Stephan Pfister

Review of methods addressing freshwater use in life cycle inventory and impact assessment

PurposeIn recent years, several methods have been developed which propose different freshwater use inventory schemes and impact assessment characterization models considering various cause–effect chain relationships. This work reviewed a multitude of methods and indicators for freshwater use potentially applicable in life cycle assessment (LCA). This review is used as a basis to identify the key elements to build a scientific consensus for operational characterization methods for LCA.MethodsThis evaluation builds on the criteria and procedure developed within the International Reference Life Cycle Data System Handbook and has been adapted for the purpose of this project. It therefore includes (1) description of relevant cause–effect chains, (2) definition of criteria to evaluate the existing methods, (3) development of sub-criteria specific to freshwater use, and (4) description and review of existing methods addressing freshwater in LCA.Results and discussionNo single method is available which comprehensively describes all potential impacts derived from freshwater use. However, this review highlights several key findings to design a characterization method encompassing all the impact pathways of the assessment of freshwater use and consumption in life cycle assessment framework as the following: (1) in most of databases and methods, consistent freshwater balances are not reported either because output is not considered or because polluted freshwater is recalculated based on a critical dilution approach; (2) at the midpoint level, most methods are related to water scarcity index and correspond to the methodological choice of an indicator simplified in terms of the number of parameters (scarcity) and freshwater uses (freshwater consumption or freshwater withdrawal) considered. More comprehensive scarcity indices distinguish different freshwater types and functionalities. (3) At the endpoint level, several methods already exist which report results in units compatible with traditional human health and ecosystem quality damage and cover various cause–effect chains, e.g., the decrease of terrestrial biodiversity due to freshwater consumption. (4) Midpoint and endpoint indicators have various levels of spatial differentiation, i.e., generic factors with no differentiation at all, or country, watershed, and grid cell differentiation.ConclusionsExisting databases should be (1) completed with input and output freshwater flow differentiated according to water types based on its origin (surface water, groundwater, and precipitation water stored as soil moisture), (2) regionalized, and (3) if possible, characterized with a set of quality parameters. The assessment of impacts related to freshwater use is possible by assembling methods in a comprehensive methodology to characterize each use adequately.

COMPARISON OF BOTTOM-UP AND TOP-DOWN APPROACHES TO CALCULATING THE WATER FOOTPRINTS OF NATIONS

The water footprint has been introduced as a potential sustainability indicator for human-induced water consumption, and has frequently been studied at local, national and international scales during the last decade. While water footprints are sometimes understood as a measure that includes environmental impact assessment, the water footprint as used in this paper refers to volumes of water consumed, without including weighting procedures to allow for the assessment of impacts. Two types of approaches have been applied to calculate the water footprint in the literature: bottom-up and top-down approaches. This study compares and discusses advantages and limitations of the water footprint of nations based on two input–output top-down approaches (Water Embodied in Bilateral Trade (WEBT) and Multi-regional Input–Output Analysis (MRIO)) and of the existing national water footprint accounts from the literature based on the bottom-up approach. The differences in the bottom-up and WEBT approaches are caused by inter-sectoral cut-off, because bottom-up approaches do not consider the entire industrial supply chains, while the WEBT method covers the water footprint by tracing the whole domestic supply chain of each country. The differences in the WEBT and MRIO approaches are due to an inter-regional cut-off effect, as the WEBT approach only traces domestic supply chains whereas the MRIO approach traces entire global supply chains. We found that both bottom-up and top-down approaches are heavily dependent on the quality of existing datasets, and differ substantially. The total water footprints of nations based on different approaches vary by up to 48%, and this variation is even larger at the sector level.

Environmental impacts of water use in global crop production: hotspots and trade-offs with land use.

