Emerging challenges and opportunities for the food–energy–water nexus in urban systems

Food-Energy-Water Nexus in compliance with Sustainable Development Goals for integrating and managing the core environmental verticals for sustainable energy and circular economy

Food, energy, and water resources are intricately interconnected, and nexus provides a holistic approach for addressing these complex links to minimize inefficiencies and waste. Nexus approach and circular economy are considered as effective solutions for sustainability. Quantification of these relations is the first step towards incorporating nexus modeling which helps sustainable production and consumption. For achieving the Sustainable Development Goals, understanding and effectively managing the FEW nexus becomes imperative. With an integral performance perspective, there is a need to address the interdependencies and trade-offs among food, energy, and water systems and challenges of economic, social and environmental sustainability. The aim of this study is to provide a comprehensive analysis of the FEW nexus, identify key opportunities and challenges, and propose integrated strategies for managing these core environmental verticals sustainably. The study addresses the accomplishment of these goals through nexus approaches and outlines the need for technological advancements for shared benefits among resources, contributing to conceptual development of nexus and circular economy. The results highlight the critical importance of adopting a nexus approach to advance sustainable development goals, enhance resource efficiency, and promote synergistic solutions across food, energy, and water systems.

Food-energy-water nexus optimization brings substantial reduction of urban resource consumption and greenhouse gas emissions

Urban sustainability is a key to achieving the UN sustainable development goals (SDGs). Secure and efficient provision of food, energy, and water (FEW) resources is a critical strategy for urban sustainability. While there has been extensive discussion on the positive effects of the FEW nexus on resource efficiency and climate impacts, measuring the extent to which such synergy can benefit urban sustainability remains challenging. Here, we have developed a systematic and integrated optimization framework to explore the potential of the FEW nexus in reducing urban resource demand and greenhouse gas (GHG) emissions. Demonstrated using the Metropolis Beijing, we have identified that the optimized FEW nexus can reduce resource consumption and GHG emissions by 21.0 and 29.1%, respectively. These reductions come with increased costs compared to the siloed FEW management, but it still achieved a 16.8% reduction in economic cost compared to the business-as-usual scenario. These findings underscore the significant potential of FEW nexus management in enhancing urban resource efficiency and addressing climate impacts, while also identifying strategies to address trade-offs and increase synergies.

Identifying the drivers of changes in embodied food-energy-water in the Bohai mega-urban region, China: A perspective of final demands

Food-energy-water (FEW) systems in the Bohai mega-urban region (MUR) have experienced astonishing changes in recent decades; however, the dynamics of these changes are not fully understood. This study combined an ecological multiscale input-output model and a structural decomposition analysis (SDA) to explore the variation in embodied FEW consumption and its drivers. The results showed that, although almost all sectoral embodied FEW intensities decreased, embodied FEW demands increased by approximately 9.9×10⁸ tons, 4.61×10⁷ TJ and 1.1×10¹¹ m³ over 10-year period. The embodied FEW flow diagrams show that local consumption and trade were strengthened. Urban household consumption, fixed capital formation and exports were the main components affecting the embodied FEW use increases. An SDA revealed that the consumption level effect (∆c) was the dominant contributor that promoted the increase in the Bohai MUR's embodied FEW consumption. The scale effect (∆p) also had a positive effect on the embodied FEW consumption increases. The technological effect (∆e) was the primary contributor to offset the embodied FEW consumption increase. The economic efficiency effect (∆L) and structural effect (∆s_d) also contributed to offsetting the total embodied FEW consumption increase. The effect of the change in domestic and foreign imports (∆D and ∆F) impacted the increase in embodied FEW mainly through the change in the embodied FEW intensities and trade volumes. This study identified the changes in FEW systems and highlighted future coping strategies.

How Can Material Stock Studies Assist the Implementation of the Circular Economy in Cities?

City and regional planners have recently started exploring a circular approach to urban development. Meanwhile, industrial ecologists have been designing and refining methodologies to quantify and locate material flows and stocks within systems. This Perspective explores to which extent material stock studies can contribute to urban circularity, focusing on the built environment. We conducted a critical literature review of material stock studies that claim they contribute to circular cities. We classified each article according to a matrix we developed leveraging existing circular built environment frameworks of urban planning, architecture, and civil engineering and included the terminology of material stock studies. We found that, out of 271 studies, only 132 provided information that could be relevant to the implementation of circular cities, albeit to vastly different degrees of effectiveness. Of these 132, only 26 reported their results in a spatially explicit manner, which is fundamental to the effective actuation of circular city strategies. We argue that future research should strive to provide spatial data, avoid being siloed, and increase engagement with other sociopolitical fields to address the different needs of the relevant stakeholders for urban circularity.

