Elsevier

Energy

Volume 239, Part B, 15 January 2022, 122038
Energy

Mapping urban energy–water–land nexus within a multiscale economy: A case study of four megacities in China

https://doi.org/10.1016/j.energy.2021.122038Get rights and content

Highlights

  • EE-MSIO model was used to analyze production- and consumption-based EWL flows in four Chinese megacities.

  • Production- and consumption-based EWL flows of these four megacities exhibited different features.

  • Consumption-based EWL flows were higher than production-based EWL flows in all four megacities.

  • All four megacities were net EWL importers in terms of interregional trade.

Abstract

Energy, water, and land (EWL) are typical elements in urban food-energy-water systems. With the expansive growth of urbanization and the economy, the demands for EWL keep increasing and pose significant challenges to urban sustainability. Previous studies mostly focused on one or two elements flows through sectoral approaches while ignoring the interconnectedness of food-energy-water subsystems and the complexity of an open urban system. Here, we adopted a nexus view to track the urban EWL flows not only within local but also across regional, national, and even global supply chains from the production- and consumption-based perspectives using the environmentally extended multiscale input-output model (EE-MSIO). The four Chinese municipalities (i.e., Beijing, Tianjin, Shanghai, and Chongqing), also known as megacities, were selected as our cases. Our results revealed that all four megacities were consumption-oriented cities for EWL resources. Nearly 72%–77%, 87%–92%, and 95%–99% of the consumption-based energy, water, and land flows were sourced from outside the geographical boundaries of Beijing, Tianjin, and Shanghai, respectively. Domestic regions were the major suppliers for the four megacities. This analysis can help policy-makers to develop more effective and targeted strategies for complicated urban ecological resources management.

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).

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