Global crop production is causing pressure on water and land resources in many places. In addition to local resource management, the related environmental impacts of commodities traded along international supply chains need to be considered and managed accordingly. For this purpose, we calculate the specific water consumption and land use for the production of 160 crops and crop groups, covering most harvested mass on global cropland. We quantify indicators for land and water scarcity with high geospatial resolution. This facilitates spatially explicit crop-specific resource management and regionalized life cycle assessment of processed products. The vast cultivation of irrigated wheat, rice, cotton, maize, and sugar cane, which are major sources of food, bioenergy, and fiber, drives worldwide water scarcity. According to globally averaged production, substituting biofuel for crude oil would have a lower impact on water resources than substituting cotton for polyester. For some crops, water scarcity impacts are inversely related to land resource stress, illustrating that water consumption is often at odds with land use. On global average, maize performs better than rice and wheat in the combined land/water assessment. High spatial variability of water and land use related impacts underlines the importance of appropriate site selection for agricultural activities.

A new water footprint calculation method integrating consumptive and degradative water use into a single stand-alone weighted indicator

PurposeA complete assessment of water use in life cycle assessment (LCA) involves modelling both consumptive and degradative water use. Due to the range of environmental mechanisms involved, the results are typically reported as a profile of impact category indicator results. However, there is also demand for a single score stand-alone water footprint, analogous to the carbon footprint. To facilitate single score reporting, the critical dilution volume approach has been used to express a degradative emission in terms of a theoretical water volume, sometimes referred to as grey water. This approach has not received widespread acceptance and a new approach is proposed which takes advantage of the complex fate and effects models normally employed in LCA.Methods Results for both consumptive and degradative water use are expressed in the reference unit H2Oe, enabling summation and reporting as a single stand-alone value. Consumptive water use is assessed taking into consideration the local water stress relative to the global average water stress (0.602). Concerning degradative water use, each emission is modelled separately using the ReCiPe impact assessment methodology, with results subsequently normalised, weighted and converted to the reference unit (H2Oe) by comparison to the global average value for consumptive water use (1.86 × 10−3 ReCiPe points m−3).Results and discussionThe new method, illustrated in a simplified case study, incorporates best practice in terms of life cycle impact assessment modelling for eutrophication, human and eco-toxicity, and is able to assimilate new developments relating to these and any other impact assessment models relevant to water pollution.ConclusionsThe new method enables a more comprehensive and robust assessment of degradative water use in a single score stand-alone water footprint than has been possible in the past.

Life Cycle Inventory and Carbon and Water FoodPrint of Fruits and Vegetables: Application to a Swiss Retailer

Food production and consumption is known to have significant environmental impacts. In the present work, the life cycle assessment methodology is used for the environmental assessment of an assortment of 34 fruits and vegetables of a large Swiss retailer, with the aim of providing environmental decision-support to the retailer and establishing life cycle inventories (LCI) also applicable to other case studies. The LCI includes, among others, seedling production, farm machinery use, fuels for the heating of greenhouses, irrigation, fertilizers, pesticides, storage and transport to and within Switzerland. The results show that the largest reduction of environmental impacts can be achieved by consuming seasonal fruits and vegetables, followed by reduction of transport by airplane. Sourcing fruits and vegetables locally is only a good strategy to reduce the carbon footprint if no greenhouse heating with fossil fuels is involved. The impact of water consumption depends on the location of agricultural production. For some crops a trade-off between the carbon footprint and the induced water stress is observed. The results were used by the retailer to support the purchasing decisions and improve the supply chain management.

GIS-Based Regionalized Life Cycle Assessment: How Big Is Small Enough? Methodology and Case Study of Electricity Generation

We describe a new methodology for performing regionalized life cycle assessment and systematically choosing the spatial scale of regionalized impact assessment methods. We extend standard matrix-based calculations to include matrices that describe the mapping from inventory to impact assessment spatial supports. Uncertainty in inventory spatial data is modeled using a discrete spatial distribution function, which in a case study is derived from empirical data. The minimization of global spatial autocorrelation is used to choose the optimal spatial scale of impact assessment methods. We demonstrate these techniques on electricity production in the United States, using regionalized impact assessment methods for air emissions and freshwater consumption. Case study results show important differences between site-generic and regionalized calculations, and provide specific guidance for future improvements of inventory data sets and impact assessment methods.