A systematic approach for assessing water, energy and food security during the COVID-19 pandemic: case study of Mexico

Assessing the security of the water-energy-food nexus is a topic of great importance, which allows determining the situation of each resource to implement actions for sustainable management of these resources in today's society. For this reason, a systematic procedure is proposed to evaluate the synergies of the water-energy-food nexus in a large region that is divided into subregions that allow considering their interactions. The new procedure considers the availability, accessibility and regional interdependence of resources while annexing economic and social aspects. A composite index called the WEF Global Index is developed, which involves the WEF nexus index and has nine indicators that evaluate the availability, accessibility and regional interdependence of each resource in the water-energy-food nexus. This new index considers the Gross Domestic Product per capita and the involved population. As a case study, the 32 states of Mexico were considered to assess the effects of the COVID-19 pandemic on the economy and the security of the water-energy-food nexus at the state level. For this, the composite index was evaluated in the years 2019 and 2020. The results show that from 2019 to 2020, the value of the global index increased in 13 states, in 21 states the security index of the WEF nexus increased, and in 9 states the GDP per capita index increased. On the other hand, the results indicate that in 11 states there was no improvement in the nexus security index due to the increase in water demand, which considerably affected the water availability indicator.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-022-02671-2.

A system dynamics model to simulate the water-energy-food nexus of resource-based regions: A case study in Daqing City, China

Resource-based regions (RBRs) have made significant contributions to the social and economic development of nations. The long-term and high-intensity development of resources puts tremendous pressure on water, energy and food resources and the ecological environment. Exploring the water-energy-food nexus (WEF nexus, WEFN) of RBRs is key to making informed decisions about regional sustainable development. In this study, a feedback model for the WEFN of RBRs was developed using a system dynamics approach. The WEFN model not only describes the WEFN system from both the supply and demand sides, but also classifies WEF resources. Using Daqing, China, as a case study, five future scenarios were designed to explore the impacts of real policies designed by different government departments on the WEFN system. Comparing the predicted results of a scheme for business as usual, a scheme for developing bioenergy, a scheme for adjustment of the production structure, a scheme for strengthening the development of water and food resources and a scheme for saving WEF resources revealed that the schemes for adjustment of the production structure and for saving WEF resources will not only improve the security of WEF resources, but also reduce pollution of the water environment by human activities, which is conducive to improving the overall benefits of the WEFN system. Finally, some practical suggestions are put forward to promote the coordinated development of the WEFN system. The WEFN model is a multi-centric tool for integrated resources management, and can be expanded to other RBRs and provides scientific support for decision-makers.

Unfolding the synergy and interaction of water-land-food nexus for sustainable resource management: A supernetwork analysis

Given the large amounts of water, land, and food embodied in the trade of goods and services, a key step in decoupling extensive resource consumption from the economic system is to understand the full impact of socioeconomic development on the water-land-food nexus. This study integrates input-output analysis, ecological network analysis, and Dempster-Shafer evidence theory into a supernetwork model to detect the water-land-food nexus among economic sectors with an aim to explore effective strategic paths for resource management and to facilitate the construction of a resource-saving society. Results show that most sectors of China are resource inefficient and that all resource systems are unsustainable as reflected in the low performance of their Finn's cycling index and system robustness. Meanwhile, results of flow networks analysis show an extremely uneven land resource allocation where more than 94% of the land used in China is classified as direct agricultural land. The water-land-food nexus can gain resource saving bonus via enhancing the robustness of economy. However, the co-benefits from the nexus are negligibly small for the resource utilization efficiency. The results also indicate that the relevant resource-saving policies on food and water are highly likely to gain resource co-benefits due to their similarities in sectoral importance. Correspondingly, a set of strategic measures, including adopting a tiered resource price, deepening industrial convergence of agriculture, enhancing agriculture-food nexus, and managing water or land use from the food consumer side, are designed to build a resource-saving society. The findings of this study can provide additional insights into the impacts of the economy on the water-land-food nexus, which is beneficial for achieving an efficient and coordinated management of resources.

Causal Relations of Upscaled Urban Aquaponics and the Food-Water-Energy Nexus—A Berlin Case Study

Aquaponics, the water-reusing production of fish and crops, is taken as an example to investigate the consequences of upscaling a nature-based solution in a circular city. We developed an upscaled-aquaponic scenario for the German metropolis of Berlin, analysed the impacts, and studied the system dynamics. To meet the annual fish, tomato, and lettuce demand of Berlin’s 3.77 million residents would require approximately 370 aquaponic facilities covering a total area of 224 hectares and the use of different combinations of fish and crops: catfish/tomato (56%), catfish/lettuce (13%), and tilapia/tomato (31%). As a predominant effect, in terms of water, aquaponic production would save about 2.0 million m3 of water compared to the baseline. On the supply-side, we identified significant causal link chains concerning the Food-Water-Energy nexus at the aquaponic facility level as well as causal relations of a production relocation to Berlin. On the demand-side, a ‘freshwater pescatarian diet’ is discussed. The new and comprehensive findings at different system levels require further investigations on this topic. Upscaled aquaponics can produce a relevant contribution to Berlin’s sustainability and to implement it, research is needed to find suitable sites for local aquaponics in Berlin, possibly inside buildings, on urban roofscape, or in peri-urban areas.

