Researches On Urban Sectoral Energy-Water-Carbon Nexus Analysis Framework And Application Based On Different Perspectives

As one of world's fastest-growing economies,China has been experiencing rapid industrialization and urbanization,with an urbanization rate of 58.52%by 2017.Urbanization gives rise to various environmental issues while promoting the development of economy and society.Specially,cities are accommodating large populations,consuming massive energy and resource,and generating a large amount of greenhouse gases and pollution simultaneously.Therefore,urban sustainability has become urgent and necessary.It is generally believed that urban sustainability is a balanced state between environment,economy,and society.It emphasizes the minimization of resource consumption and environmental destruction and maximization of resource utilization.Energy,water,and CO2,which are measures of urban environment,have a significant impact on urban sustainability.Energy,water,and CO2 are closely related environmental factors in urban systems.Since the variation of single factor will lead to changes of the other two,research on energy-water-carbon nexus is indispensable and of positive significance for promoting urban sustainability.Most of the current study on energy-water-carbon nexus focus on an individual industry,while those focusing on multi-sectors at urban scale are limited.It cannot be ignored that the flow of energy,resource,and other materials depends on trade between sectors,hence,considering the environmental pressure nexus at urban scale and taking the consumption relationship between sectors are necessary.Moreover,estimation on environmental pressures are based on either production or consumption perspective in the majority of energy-water-carbon nexus studies,ignoring the sectoral transmission function for environmental pressures.There exist sectors acting as transmission centers in urban system,which means significant amounts of environmental pressures pass through these sectors along supply chain paths.These sectors,which are key sectors influencing sustainable urban management,may not generate much environmental stress themselves,but transmit considerable environmental pressures.Therefore,it is crucial to analyze enerby-water-carbon nexus based on betweenness perspective.At present,the environmental pressure nexus is not strictly defined,and the concepts of "nexus" in different studies are diverse depending on the type and quantity of the focused environmental factors.There is still much room for exploring the correlation between multiple environmental pressures.Besides,considering the development patterns and industrial structures are discrepant in different cities,the comparison between environmental pressure nexus of cities can provide reference value for decision makers.To address the issues mentioned above,a multidimensional and multivariate analysis framework for urban sectoral environmental pressure nexus based on combination of Environmentally Extended Input-Output Analysis(EEIOA)and Principal Components Analysis(PCA)was proposed in this research.Three dimensions were considered,namely production perspective,consumption perspective,and betweenness perspective.And three viables,which included energy,water,and carbon,were tested.Beijing and Shanghai were chosen as cases to study the urban energy-water-carbon nexus.This research was conducted as follows.Firstly,the sectoral direct energy consumption,direct freshwater withdrawal,and direct CO2 emissions in Beijing and Shanghai were estimated using production-based accounting methods.The direct energy consumption intensities,direct freshwater withdrawal intensities,and direct CO2 emission intensities of sectors in the two study cities were also calculated.By employing PCA,the sectoral energy-water-carbon nexus based on production perspective in Beijing and Shanghai were discussed.The results showed that "manufacture of chemicals and chemical products" was a sector with high energy-water-carbon pressure from production-based perspective in Shanghai.For Beijing,typical sectors with high energy-water-carbon pressure were not found;however,there exist several sectors with "low freshwater pressure,high energy-carbon pressure" and "high freshwater pressure,low energy-carbon pressure".Secondly,the sectoral embodied energy consumption,embodied freshwater withdrawal,and embodied CO2 emissions in Beijing and Shanghai were calculated via EEIOA from consumption-based perspective.The results showed that "transport,storage and post"(Beijing)and "transport,storage and post"(Shanghai)were sectors causing the highest embodied energy consumption in the two cities,with values being 2.30 ×1014 kJ and 4.74 × 1014 kJ,respectively;"farming,forestry,animal production and fishery"(Beijing)and "farming,forestry,animal production and fishery"(Shanghai)were sectors with highest freshwater pressure from consumption-based perspective in the two cities,and the embodied freshwater withdrawal was 6.76 ×108 m3 and 1.52× 109 m3,respectively;"transport,storage and post"(Beijing)and "transport,storage and post"(Shanghai)were sectors generating the highest embodied CO2 emissions,with values of 1.42× 107 t and 3.27 X 107 t,respectively.The pulling relationship between sectors for energy consumption,freshwater withdrawal,and CO2 emissions in the two urban systems were investigated,and the industry pairs with the most remarkable pulling relationship for environmental stress were revealed as follows.In Beijing,the final demand of sector "wholesale and retail trade" drove sector "transport,storage and post" to consume energy with a value of 1.32×1013 kJ;the final demand of sector "manufacture of food and tobacco" drove sector "farming,forestry,animal production and fishery" to cause 1.04×108m3 freshwater withdrawal;and sector"wholesale and retail trade" gave rise to 8.33 × 105t CO2 emitted from sector "transport,storage and post".In Shanghai,sector "manufacture of chemicals and chemical products" cause sector"production and supply of electricity and steam" to consume 3.36×1013 kJ energy;the final demand of sector "accommodation,food and beverage services" drove sector "production and distribution of water" to withdraw freshwater with a value of 2.36 ×108 m3;and the final demand of "wholesale and retail trade" drove 2.02×106t CO2 emitted from sector "transport,storage and post".In this research,PCA was employed to investigate the consumption-based sectoral energy-water-carbon nexus in the two cities.The key sectors driving energy-water-CO2,pressures from upstream were found,which included "construction"(Beijing),"public management,social security and social organization"(Beijing)."scientific research and development,technical services"(Beijing),"manufacture of chemicals and chemical products"(Shanghai),"construction"(Shanghai),and "manufacture of transport equipment"(Shanghai).And these sectors have notable impact on the overall environmental pressures in urban systems.This research provided suggestions for