Full length articleQuantification of the food-water-energy nexus in urban green and blue infrastructure: A synthesis of the literature
Introduction
Projections suggest that 6.7 billion people, accounting for 67% of Earth's population will reside in urban areas by 2050 and it is estimated that 81% of the urban population will be in countries classified as developed by 2030 (United Nations, 2019). Despite socioeconomic benefits, augmenting urbanization leads to numerous problems, such as urban heat island (UHI) effects, risks of food shortages, and urban waterlogging events, threatening disruptions in food, water, and energy (FWE) domains in cities (Melo et al., 2020), which consequently results in challenges to urban resilience and regional sustainability (Fuhrman et al., 2020). At the same time, the intrinsic intersections between FWE resources, also referred to as the FWE nexus, further reshapes the shocks that were previously contained within a geographic area or a sector and are now becoming globally interconnected (Liu et al., 2018; Zhang et al., 2019), complicating the nexus issues posed to cities (Meng et al., 2019b, Meng et al., 2019a, Meng et al., 2022).
A holistic strategic planning approach known as green and blue infrastructure (GBI) delivers multiple FWE-related benefits from and to urban areas, such as food production, climate regulation, energy savings, flood control, water purification, and rainwater harvesting (Elmqvist et al., 2013). This has significant impacts on urban FWE systems and ensures interconnection, versatility, and support for nature and ecosystems (Mell, 2017). Thus, GBI appears to be a good candidate for improving sustainability of urban systems. With the highlights of sustainable development goals (SDGs), food (SDG2), water (SDG6), and energy (SDG7), are targeted to achieve efficient water use, energy alternative, and agricultural practices (Biggs et al., 2015; Cristiano et al., 2021). In this context, GBI has become a powerful innovation to achieve the SDGs and compact the nexus challenges for urban resilience from the perspective of FWE nexus, through adaptive and flexible implementations (Hoyer et al., 2011; European Commission, 2013; Brink et al., 2016).
GBI consists of a diverse set of green infrastructures (e.g., urban forests, gardens, street trees, urban agriculture, green roofs, green walls) and blue infrastructures (e.g., water bodies, constructed wetlands, rain gardens, permeable pavements, bioswales) (Bellezoni et al., 2021). GBI elements can be woven into a community at several scales and implemented alone or associated with other GBIs. Previous studies classified different GBIs by categories and developed a conceptual framework of the critical links between urban GBI and FWE nexus, together with the direction and magnitude of the relationship. Specifically, GBI provides FWE-related benefits, such as food production, climate regulation, and water supply. As the increasing FWE demands can be satisfied locally, GBI also drives the reductions of emissions and consumptions embodied in the trans-boundary production and supply chains. However, GBI comes at the cost of capital, materials, and energy inputs. The environmental impacts in relation to these inputs are trade-offs for the FWE-related benefits that result from GBI (Bellezoni et al., 2021; Shah et al., 2021). For instance, urban agriculture increases the output of urban edible products in the operation stage and thereby reduces the environmental footprints embodied in the process of external food imports. Whereas during the entire life cycle stages, urban agriculture actuates environmental impacts in different pathways, such as energy input, water irrigation, and greenhouse gas emissions.
Such positive and negative impacts reflect the multiple linkages and trade-offs between urban GBI and FWE nexus, which need to be understood and evaluated within a specific local context and with a variety of stakeholders. Since the disservices of GBI are highly subjective and variable across different environments Haase et al., 2014, Haase et al., 2017 Kremer et al., 2016), the comprehensive examination of GBIs' entire life cycle performances is necessary (Wang et al., 2020). Life cycle assessment (LCA) is a system analysis method that presents an opportunity to assess these trade-offs, compare designs, and choose the most appropriate GBI practices by quantifying a variety of environmental impacts and benefits (Spatari et al., 2011; Shafique et al., 2020). We here, therefore, underline the cardinal role of LCA to systematically capture the intrinsic connections between GBI and FWE nexus considering positive benefits and adverse impacts.
Currently, researchers are paying more attention to the linkages between GBI and FWE nexus. Cristiano et al. (2021) qualitatively reviewed the benefits and limitations of green roofs based on an integrated food-water-energy-ecosystem nexus approach, together with the SDGs. The authors reflected that most of the studies focused on a silo approach, but green roofs should be fully evaluated on the sustainable development of cities and communities through a nexus approach. Melo et al. (2021) established a hybrid framework for forests into a food-water-energy nexus approach, highlighting the critical promotion of forests in food, water, and energy security and societies to achieve SDGs. They also presented three key principles of the food-water-energy nexus: mainstreaming forest restoration, empowering local communities, and implementing nature-based solutions. Caputo et al. (2021) developed a conceptual methodology framework for measuring the resource efficiency, food production, motivations, and health benefits of urban agriculture from the perspective of food-water-energy-people nexus. The proposed framework comprised a combination of methods, such as urban agriculture logbooks, a database of urban agriculture activities, LCA, and material flow analysis, to allow the upscaling of the investigation results from a garden scale to the city scale.
