaches in LCA using the method Eco-indicator 99 as baseline, and adjusting it with regional factors for ecosystem vulnerability and net primary productivity on a high spatial resolution. The results reveal the global variability of land-water trade-offs in the impact of crop cultivation: In most regions, the impacts of land use outweigh those of water use, while in most arid zones the opposite case occurs, independent of the crop.
The thesis helps to substantially improve and enhance LCA and water footprinting by providing an advanced and operational method for impact assessment as well as high resolution inventory data for the most important water-consuming processes: agricultural production (160 individual crops) and electricity supply for 208 countries. For illustrating the application of the work developed above, a detailed water footprint case study on two food products is performed in Chapter 7: In a simple, yet meaningful way the results allow for quantitative comparisons between products, production systems and services in terms of their potential to contribute to water scarcity including an analysis of their supply chain. However, while the high resolution inventory results for water and land allow for better managing supply chains and comparison of products, it is still a generic assessment based on global datasets and models, not aiming to replace environmental impact assessment or detailed case studies. Interpretation of the results requires caution and identified hotspots might be verified in further research.
Institute of Environmental Engineering, ETH Zürich