The water footprint of Milan

Evaluation of the influence on water consumption and water scarcity of different healthy diet scenarios

A deep understanding of the water-food nexus it is of a paramount importance as an avenue for sustainable development. Water forms the foundation for food production and a sustainable use of this resource is essential to guarantee the long-term productivity and to build resilient capacity in food and agricultural systems. Here we present methodological challenges regarding different water footprint (WF) methods applied to different dietary scenarios. The volumetric WF of three theoretical but realistic dietary patterns has been quantified (Omnivorous(O), Vegetarian(V) and Vegan(VG)), by means of the Water Footprint Network methodology. Moreover, the AWARE methodology is applied to assess potential impacts of water use trough the Water Scarcity Footprint (WSF). Diets are set to integrate and consider different drivers for food consumption encompassing the social value of the Mediterranean diet, healthy diet recommendations, food preferences of Italian consumers and the trade dimension of foodstuffs. In terms of volumetric WF, the O diet is the most water intensive one accounting for 2800 L/capita/day. A shift from an O to a V and VG diets allows to reduce the volumetric WF respectively 10% and 14%. Green water consumption accounts for the largest share (85%) in all three scenarios. Considering the WSF, V healthy diet is similar to the VG resulting in 11,069 and 11,130 L H₂Oeq/capita/day respectively, whereas the O diet resulted in 11,932 L H₂Oeq/capita/day. A sensitivity analysis was performed by changing each food category, one at a time, to its maximum and minimum value, in order to evaluate the significance of changes in the volumetric WF and WSF as well as the variables that mostly contribute to them. Results show that the volumetric WF associated with V and VG diets consumption overlay the O diet in respectively 53.5% and 35.7% of runs, while overlapping is improved comparing WSFs results. In this case, the WSFs of V and VG diets overlay the O diet in 83.5% of runs, suggesting that the alternative dietary scenarios would have little effect on the overall WSF and that the results are particularly sensitive to the different countries of importation. Results demonstrate the need to consider both volumetric WF and WSF with particular attention to trade analysis in order to support the development of new policies with the aim to foster sustainable consumption patterns, while preserving water resources.

Is the Water System Healthy in Urban Agglomerations? A Perspective from the Water Metabolism Network

Urban agglomerations are a primary spatial focus of socioeconomic activity and inherently include large volumes of embodied water. We have applied the concept of water metabolism health to comprehensively evaluate the overall operation of water systems in urban agglomerations and propose an innovative assessment framework. In particular, we constructed a water metabolism network (WMN) model to simulate a water system in which different cities and sectors are integrated, combining a newly compiled multiregional input-output (MRIO) table of water flow with ecological network analysis (ENA). A case study considering the Pearl River Delta (PRD) urban agglomeration in 2015 demonstrates that its network is well synergic but highly dependent, with considerable negative effects. Highly developed cities in southeastern of the PRD exhibit higher embodied water productivity and robustness but impose considerable negative effects on the water system. We found the agricultural sector to be a dominant controller of the network; the construction and service sectors represent the primary beneficiaries with strong competition. We suggest measures at various scales to improve water utilization efficiency and promote positive interactions between components, thus improving water metabolism system health for urban agglomerations.

Water Resources for Sustainable Healthy Diets: State of the Art and Outlook

Sustainable healthy diets are high on the research and policy agendas. One of the crucial resources to provide such diets are water resources. This paper provides a brief overview of the current research state regarding this topic, with a focus on the water footprint concept, as latter quantifies water use along a supply chain. The water footprint (WF) quantifies blue and green water consumption, as both these water resources are essential for food and energy production as well as for the environment. Different kinds of information are embedded in a dietary WF and different data sources and modelling approaches exist, leading to WF dietary amounts that are not always directly comparable. A full sustainability assessment of a dietary WF encompasses three components: (1) an equity assessment of the total WF amount; (2) an efficiency assessment for each food item in the diet as well as (3) an impact assessment (blue water stress and green water scarcity) for each food item in the diet. The paper concludes with an outlook on future research on the topic, listing the following points: (1) future clarity in system boundary and modelling assumptions, with comparison of results between different approaches; (2) full sustainability assessments including all three components; (3) dietary footprint family assessments with the WF as one member; (4) WF assessments for multiple dietary regimes with support to the development of local dietary guidelines and (5) assessment of the synergies with LCA-based mid-point (scarcity-weighted WF) and end-point (especially human health) indicators and evaluation of the validity and empirical significance of these two indicators