Most of the prevailing quantitative research on GBI and FWE nexus is based on a single aspect, such as direct FWE-related benefits (Moody and Sailor, 2013; Orsini et al., 2014; Winston et al., 2016) or life cycle environmental impacts of GBI (Andrew and Vesely, 2008; Manso et al., 2018; Pushkar, 2019). Some research has further focused on the trade-offs analysis by comparing the positive benefits and adverse impacts of GBI (De Sousa et al., 2012; Wang et al., 2013; Moore and Hunt, 2013; Xu et al., 2021; Shah et al., 2022). More comprehensively, Toboso-Chavero et al. (2019) made a vital advance in measuring the effects of green roofs, including direct benefits (food production, energy generation, and rainwater harvesting), indirect avoidance of carbon emissions, and life cycle impacts at community scale. Despite significant contributions from these studies, there lacks a systematic method introduction to promote the quantification of relevant FWE implications regarding a broad set of GBI categories at the urban scale. Our starting point is to support embracing quantitative explorations to break the understanding obstacles of GBI and FWE nexus and the multiple interplays within them, as the quantitative results would be a cornerstone to guide stakeholders in FWE-oriented resilience planning and governance for urban GBI implementation. Therefore, to overcome the knowledge gaps, we identified the detailed interactions between GBI and FWE nexus and provided an overview of the available methods to quantify the FWE flows and trade-offs of GBI based on the methodological articles.
The rest of this paper is organized as follows: Section 2 outlines the process of review sample selection; Section 3 visualizes the inherent correlations between GBI and FWE nexus; Section 4 introduces the main methods for assessing the FWE-related benefits of GBI; and Section 5 reviews the trade-offs evaluation studies of GBI based on LCA. The conclusions and discussions are drawn in Section 6.
Section snippets
Review methodology
To make this literature review as comprehensive and detailed as possible, a wide range of relevant sources were examined to find published methodological articles. We determined a set of initial keywords according to the authors' expertise and iteratively optimized them through database searching. The retrieved keywords included four aspects: GBI categories, FWE-related topics, research boundaries, and quantitative evaluation. GBI categories were based on the typologies described by
Linkage identification between GBI and FWE nexus
In light of our review, as visualized in Fig. 2, some common aspects of the linkages between urban GBI and FWE nexus are highlighted. In previous research, we have identified the relationship between different types of GBI and FWE nexus (Bellezoni et al., 2021). Further, in this paper, we focus on the inherent correlations between GBI and FWE nexus to guide the quantification of their linkages. As shown in Fig. 2, GBI can offer great FWE-related benefits to the environment and human beings,
Quantification of the FWE-related impacts of urban GBI
This section aims to outline the quantitative methods of the implications of GBI in relation to FWE domains, including food (local food production), energy (climate regulation, energy saving, and energy generation), and water (runoff control, rainwater collection, and water purification), where provides the method introductions and specific cases, more details are presented in the following tables.
Life cycle assessment to quantify the trade-offs of GBI
This section aims to outline the relevant studies to capture GBI's trade-offs based on the life cycle thinking, given that a silo lens of FWE-related benefits of GBI cannot reflect the comprehensive implications of GBI on FWE nexus. Regarding previous trade-offs studies, two streams are shown, that is, the trade-offs between life cycle environmental impacts and operational benefits of GBI, and the food-water-energy-carbon nexus trade-offs of GBI in the upstream production and supply chains. The
Conclusions and Discussion
Urban GBI has gained increasing popularity for urban resilience and sustainability through adaptive and flexible implementations in the context of current unsustainable paths of urbanization. In particular, research efforts have been made to evaluate the fundamentality of GBI in improving FWE issues since the FWE security nexus topic was released at the conference. This study identifies the detailed connections between urban GBI and FWE nexus and provides a method review for the linkages
CRediT authorship contribution statement
Fanxin Meng: Conceptualization, Supervision, Writing-original draft, Funding acquisition. Qiuling Yuan: Methodology, Investigation, Data curation, Visualization, Writing-original draft. Rodrigo A. Bellezoni: Conceptualization, Methodology, Writing-Review, Editing. Jose A. Puppim de Oliveira: Writing-Review, Editing, Funding acquisition. Silvio Cristiano: Writing-Review, Editing. Aamir Mehmood Shah: Methodology, Data curation. Gengyuan Liu: Writing-Review, Editing. Zhifeng Yang:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We would like to appreciate support from the National Natural Science Foundation of China (No. 72174028) and the Belmont Forum (grant number NEXUS2016: 152); the JPI Urban Europe (grant number 11221480); the NSF, USA (award number 1829224); the FAPESP Foundation, Brazil (grant numbers 2017/50425-9 and 2018/20057-0); Coordination for the Improvement of Higher Education Personnel (CAPES) grant number 88881.310380/2018-01; and National Council for Scientific and Technological Development (CNPq)
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