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.

Multifunctional crops can simultaneously contribute to multiple societal objectives. As a result, they represent an attractive means for improving rural livelihoods. Moringa oleifera is an example of a multifunctional crop that produces nutritious leaves with uses as food, fodder, and a biostimulant to enhance crop growth. It yields seeds containing a water purifying coagulant and oil with cosmetic uses and possible biofuel feedstock. Despite Moringa oleifera's (and other multifunctional crops') various Food-Energy-Water uses, optimizing the benefits of its multiple uses and livelihood improvements remains challenging. There is a need for holistic approaches capable of assessing the multifunctionality of agriculture and livelihood impacts. Therefore, this paper critically evaluates Moringa oleifera's Food-Energy-Water-Livelihood nexus applications to gain insight into the tradeoffs and synergies among its various applications using a systems thinking approach. A systems approach is proposed as a holistic thinking framework that can help navigate the complexity of a crop's multifunctionality. The “Success to the Successful” systems archetype was adopted to capture the competition between the need for leaf yields and seed yields. In areas where there is energy and water insecurity, Moringa oleifera seed production is recommended for its potential to coproduce oil, the water purifying coagulant, and a residue that can be applied as a fertilizer. In areas where food insecurity is an issue, focusing on leaf production would be beneficial due to its significance in augmenting food for human consumption, animal feed, and its use as a biostimulant to increase crop yields. A causal loop diagram was found to effectively map the interconnections among the various uses of Moringa oleifera and associated livelihood improvements. This framework provides stakeholders with a conceptual decision-making tool that can help maximize positive livelihood outcomes. This approach can also be applied for improved management of other multifunctional crops.

Water is a basic resource for food and fuelwood production. In general, people in rural areas of India consume carbohydrate rich staples with small amounts of animal foods. They mostly depend upon fuelwood for cooking. This study assesses the WFs for food and fuel consumption in rural India. The research question is: What is the green, blue and grey water footprint (WF) of food and cooking fuel consumption per province in rural India (m³/cap/year). It used the WF method for the quantification. Data on food and fuelwood consumption were derived from the National Sample Survey (2011–12). Foods were categorized into 6 groups: 1. Rice; 2. Wheat; 3. Oils and fats; 4. Milk; 5. Other animal foods; and 6. Others. Cooking fuel includes: 1. Fuelwood; 2. Kerosene and 3. LPG. Data related to WFs of food were derived from literature reviews and in case of fuelwood, the WFs were calculated for all the provinces of India. Finally, the total WF of per capita consumption is calculated by adding the WF of food and fuelwood. The result shows that there is a large variation in the green, blue and grey WFs for food consumption across the provinces of India. The average WF for food consumption is about 800 m³/cap/year and for fuelwood is 1630 m³/cap/year. Rice and wheat dominate the green, blue and grey WFs for food, with variations among the provinces. The green WF of rice is larger than the green WF of wheat, while wheat has a larger blue WF. For cooking fuel, the average WF of fuelwood is much larger than the WF of fossil based cooking fuels. The total WF for fuelwood is twice the WF for food, showing that in rural areas of developing countries, fuelwood is water intensive with large impact on freshwater resources. Future prospects of increasing consumption of animal products will increase WFs. However, if also cooking fuel is considered, switching to fossil cooking fuel lowers WFs far more and compensates the increase due to larger animal food consumption. The trends for cooking fuel found in India might also be relevant for other developing countries.

Security of the Water-Energy-Food Nexus has become a global concern, threatened by the rapid urbanization, unsustainable consumption of resources, population growth and climate change that exert pressure on resources to meet the socioeconomic demands. Water-Energy-Food Nexus is central for sustainable development and promoting efficient management of resources. Nevertheless, an efficient and sustainable Water-Energy-Food Nexus design requires the participation of multiple stakeholders in the decision-making process. This work presents a multi-objective optimization model for the design of a Water-Energy-Food system that involves the sustainable production of water, energy and food in areas that share economic activities through the industrial, agriculture and livestock sectors. Additionally, a multi-stakeholder assessment is presented to generate a set of solutions, where different priorities are given to the stakeholders. This approach allows quantifying the level of satisfaction of each of the stakeholders. Integration of resources is addressed according to economic and environmental objectives, such as the minimization of the cost of the system, water abstraction and greenhouse gas emissions. As case study, a region located in Mexico was selected based on its industrial activity and the challenges it currently faces in meeting resource demands due to low water availability. Results show that water reuse is crucial to improve the Water-Energy-Food Nexus sustainability. Also, it was found that the most affected sector for water scarcity is the agricultural sector. This model can be the basis for planning the Water-Energy-Food Nexus at regional level involving different stakeholders and for determining sustainable interactions between resources.