The Water Footprint of Diets: A Global Systematic Review and Meta-analysis

Agricultural water requirements differ between foods. Population-level dietary preferences are therefore a major determinant of agricultural water use. The "water footprint" (WF) represents the volume of water consumed in the production of food items, separated by water source; blue WF represents ground and surface water use, and green WF represents rain water use. We systematically searched for published studies using the WF to assess the water use of diets. We used the available evidence to quantify the WF of diets in different countries, and grouped diets in patterns according to study definition. "Average" patterns equated to those currently consumed, whereas "healthy" patterns included those recommended in national dietary guidelines. We searched 7 online databases and identified 41 eligible studies that reported the dietary green WF, blue WF, or total WF (green plus blue) (1964 estimates for 176 countries). The available evidence suggests that, on average, European (170 estimates) and Oceanian (18 estimates) dietary patterns have the highest green WFs (median per capita: 2999 L/d and 2924 L/d, respectively), whereas Asian dietary patterns (98 estimates) have the highest blue WFs (median: 382 L/d per capita). Foods of animal origin are major contributors to the green WFs of diets, whereas cereals, fruits, nuts, and oils are major contributors to the blue WF of diets. "Healthy" dietary patterns (425 estimates) had green WFs that were 5.9% (95% CI: -7.7, -4.0) lower than those of "average" dietary patterns, but they did not differ in their blue WFs. Our review suggests that changes toward healthier diets could reduce total water use of agriculture, but would not affect blue water use. Rapid dietary change and increasing water security concerns underscore the need for a better understanding of the amount and type of water used in food production to make informed policy decisions.

Cities as hotspots of indirect water consumption: The case study of Hong Kong

During the last years, the city of Hong Kong has made large investments to make its urban water supply system more water efficient and sustainable. As such, its municipal water abstraction - often defined as direct water use - has decreased from 355 litre per capita per day (l/cap/d) in 2005 to 326 l/cap/d in 2013. Due to its political history, Hong Kong is unique in the world in data availability on urban food consumption. It is therefore the ideal case study to show typical urban food consumption behaviour and its related indirect water use. The objective of this paper is to show the large water quantities associated with indirect water use and that the citizens of Hong Kong can additionally save much more water by looking at this indirect water use. The current average diet in Hong Kong is very different to the average Chinese diet. It is characterised by a high intake of water intensive products like animal products and sugar, leading to a food related indirect water use or water footprint (WF_cons) of 4727 l/cap/d. According to recommendations from the Chinese Nutrition Society for a healthy diet, the intake of some product groups should be increased (vegetables and fruit) and of other product groups reduced (sugar, crop oils, meat and animal fats). This would result in a reduction of the WF_cons of 40% to 2852 l/cap/d. Especially the reduced intake of meat (including offals) from currently 126 kg per capita per year (kg/cap/yr) to the recommended value 27 kg/cap/yrwould results in a substantial WF_cons reduction. Meat consumption in Hong Kong is extremely high. A pesco-vegetarian diet would result in a reduction of 49% (to 2398 l/cap/d) and a vegetarian diet in a 53% (to 2224 l/cap/d) reduction. Hong Kong citizens can thus save a lot of water through a change in their diet. Many of the products consumed, contribute to different levels of blue water scarcity in the regions of origin Hong Kong imports from. This poses a water-related risk to food security in Hong Kong. As all diet scenarios also result in a lower blue WF_cons, they decrease this risk. In order to become sustainable, (mega)cities should reduce their dependency on distant resources and ecosystems.

Large cities get more for less: Water footprint efficiency across the US

Many urban indicators and functional citywide properties have been shown to scale with population due to agglomeration effects. We hypothesize that scaling relations may also exist for water-related urban indicators such as the water footprint. The water footprint is an indicator of water use that measures humans' appropriation of freshwater resources. We analyze the scaling of the water footprint for 65 mid- to large-sized US cities using both empirical estimates and a social interaction network model of city functioning. The network model is used to explain the presence of any scaling exponent in the empirical estimates of the urban water footprint by linking to previous theories of urban scaling. We find that the urban water footprint tends to approximately show sublinear scaling behavior with both population and gross domestic product. Thus, large cities tend to be more water footprint efficient and productive than mid-sized cities, where efficiency and productivity are quantified, in a broad sense, as deviations from a linear scaling exponent. We find the sublinear scaling may be linked to changes in urban economic structure with city size, which lead to large cities shifting water intensive economic activities to less populated regions. In addition, we find that green water contributes to the scaling both positively by transferring the dependence of food consumption on population into the water footprint and negatively by increasing heterogeneity. Overall, the proposed scaling relations allow for the comparison of water footprint efficiency and productivity of cities. Comparing these properties and identifying deviations from the expected behavior has implications for water resources and urban sustainability.