resource and energy saving,CO2 emission mitigation,and urban,sustainability from the perspective of energy-water-carbon nexus,for instance,improving energy structure,improving technologies and equipment,increasing utilization efficiency of upstream products,and using cleaner upstream alternatives,etc.Thirdly,based on EEIOA,structural path analysis(SPA),and the concept of betweenness centrality,the sectoral energy consumption betweenness,freshwater withdrawal betweenness,and CO2 emission betweenness in Beijing and Shanghai were estimated.Via using PCA,the betweenness-based energy-water-carbon nexus is analyzed,and the key sectors acting as transmission centers for energy-water-carbon pressures in the supply chain paths were revealed.The transmission centers included:"production and supply of electricity and steam"(Beijing),"transport,storage and post"(Beijing),"finance"(Beijing),"renting and leasing,business services"(Beijing),"manufacture of chemicals and chemical products"(Shanghai),and "renting and leasing,business services"(Shanghai).This research provided suggestions for urban sustainability from the betweenness-based perspective,and revealed sectors with strong pulling function and high transmission function for environmental pressures in the supply chain paths,which included"production and supply of electricity and steam"(Beijing)and "renting and leasing,business services"(Shanghai)etc.for energy consumption,"accommodation,food and beverage services"(Beijing)and "manufacture of chemicals and chemical products"(Shanghai)etc.for freshwater withdrawal,and "production and supply of electricity and steam"(Beijing)and "renting and leasing,business services"(Shanghai)etc.for CO2 emission.The industries mentioned above should be emphasized during environmental management.And improving the utilization efficiency of upstream products in these industries will promote the overall resource and energy conservation and CO2 emission reduction of urban systems.Fourthly,the environmental stress in Beijing and Shanghai based on each accounting perspectives were compared.The results showed that Shanghai was facing grater environmental challenges than Beijing from the production perspective.Based on consumption accounting method,the embodied energy consumption intensity,embodied freshwater withdrawal intensity,and embodied CO2 emission intensity of most sectors in Shanghai were higher than those in Beijing;the embodied environmental pressures in Shanghai mostly arisen from manufacturing and construction industries,while for Beijing,the embodied environmental pressures were mostly from tertiary industries,especially "scientific research and development,technical services";the disparities in urban functions,industrial structure,and economic development priorities between Beijing and Shanghai resulted in different key consumer sectors driving embodied environmental stress.From the betweenness-based perspective,the energy-water-carbon transmission centers in Beijing were more diverse than Shanghai,of which the energy-water-carbon transmission centers were mainly manufacturing industries.The advantageous industries and the key point in supply chain paths were different in Beijing and Shanghai,which resulted in various transmission sectors in the two cities.This study provided comparisons between accounting results based on three research perspectives of each individual city.The rankings of production,consumption,and betweenness-based results were consistent for several industries,while there existed large gaps between the results based on the three perspectives for some other industries.The alleviation of urban environmental pressures and the urban sustainability achievement require coordination and cooperation of all aspects in the urban system.The urban industries are closely related.The resource conservation,energy saving,and CO2 emission mitigation of an individual industry are not only in connection with the sector itself,but also affected by other industries;and the responsibilities for energy consumption,freshwater withdrawal,and CO2 emission will also vary based on different accounting perspectives.Therefore,it is crucial to formulate environmental management plans on account of the roles played by different industries in the urban system,to improve the efficiency of urban environmental governance,to alleviate urban environmental pressures and to promote urban sustainability.In this research,the multidimensional and multivariate analysis framework of EEIO combined with PCA was applied to investigate the sectoral energy-water-carbon nexus at an urban scale.The pulling function and transmission function of industries for energy-water-CO2 pressures in Beijing and Shanghai were tested based on three dimensions,namely production,consumption,and betweenness perspective.The innovations of this research include:(1)constructing a new multidimensional and multivariate environmental stress analysis framework for urban industries,empirically analyzing the sectoral energy-water-carbon nexus in Beijin and Shanghai,revealing disparities in multivariate environmental stress of Beijing and Shanghai on account of different urban functions,resource conditions,and industrial structure,proposing recommendations for urban sustainability,and enriching research findings on urban multi-environmental-stress nexus;(2)re-examining urban sectoral energy-water-carbon nexus based on betweenness perspective,identifying transmission centers for energy-water-carbon nexus stress in urban systems,recognizing industries that need priority attention in the process of sustainability of study cities on account of three research perspectives,and providing a new angle and a methodology reference for researches on urban environmental pressure nexus.The significance of this research includes the following.From the theoretical perspective,this study provides a new multidimensional and multivariate analysis framework for energy-water-carbon nexus research.Specially,the urban sectoral energy-water-CO2 pressures were discussed from a perspective of betweenness,and the betweenness-based results were combined with the production and consumption-based results to explore the roles played by each urban industry in terms of environmental stress.The study fills previous research gaps to a certain extent.From the application perspective,the production,consumption,and betweenness-based energy-water-carbon nexuses in Beijing and Shanghai can provide comprehensive profiles of sectoral environmental pressures and reveal the pulling and transmission function for energy-water-CO2 stress of each sector.This research can propose industry-specific recommendations for energy conservation,water saving,and CO2 emission reduction;and the results can provide data support for sustainability strategy-making.The analysis framework proposed by this study can be further applied to other cities and regions and can be used to investigate multi-environmental-factor nexus,which will have reference value for decision makers.