Measuring urban food-energy-water nexus sustainability: Finding solutions for cities

A city is the place where food, energy, and water consumption happen. This consumption leads to challenges and has a strong impact on natural sources. Although researchers broadly agree on the importance of incorporating the concept of the food, energy, and water nexus into policy strategies and decision-making, the assessment system for how governance methods can improve the provision of these three essential services is relatively blank. To clarify the policy mechanisms and heterogeneity of sustainability issues related to the food, energy and water nexus at the city level, this study develops an indicator system to guide the implementations and optimize urban sustainability. A qualitative approach is employed to form the priority strategies in in four selected cities: Amsterdam, Eindhoven, Taipei, and Tainan. The results show that renewable energy plays an essential role in the food-energy-water nexus. In addition, we also observed that future work should focus on technological innovation. These observations imply that the unique combination of influence factors in food-energy-water sustainability offers a comprehensive outlook of the broad and complex challenges that a city faces due to resource limitations, which can help inform future governance practices. Finally, some policy recommendations are made for highlighting and the activities needed to work. The results of the present evaluation could be used as a tool to strengthen food-energy-water management in the future. They can guide managers to develop possible solutions that ensure resources are applied successfully according to the visions of multiple perspectives and help the relevant ministries to improve future consultation plans.

The nexus of water-energy-food in China's tourism industry

The tourism industry contributes significantly to the growth of the global economy and is considered to be strongly associated with a large amounts of water and energy consumption. In this study, the tourism water footprint (TWF) and the tourism energy footprint (TEF) of 138 sectors were investigated to examine the water-energy-food (W-E-F) nexus in the Chinese tourism industry from 2012 to 2017 by developing the water- and energy-based environmentally extended input-output analysis with the tourism satellite account. This study revealed that the W-E-F supply groups consumed total 15,556 million m³ of water and 4,964 million tce of energy to support the Chinese tourism industry. The largest contributor to the total TWF is the indirect water use from the food supply group (65%), while the largest proportion of total TEF is contributed by the direct energy use from 11 tourism direct sectors (63%), most especially the air transport sector. A much larger growth of the tourism industry was observed in 2017 compared to that of 2012. The structure decomposition analysis revealed that the growth of the overall water and energy consumption of China tourism is mainly driven by the growth of the total tourism expenditure, i.e. the scale effect. It is the same case for the food supply group associated with the Chinese tourism industry. In contrast, the contribution of the changes to the tourism expenditure composition is relatively low. Furthermore, the growth in water and energy consumption can be offset effectively by reducing the water and energy use coefficient and adjusting the economic production structure of tourism and its associated food supply group. In sum, the food supply and air transport sectors play a crucial role in the water-energy-food nexus of the tourism industry. Therefore, in the future, focus should be placed on improving the water and energy use efficiency of these sectors as well as enhancing their production structures.

Role of Smart Cities in Optimizing Water-Energy-Food Nexus: Opportunities in Nagpur, India

The evolving concept of ‘Smart Cities’ (SC) is today gaining global momentum in scientific and policy arenas. With the rising potential for jobs and improved lifestyle, these fast-growing cities are witnessing an ever-increasing concentration of populations and economic activities. However, the core aspect of sustainability is often overshadowed in SC by the components of economic growth. In view of the rising water, energy, and food (collectively referred to as WEF) demands in cities and the interlinkages between WEF systems, this study aims to highlight the role of SC in enhancing WEF resource efficiency from a nexus perspective. To study the current trends of SC developments first, a specific case of proposed Nagpur smart city (India) is reviewed based on document analysis and preliminary discussions with local government officials. Thereafter, bibliometric analysis (based on Scopus data) is conducted to establish a comprehensive understanding of existing SC research in varying domains of interlinked WEF systems. While the proposed Nagpur smart city is observably focused on city-centric goals with a high emphasis on infrastructure development, this study underlines the need for environmental resource conservation at a transboundary level. The key opportunities for optimizing the WEF nexus in Nagpur are then highlighted in reference to the bibliometric analysis.

