Mapping urban energy–water–land nexus within a multiscale economy: A case study of four megacities in China
Introduction
Urbanization has been proceeded rapidly [[1], [2], [3], [4]]. Cities occupy less than 5% of the Earth's land surface but contribute to 60%–80% of the global energy, 26% of the fresh water, and 75% of the global emissions [5,6]. Cities play an indispensable role in the sustainable development strategies [4,[7], [8], [9]]. Food, energy, and water (FEW) are the most significant and fundamental natural resources for sustaining the operation of the social system in cities [10]. The resources and environmental conflicts induced by the three “food-energy-water” lifeblood, such as water scarcity, energy insecurity, and food crises, are extremely intense [11].
Due to the interconnectedness of the food-energy-water subsystems and the complexity of an open urban system, it is essential to take a nexus view to identify tradeoffs not only within local supply chains but across regional, national, or even global supply chains [12]. Cities are increasingly at the center of the food-energy-water nexus (FEWN) [13]. Many commodities and services are often produced and traded across the urban natural ecological-economic production-social consumption system boundary [4,[14], [15], [16]]. Considering these complexities, an integrated assessment framework to depict and quantify the physical and virtual resource flows representing the FEW systems is needed to better understand the urban FEWN and to adopt a comprehensive management approach [12,17].
Currently, the conceptual framework of urban FEWN can be summarized from three perspectives: resource interdependency, resource provision, and system integration [18]. Resource interdependency focused on the interdependence of the three resources. It emphasized that the life-cycle production stages (i.e., extraction, production and processing, transportation, and consumption) of any individual resource were determined by the consumption of the other two resources in the urban area [18]. Within this nexus, changing demands for one resource have positive or negative effects on the provision of the other two [12,19,20]. Most previous FEWN researches focused on this dimension. Life-Cycle Assessment (LCA), Material Flow Analysis (MFA), Input-Output Analysis (IOA), and System Dynamics (SD) have been extensively used to simulate the metabolism flows of energy, water, food or land/nitrogen (N)/phosphorus (P) (the representative elements of food system) in one or two sectors of FEW systems. These analyses reflected the level of sectoral technology and resources use efficiencies [[19], [20], [21]], such as the energy–water nexus in the energy and water sectors [[22], [23], [24]], the FEWN in the energy, water, and food sectors [19,20], and the water-greenhouse gases (GHG)-N-P in urban food systems [14].
From the resource provision perspective, the relationships between the underpinning resource availability of FEW systems and its external environment in cities were emphasized [18,25]. That is, the proportional relations of the three resource flows as the inputs and provision to the urban economic system. Within this nexus, the metabolism patterns of the three resource flows embodied in the process of tele-connected transboundary commodities and services production and exchange in urban system were investigated and uncovered [12,[25], [26], [27]]. In those researches, IOA and hybrid analysis method combining the process-based LCA and IOA were widely used to uncover the flow patterns within the urban social-economic systems, such as the energy-water nexus in Shanghai [27], the FEWN in the urban hotel and restaurant sector [28], and FEW intensities analysis in American cities [29].
From the system integration perspective, the urban FEW systems were optimized based on the FEW flows accounting results from both the resource interdependency and resource provision perspectives. Within this nexus, the constraints of resource endowment, development goals, economic development, population, social factors, and different scenario settings to increase the resilience of the urban system were considered [18]. For example, Hu et al. considered two emissions reduction schemes of reducing food loss and waste, and optimizing chemical fertilization to reduce the environmental footprint in the food supply chain, and the effectiveness of emissions reduction measures at the regional scale [14]. However, few studies focused on the system optimization of FEW subsystems in urban economic system due to the high complexity, interconnectedness, transboundary and heterogeneousness of the multielement flows within urban systems. How to evaluate and clarify the multielement nexus of FEW systems within multiple cities is the key and essential condition for urban FEW systems integrations and optimization. Therefore, it is essential to investigate the patterns and characteristics of energy, water, and land resource flows (as the typical elements in FEW systems, hereinafter “EWL”) in multiple cities across the global supply chains, thereby addressing the issues of complicated urban ecological resource management [30,31].
The Multiscale Input-Output (MSIO) model was introduced to study this issue, which was able to evaluate and track the environmental or resource flows in the case of megacities within a multiscale economy. The model enables the direct and indirect cross-boundary flows embodied in domestic and international supply chains outside a city to be traced, quantified, and evaluated. This model has emerged as a critical role for assessing the sustainability of cities in the context of increasing globalization [27,[32], [33], [34], [35]]. In our previous researches, we have employed an environmentally extended MSIO (EE-MSIO) model to track the production- and consumption-based carbon flows of Beijing in the domestic and international regions [26] and quantified the energy-water nexus in Shanghai [27,36]. Furthermore, the heterogeneity of the carbon flows among multiple cities has been explored using the EE-MSIO model [33,37,38].
This study aimed to employ the EE-MSIO model to map the urban production- and consumption-based EWL flows accurately within a multiscale economy. The four megacities in China (i.e., Beijing, Shanghai, Tianjin, and Chongqing) were selected as the cases. The remainder of the paper proceeds as follows: Section 2 introduces the calculation methodology and data source, Section 3 analyzes the EWL resource flows in the case cities within the multiscale economy, Section 4 discusses the policy implications, future directions, and draws the conclusions.