The widening gap between China's urban and rural diets and population size poses new challenges to the sustainable supply of agricultural water, undoubtedly increasing the uncertainty of ensuring China's food security. This study compares water required for food in urban and rural areas from 1981 to 2016 using data collected from multiple sources and projects the water required amount in urban and rural areas based different diet scenarios. The results show that food consumption patterns in both urban and rural areas gradually changed from a vegetable-dominated diet to an animal-dominated one in past decades. During 1981–2016, total agricultural water requirements (AWR) for urban residents increased from 167 to 671 billion m³, whereas the for rural residents decreased from 485 to 403 billion m³ at the same period. The urban and rural irrigation water requirements (IWR) shows similar trend to AWR, and increased animal products consumption and decreased grain consumption are the main reason for IWR change in urban and rural areas, respectively. Furthermore, under current dietary patterns, national IWR will reach to 249 billion m³ when the expected population peak occurs (in 2032). However, if according to the recommended diet, China needs to consume 24–41 billion m³ more irrigation water to meet national food demand, and this value will exceed the upper limit allowed by China’s water policy. This study also proposes some measures to ensure China's agricultural water security based on presented findings.

The water-energy-food nexus approach, where closely-connected water, energy and food sectors and their interlinkages are considered together, can be useful to fully understand and address impediments to these sectors’ security and their sustainable development. This study is a review of the current status of the water-energy-food nexus in India, main interlinkages and main challenges to the sustainable development of the nexus. One of the main interlinkages is irrigation in the water-food connection, as the majority of water withdrawn in India is used for agriculture. The water-energy interlinkages are crucial not only in the context of hydropower generation, but also due to the large amounts of water being used for cooling of fossil fuel and nuclear power plants. The pressure on water resources is exacerbated by rainfall reductions in India caused by climate change. Social and economic factors, such as population growth, change in food habits, economic growth and technological advances, further increase the demand for water, energy and food. This all poses significant challenges related to water availability and, as a result, water, food and energy security in India.

In Vietnam, agricultural practices such as fertilizer and pesticide use affect the landscape as well as the availability and safety of food. For instance, pesticides and fertilizer end up in surface water used for drinking water, crop irrigation, and in fish tanks. However, the link to actual food consumption and health is complex and information is lacking. This study considers potential water-related exposure to toxic hazards in northern Vietnam food systems, through the consumption of food commodities and of water. Water pollution is operationalized by considering the following two channels: i) pesticide and nutrient leaching to surface water (share of surface water) and ii) industrial runoff from facilities located in urban areas (share of urban areas). We explore how potential exposure to toxic hazard is related to food consumption choices. Using a sample of the Vietnam Household Living Standard Survey (VHLSS) for 2014, we estimate how shares of food consumption categories in total food consumption are affected by household and landscape characteristics, the latter also reflecting potential environmental pressures. In districts with higher shares of surface water, the share of fish consumption is higher and the share of meat consumption is lower. From an environmental and health perspective, households in water-rich areas thus may have a higher probability of being exposed to toxic chemicals due to higher fish consumption. In districts with higher shares of urban areas, the shares of meat and cereals in total food consumption value were lower, and the shares of fish and fruit and vegetables were higher. The results indicate that food consumption is affected by landscape characteristics that may also influence the level of exposure to water-related environmental pressures, and that this combined effect may potentially exacerbate food safety and health risks. The actual impact is more complex and should be analyzed with more sophisticated data and methods.

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.

In pursuit of continuous economic development, Bangladesh has undertaken long-term plans to boost its productivity in the agriculture, energy, and industrial sectors and to align with the United Nations Sustainable Development Goals (SDGs). Unless these strong interconnections and cross sectoral impacts are recognized, achievement of the future policy goals and national priorities of the concerned ministries regarding food self-sufficiency, cleaner energy sources, and water availability will be compromised. This study focuses on evaluating the impacts of cross-sectoral policy decisions on the interconnected resource systems at a national scale in Bangladesh. A quantitative analysis is performed to identify resource requirements, synergies, and trade-offs related to a set of future strategies. The analysis concludes by showing that land is the most limiting resource for future expansion and that fresh water will become a critical resource if alternative sources of water are not explored, and, that energy generation, if coal and other fossil fuels are favored over alternative energy sources, will significantly add to the total carbon emissions. Given the limitations of land available for agricultural expansion, of renewable water resources, and the challenges in meeting increasing water, energy, and food demands, the strong interdependencies among the interconnected resource systems must be accounted for. The SDG and national priority indicators are found to improve under scenarios for which resources are conserved via alternative sources.

As an illustration of the usefulness of the concept of water-agro-food systems, this paper describes the mechanisms behind the nitrogen cascade from agricultural soils to the coastal sea rivers through aquifers, riparian wetlands, rivers and streams and the estuary, for the case study of the Seine river watershed and its receiving coastal sea. It is stressed that the structure of the agro-food system, i.e. the way food production and trade, as well as consumption and waste management are organized, is the main determinant of the quality of ground- and surface water as well as of aquatic ecosystem functioning.