Internal (blue) water footprint of municipal consumption: a case study for Turkey

This study aimed to develop a common approach to investigate (blue) water footprint of consumption of municipalities. Analysis framework consists of two distinct phases as: water abstraction profile and water distribution and water use profile. In the proposed approach municipal water footprint (WF_municipal) comprises three components: domestic water footprint (WF_domestic), industrial/commercial water footprint (WF_{industrial/commercial}), and public water footprint (WF_public). The application of the methodology was demonstrated in Turkey. The overall objective was to identify water consumption profile regarding model components and assess spatial and temporal distributions in the country scale. In this scope, each component was determined for 81 cities. After the investigation of spatial differences, an answer to the question of, "whether water use is increasing or decreasing over time" was found. Results investigated that WF_municipal was 140 L/ca.day in average and reached up to 300 L/ca.day in some cities. WF_domestic was about 100 L/ca.day and cities having lower values mostly located on north-west, south-east of the country. Furthermore, few spots with high values were observed for WF_{industrial/commercial} (with 10 L/ca.day average), and relatively lower values belonged to the cities in south-eastern region. WF_public having 30 L/ca.day mean value had extremes in eastern part. Based on water consumption characteristics, cities were grouped using factor analysis and results created four groups of cities. Although eastern and western cities had no trends in water abstraction rate, other regions had decreasing trend in last 20 years. Investigation of (blue) water footprint of consumption of municipalities is believed to assist water managers to identify water use profiles and assess spatial and temporal distributions. This is important because water resources are becoming increasingly stretched to accommodate continued population and economic growth and to restore environmental flows.

Physical water scarcity metrics for monitoring progress towards SDG target 6.4: An evaluation of indicator 6.4.2 "Level of water stress"

Target 6.4 of the recently adopted Sustainable Development Goals (SDGs) deals with the reduction of water scarcity. To monitor progress towards this target, two indicators are used: Indicator 6.4.1 measuring water use efficiency and 6.4.2 measuring the level of water stress (WS). This paper aims to identify whether the currently proposed indicator 6.4.2 considers the different elements that need to be accounted for in a WS indicator. WS indicators compare water use with water availability. We identify seven essential elements: 1) both gross and net water abstraction (or withdrawal) provide important information to understand WS; 2) WS indicators need to incorporate environmental flow requirements (EFR); 3) temporal and 4) spatial disaggregation is required in a WS assessment; 5) both renewable surface water and groundwater resources, including their interaction, need to be accounted for as renewable water availability; 6) alternative available water resources need to be accounted for as well, like fossil groundwater and desalinated water; 7) WS indicators need to account for water storage in reservoirs, water recycling and managed aquifer recharge. Indicator 6.4.2 considers many of these elements, but there is need for improvement. It is recommended that WS is measured based on net abstraction as well, in addition to currently only measuring WS based on gross abstraction. It does incorporate EFR. Temporal and spatial disaggregation is indeed defined as a goal in more advanced monitoring levels, in which it is also called for a differentiation between surface and groundwater resources. However, regarding element 6 and 7 there are some shortcomings for which we provide recommendations. In addition, indicator 6.4.2 is only one indicator, which monitors blue WS, but does not give information on green or green-blue water scarcity or on water quality. Within the SDG indicator framework, some of these topics are covered with other indicators.

What Is the Contribution of City-Scale Actions to the Overall Food System's Environmental Impacts?: Assessing Water, Greenhouse Gas, and Land Impacts of Future Urban Food Scenarios

This paper develops a methodology for individual cities to use to analyze the in- and trans-boundary water, greenhouse gas (GHG), and land impacts of city-scale food system actions. Applied to Delhi, India, the analysis demonstrates that city-scale action can rival typical food policy interventions that occur at larger scales, although no single city-scale action can rival in all three environmental impacts. In particular, improved food-waste management within the city (7% system-wide GHG reduction) matches the GHG impact of preconsumer trans-boundary food waste reduction. The systems approach is particularly useful in illustrating key trade-offs and co-benefits. For instance, multiple diet shifts that can reduce GHG emissions have trade-offs that increase water and land impacts. Vertical farming technology (VFT) with current applications for fruits and vegetables can provide modest system-wide water (4%) and land reductions (3%), although implementation within the city itself may raise questions of constraints in water-stressed cities, with such a shift in Delhi increasing community-wide direct water use by 16%. Improving the nutrition status for the bottom 50% of the population to the median diet is accompanied by proportionally smaller increases of water, GHG, and land impacts (4%, 9%, and 8%, systemwide): increases that can be offset through simultaneous city-scale actions, e.g., improved food-waste management and VFT.

Water consumption related to different diets in Mediterranean cities

Providing the sustainable development goals (SDGs) water, food and energy security to cities relies strongly on resource use outside city borders. Many modern cities have recently invested in a sustainable urban water system, and score high in international city rankings regarding water management and direct urban water use. However, these rankings generally neglect external resource use for cities. Here we quantify the water resources related to food consumption in thirteen cities located in Mediterranean countries, by means of the water footprint (WF) concept. These WFs amount from 3277l per capita per day (l/cap/d) to 5789l/cap/d. These amounts are about thirty times higher than their direct urban water use. We additionally analyse the WF of three diet scenarios, based upon a Mediterranean dietary pattern. Many authors identify the Mediterranean diet as cultural heritage, being beneficial for human health and a model for a sustainable food system. The first diet scenario, a healthy Mediterranean diet including meat, leads to WF reductions of -19% to -43%. The second diet scenario (pesco-vegetarian), leads to WF reductions of -28% to -52%. The third diet scenario (vegetarian), leads to WF reductions of -30% to -53%. In other words, if urban citizens want to save water, they need to look at their diets.