Virtual Scarce Water in China

Water footprints and virtual water flows have been promoted as important indicators to characterize human-induced water consumption. However, environmental impacts associated with water consumption are largely neglected in these analyses. Incorporating water scarcity into water consumption allows better understanding of what is causing water scarcity and which regions are suffering from it. In this study, we incorporate water scarcity and ecosystem impacts into multiregional input-output analysis to assess virtual water flows and associated impacts among 30 provinces in China. China, in particular its water-scarce regions, are facing a serious water crisis driven by rapid economic growth. Our findings show that inter-regional flows of virtual water reveal additional insights when water scarcity is taken into account. Consumption in highly developed coastal provinces is largely relying on water resources in the water-scarce northern provinces, such as Xinjiang, Hebei, and Inner Mongolia, thus significantly contributing to the water scarcity in these regions. In addition, many highly developed but water scarce regions, such as Shanghai, Beijing, and Tianjin, are already large importers of net virtual water at the expense of water resource depletion in other water scarce provinces. Thus, increasingly importing water-intensive goods from other water-scarce regions may just shift the pressure to other regions, but the overall water problems may still remain. Using the water footprint as a policy tool to alleviate water shortage may only work when water scarcity is taken into account and virtual water flows from water-poor regions are identified.

Projected water consumption in future global agriculture: Scenarios and related impacts

Global stress on water and land resources is increasing as a consequence of population growth and higher caloric food demand. Many terrestrial ecosystems have already massively been degraded for providing agricultural land, and water scarcity related to irrigation has damaged water dependent ecosystems. Coping with the food and biomass demand of an increased population, while minimizing the impacts of crop production, is therefore a massive upcoming challenge. In this context, we developed four strategies to deliver the biotic output for feeding mankind in 2050. Expansion on suitable and intensification of existing areas are compared to assess associated environmental impacts, including irrigation demand, water stress under climate change, and the productivity of the occupied land. Based on the agricultural production pattern and impacts of the strategies we identified the trade-offs between land and water use. Intensification in regions currently under deficit irrigation can increase agricultural output by up to 30%. However, intensified crop production causes enormous water stress in many locations and might not be a viable solution. Furthermore, intensification alone will not be able to meet future food demand: additionally, a reduction of waste by 50% along the food supply chain or expansion of agricultural land is required for satisfying current per-capita meat and bioenergy consumption. Suitable areas for such expansion are mainly located in Africa, followed by South America. The increased land stress is of smaller concern than the water stress modeled for the intensification case. Therefore, a combination of waste reduction with expansion on suitable pastures generally results as the best option, along with some intensification on selected areas. Our results suggested that minimizing environmental impacts requires fundamental changes in agricultural systems and international cooperation, by producing crops where it is most environmentally efficient and not where it is closest to demand or cheapest.

Characterization factors for thermal pollution in freshwater aquatic environments

To date the impact of thermal emissions has not been addressed in life cycle assessment despite the narrow thermal tolerance of most aquatic species. A method to derive characterization factors for the impact of cooling water discharges on aquatic ecosystems was developed which uses space and time explicit integration of fate and effects of water temperature changes. The fate factor is calculated with a 1-dimensional steady-state model and reflects the residence time of heat emissions in the river. The effect factor specifies the loss of species diversity per unit of temperature increase and is based on a species sensitivity distribution of temperature tolerance intervals for various aquatic species. As an example, time explicit characterization factors were calculated for the cooling water discharge of a nuclear power plant in Switzerland, quantifying the impact on aquatic ecosystems of the rivers Aare and Rhine. The relative importance of the impact of these cooling water discharges was compared with other impacts in life cycle assessment. We found that thermal emissions are relevant for aquatic ecosystems compared to other stressors, such as chemicals and nutrients. For the case of nuclear electricity investigated, thermal emissions contribute between 3% and over 90% to Ecosystem Quality damage.

The water "shoesize" vs. footprint of bioenergy.

Gerbens-Leenes et al. (1) quantify water use of the most relevant global bioenergy crops except palm oil. This is a welcome addition to the existing literature, which often only focuses on “carbon footprints.” Although carbon footprints have been shown to capture a large portion of overall environmental effects for many products and services, the agricultural sector needs additional consideration of other environmental indicators (2). In particular, land use and water consumption can be of substantial importance. Calculating a water footprint is therefore crucial for agriculture-based products.