Optimization of Regional Water-Energy-Food Systems Based on Interval Number Multi-Objective Programming: A Case Study of Ordos, China

Water, energy, and food are the most important basic resources for economic and social development. In the context of global population growth, environmental degradation, and resource shortages, the interrelationship between the water, energy, and food has become increasingly important. In this paper, the city of Ordos in China was selected as a study area. Firstly, this paper sorted out relevant research literature and fully understood the concept of water-energy-food (WEF) nexus. Then, an optimization model of WEF system was constructed based on interval number multi-objective programming, which took the comprehensive coordination deviation degree of the WEF system security and carbon dioxide emission minimization as the target. At the same time, the optimization model was constructed with full consideration of constraints such as economic benefit, water resource consumption, energy production, food production and environmental pollution emission. The results showed that the production of coal, thermal power, hydropower, wind power, and food all show an upward trend. Among them, the production of hydropower has the largest change, and the food production has the smallest change. In terms of water resource utilization, food production has the largest allocation of water resources accounting for nearly 80%, followed by coal production, thermal power generation and hydropower generation. The smallest allocation is natural gas. In particular, the allocation of water for coal production and hydroelectric power generation has increased significantly. Finally, the policy recommendations were put forward to promote the sustainable development of WEF system in Ordos. The optimization research on the WEF system can help to ensure the WEF system security in Ordos and promote the sustainable development of WEF system, which also can provide reference for other regions.

Multi-Objective Optimization of a Regional Water-Energy-Food System Considering Environmental Constraints: A Case Study of Inner Mongolia, China

Water, energy, and food, as the basic material resources of human production and life, play a prominent role in social and economic development. As the imbalance between the supply and demand of water, energy, and food increases, a highly sensitive and fragile relationship gradually forms among water, energy, and food. In this paper, Inner Mongolia in China is selected as a research area. Firstly, synergy theory is applied to establish the framework of a water-energy-food system. Then, a multi-objective programming model is constructed, where the objective functions are defined to minimize the integrated deviation degree and pollutant emissions of the water-energy-food system. Meanwhile, maximization of the water benefit, energy production, and food production is also considered. In addition, the model takes economy, environment, water, energy, and food as constraints. Finally, a genetic algorithm is designed for accurately assessing the most promising results. The results show that the cooperation degree of the water-energy-food system in Inner Mongolia is getting better and better, and the pollutant emission from the water-energy-food system is decreasing. In 2020, the proportion of agricultural water consumption fell by 1%, while that of industrial water consumption rose by 0.48%. The production of coal, natural gas, and power are all showing an increasing trend. Among them, the increase of natural gas production is as high as 38,947,730 tons of standard coal. However, the proportions of coal, natural gas, and power change inconsistently, where the proportions of coal and natural gas increase while that of power decreases. Corn production accounts for more than 80% of the total, which is in the eldest brother position in the food industry structure. Besides, there are differences between the planned values and optimal values of decision variables. Finally, suggestions are put forward to improve the sustainable development of water-energy-food in Inner Mongolia.

Transboundary Environmental Footprints of the Urban Food Supply Chain and Mitigation Strategies

Food supply has been the central issue of human development for millennia and has become increasingly critical in an urbanizing world. However, the environmental footprints and associated mitigation strategies of food consumption have rarely been comprehensively characterized at urban or regional scales. Here, we analyze the water, carbon, reactive nitrogen, and phosphorus footprints of food consumption in Chinese urban regions and demonstrate how such information can help to formulate tailored mitigation strategies. The results show that in three of the largest urban regions of China, 44-93% of the four footprints are embodied in transboundary food supply. The size of the footprints and the effectiveness of mitigation measures in food supply chain vary across the environmental footprints and urban regions. However, targeting agriculture and food processing sectors in Hebei, Shandong, and Henan provinces can reduce these footprints by up to 47%. Our findings show that the analysis of the environmental footprints along the transboundary food supply chains could inform individualized and effective mitigation targets and strategies.

Synergies within the Water-Energy-Food Nexus to Support the Integrated Urban Resources Governance

Rapid urbanization poses great challenges to water-energy-food nexus (WEF-Nexus) system, calling for integrative resources governance to improve the synergies between subsystems that constitute the Nexus. This paper explores the synergies within the WEF-Nexus in Shenzhen city while using the synergetic model. We first identify the order parameters and their causal paths in three subsystems and set several eigenvectors under each parameter. Secondly, a synergetic model is developed to calculate the synergy degree among parameters, and the synergetic networks are then further constructed. Centrality analysis on the synergetic networks reveals that the centralities of food subsystem perform the highest level while the water subsystem at the lowest level. Finally, we put forward some policy implications for cross-sectoral resources governance by embedding the synergy degree into causal paths. The results show that the synergies of the Nexus system in Shenzhen can be maximized by stabilizing water supply, coordinating the energy imports and exports, and reducing the crops sown areas.