Section snippets
Environmental extended multiscale input-output (EE-MSIO) model
The MSIO model, which sought to include all the product categories within a consistent framework from the multiscale perspective, was proposed based on system theories [39]. The EE-MSIO model was constructed by considering the complexity and multiple relevancies of trade relations. From the production and consumption perspective, it can quantify the relationship between economic activities and environmental pressures at different scales within a multiscale economy [32,37,[39], [40], [41]].
General flows analysis of energy, water, and land
Production-based EWL flows of a city can be classified into three types according to its destinations: local EWL flows represented EWL produced and consumed locally; interregional exported EWL flows represented EWL produced locally but exported to meet domestic regions' demands, and international exported EWL flows represented EWL produced locally but exported to meet foreign countries’ demands. Similarly, consumption-based EWL flows of a city also can be sorted into three types according to
Commonness of urban EWL nexus in megacities
This study used the EE-MSIO model to quantify the production- and consumption-based EWL flows of the four Chinese megacities in 2010. In general, the consumption-based EWL flows were much more extensive than production-based EWL flows, implying that the four megacities were major consumers and typical consumption-oriented cities. Domestic imported EWL flows exceeded domestic exported EWL flows of the four megacities, which means they were net importers or consumers in terms of interregional
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.
Acknowledgments
This research was supported by the National Natural Science Foundation of China (Nos. 71804023), the Fundamental Research Funds for the Central Universities (Nos. 2020NTST15), and the National Natural Science Foundation of China (Nos. 72004035).
References (65)
- et al.
Impacts of local public expenditure on CO2 emissions in Chinese cities: a spatial cluster decomposition analysis
Resour Conserv Recycl
(2021) - et al.
Exploring energy-water-land nexus in national supply chains: China 2012
Energy
(2019) - et al.
The FEW-Nexus city index – measuring urban resilience
Appl Energy
(2018) - et al.
Mapping carbon and water networks in the north China urban agglomeration
One Earth
(2019) - et al.
Critical review of the energy-water-carbon nexus in cities
Energy
(2019) - et al.
Food-energy-water (FEW) nexus for urban sustainability: a comprehensive review
Resour Conserv Recycl
(2019) - et al.
Uncovering urban food-energy-water nexus based on physical input-output analysis: the case of the Detroit Metropolitan Area
Appl Energy
(2019) - et al.
Understanding the impacts of climate change and socio-economic development through food-energy-water nexus: a case study of mekong river delta
Resour Conserv Recycl
(2021) - et al.
City-level water-energy nexus in Beijing-Tianjin-Hebei region
Appl Energy
(2019) - et al.
Water-energy nexus within urban agglomeration: an assessment framework combining the multiregional input-output model, virtual water, and embodied energy
Resour Conserv Recycl
(2021)
Urban energy–water nexus: a network perspective
Appl Energy
Understanding the tele-coupling mechanism of urban food-energy-water nexus: critical sources, nodes, and supply chains
J Clean Prod
Quantification of urban water-carbon nexus using disaggregated input-output model: a case study in Beijing (China)
Energy
Characteristics, influencing factors, and environmental effects of plate waste at university canteens in Beijing, China
Resour Conserv Recycl
Development of an urban FEW nexus online analyzer to support urban circular economy strategy planning
Energy
Urban carbon flow and structure analysis in a multi-scales economy
Energy Pol
Ecological network analysis of carbon emissions from four Chinese metropoles in multiscale economies
J Clean Prod
An embodied energy perspective of urban economy: a three-scale analysis for Beijing 2002–2012 with headquarter effect
Sci Total Environ
From production to consumption: a multi-city comparative study of cross-regional carbon emissions
Energy procedia
Three-scale input–output modeling for urban economy: carbon emission by Beijing 2007
Commun Nonlinear Sci Numer Simulat
Globalized energy-water nexus through international trade: the dominant role of non-energy commodities for worldwide energy-related water use
Sci Total Environ
Global land-water nexus: agricultural land and freshwater use embodied in worldwide supply chains
Sci Total Environ
Three-scale input-output analysis for energy and water consumption in urban agglomeration
J Clean Prod
Land use balance for urban economy: a multi-scale and multi-type perspective
Land Use Pol
Multi-scale water use balance for a typical coastal city in China
J Clean Prod
Transnational city carbon footprint networks – exploring carbon links between Australian and Chinese cities
Appl Energy
Developing a city-centric global multiregional input-output model (CCG-MRIO) to evaluate urban carbon footprints
Energy Pol
Consumption-based CO2 accounting of China's megacities: the case of beijing, Tianjin, Shanghai and chongqing
Ecol Indicat
Transforming our world: the 2030 Agenda for sustainable development
The World's cities in 2016
Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools
Proc Natl Acad Sci Unit States Am
The concept of city carbon maps: a case study of melbourne, Australia: the concept of city carbon maps
J Ind Ecol
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