Green and blue infrastructure (GBI) is defined as a network of landscape components, which include green areas and water bodies. Such an infrastructure, available within an urban space, provides diverse environmental, economic, and social benefits to people and other living organisms.
Concerning the flow of key resources for human survival, food, energy, and water can be interrelated with green and blue infrastructure (GBI). This green-blue system can perform various functions, having the potential to produce multiple services, such as food, water purification, temperature regulation, and others, which are crucial for urban adaptability . Several developed countries implemented their GBI to reduce the urban heat effects (Germany, Australia), improve carbon storage (South Africa), control surface runoff (Brazil, Netherland, USA), and increase local food production (Singapore) .
From a human perspective, in parallel to ecosystem services (ES), GBI can also produce some dis-services . For example, while the cultivation of vegetables generates food to support humans, it might require a huge amount of water. For instance, 200 L of water is required to produce 1 kg of vegetables . Trees in the urban environment provide regulating service, by cooling or shading effects in Summer and protection against the chilled wind in Winter . Nonetheless, trees might need water in abundance . On the other hand, the cultivation of fruit trees, with known edibles such as apples ( Malus spp.), cherries ( Prunus spp.), and pears ( Pyrus spp.), is prohibited in urban streets due to the falling of their fruits on footpath and stroller injuries . Green roofs (GRs) are capable of reducing the fluctuation of indoor temperatures in cold as well as warm weather conditions and minimizing the energy consumption of buildings . Sometimes, the conservation of energy utilization can be induced, due to unexpected natural factors (e.g., the rainfall will reduce the requirements of extra water) . Moreover, GRs reduce stormwater runoffs , which may include heavy metals such as Fe, Zn, Cu, and Al . According to the authors’ observations, large amounts of metals can be upheld (92% of Cd, 99% of Pb, 97% of Cu, and 96% of Zn), especially in summer. However, such heavy metals might contaminate the vegetables .
Food, energy and water (FEW) are key inter-linked resources for the survival of individuals and human communities . Such a mutual relation among different resources and their dynamics is synthesized through the nexus concept and framework . For instance, energy is necessary for food production, landfill gas, and waste from food production and consumption can be used for energy generation . Food production and consumption also use water and generate wastewater . Energy is needed for water treatment processes, while energy production requires water and generates wastewater .
However, FEW nexus should be further integrated with ecosystem . In fact, this integration would support the achievement of sustainable development goals . GBI can act as a unifying spatial and functional (referred to provide ecosystem services) framework, as well as a system within which flows of food, energy, and water exist and can be quantified. Figure 1 illustrates the nexus structure. The food production practices drive energy use intensities and water extraction rates. At the same time, energy is essential for food and water, and water safety is the key to electricity generation and food production. Water is demanded to produce electricity, e.g., hydropower, and the harvesting of biomass can be used for biofuel production. Birol and Das  reported that around 15% of global water extraction was consumed for the production of energy. Energy is essential for the transport, pumping, and treatment of portable and non-portable water, i.e., wastewater, for human utilization or vegetation irrigation. On the contrary, approximately 8% of energy is used for water purposes worldly . Regarding power generation integration in the water cycle, some of the GBI, e.g., constructed wetlands, can provide opportunities to mitigate energy consumption, for instance, it generates humus as well as nutrient-rich effluent water that can be utilized directly to irrigate energy crops and for short rotation vegetation through fertigation process . Moreover, the treated water can be used for flush toilets, street vegetation, and washing the roads, and also to reduce the extra energy burden that is required for wastewater treatment. This is why a “GBI–FEW” nexus can be considered in the study of urban metabolism, with the purpose of a better management of resources, supporting the transition to more sustainable energy systems.
Figure 1. The sustainable “GBI-FEWN” management framework in an urban settlement.
|Direct ES||Indirect ES||Edis||Direct ES||Indirect ES||Edis||Direct ES||Indirect ES||Edis|
|Providing Food||Providing Shrubs, Grasses and Flowers||Risk of Food Contaminated by Heavy Metal & Pollutants||Reduce Stormwater Runoff||Enhanced Water Quality||Increase Available Water Supply||Groundwater Recharge||Reduced Water Treatment Needs||Increasing Water Consumption||Water Pollution from Fertilizer & Chemicals||Reduce Energy Usage||Providing Wood and Other Bio-Waste||Reduced Urban Heat Island Effect||Reduction of Carbon Footprints||Increasing Energy Consumption||LCA/LCC Model||i-Tree Model||Field Surveys or Statistical Analysis||No. of Publication|
The interactive flows in the energy, water, and food system as a food–energy–water (FEW) nexus are very important for the sustainable development of cities, and they can be arbitrated via green-blue infrastructure (GBI) in the built-up area. Here, our focus is on non-built “nature in cities” infrastructure. The GBI generates multiple ecological benefits (food production, water and energy-saving, and microclimate regulation) in urban centers. The FEW flows also generate some negative effects (dis-services) within the GBI, for example, food products within the green-blue system, but over-application of pesticides and fertilizers, could generate a release of toxic substances, that might also improve water quality. If water is extracted to produce energy, it might reduce the natural water flows of rivers, impacting on the biosphere too. Well-planned urban construction can help to control the negative effects.There is a need to make integrative and deliberate policy to link the GBI with each element in the urban FEW nexus. We also focus on nexus modeling techniques in terms of their benefits, drawbacks, and applications. Moreover, guidance is provided on the choice of an adequate modeling approach. Finally, water, energy, and food are linked physically, but tradeoffs among them often increase when their management is put into practice. We must minimize the tradeoffs and build up synergies between food, energy, and water by using a holistic approach. Therefore, the GBI-FEW nexus has become a major approach to address the relation between three important individual resource components of sustainability.