Energy Policy 124 (2019) 13–22 Contents lists available at ScienceDirect Energy Policy journal homepage: www.elsevier.com/locate/enpol Characterizing the metabolic pattern of urban systems using MuSIASEM: T The case of Barcelona ⁎ ⁎⁎ Laura Pérez-Sáncheza, , Mario Giampietroa,b, , Raúl Velasco-Fernándeza, Maddalena Ripaa a Institut de Ciència i Tecnologia Ambientals (ICTA), Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain b ICREA, Passeig Lluís Companys 23, Barcelona 08010 Spain A R T I C LE I N FO A B S T R A C T Keywords: The extreme degree of openness of contemporary urban systems with regard to both economy and population End-use matrix creates a serious challenge for the study of urban energy metabolism. A novel tool based on Multi-Scale Urban metabolism Integrated Analysis of Societal and Ecosystem Metabolism (MuSIASEM) is proposed to overcome these chal- MuSIASEM lenges. It consists of an end-use matrix, a coherent multi-level integrated characterization of the uses of different Energy forms of energy carriers (electricity, heat, fuels) for the various tasks performed in the city, including private and Cities Time allocation public mobility, tourism, commercial and residential activities. The end-use matrix integrates quantitative data referring to different dimensions (i.e. energy, human activity, land use, value added) and hierarchical (economic sectors and functional elements at lower levels) and spatial scales (i.e. individual buildings, neighborhoods, and the city as a whole). The end-use matrix provides information on both extensive (flows) and intensive variables (flow/fund ratios or benchmarks). Benchmarks are important for policy-making and allow a meaningful com- parison of energy performance across hierarchical levels within the urban system, and among different urban systems. The approach is illustrated for Barcelona, a global city characterized by an important service sector. 1. Introduction systems with regard to both economy and population creates a serious challenge for the study of urban energy metabolism and the develop- Since ancient times cities have been the center of the economy and ment of local energy and climate policies: Who is consuming energy in power of nations (Braudel, 1979). They specialize in consuming goods the city to do what? and services while concentrating the command and control over the rest From a thermodynamic perspective, cities represent dissipative of the territory, shaping and guiding the process of economic devel- systems, constantly importing and exporting energy and matter across opment (Jacobs, 1984). On the flipside, though, this specialization their boundaries (Dyke, 1988; Prigogine and Nicolis, 1977). A city “can makes cities highly dependent on activities taking place in the near or only survive as long as it is a center of inflow of food, fuel and other distant periphery, such as agriculture, mining, and ecological services. commodities and sends out products and waste” (Prigogine and Nicolis, Recent globalization has reshaped cities worldwide by generating an 1977, p. 4). The openness of cities and their dependence on processes international division of labor. Notably global cities in post-industrial taking place outside their borders has also been described as ‘entropy societies have almost fully externalized manufacturing (secondary debt’ (Dyke, 1988; Straussfogel and Becker, 1996). Therefore, the idea sector) to less developed countries and have become ‘purely dissipative that cities are metabolic systems (Wolman, 1965) is consistent with the systems’ (Dyke, 1988), expressing activities mainly in the service, thermodynamic perspective. The metabolism of human society is not a government and residential sectors (Sassen, 2010). Due to improved new notion. It has been used to characterize the processes of energy and and cheap transport services and global cities being attractors of ac- material transformation in society required for its continued existence tivities generating high value added, an increasingly large share of (Cottrell, 1955; Lotka, 1956, 1922; Ostwald, 1911, 1907; Soddy, 1926; urban activities is performed by people living outside the city (Miralles- White, 1943; Zipf, 1941). Overviews of the application of the concept Guasch and Tulla Pujol, 2012). Thus, globalized cities are not only have been provided by, among others, Martínez-Alier (1987) and ‘made of’ residents, but also an important number of commuters and Fischer-Kowalski and Hüttler (1998). tourists. The extreme degree of openness of contemporary urban While thermodynamic considerations indisputably provide a sound ⁎ Corresponding author. ⁎⁎ Corresponding author at: Edificio ICTA-ICP (Z), UAB Campus de Bellaterra, 08193 Bellaterra, Spain. E-mail addresses: laura.perez.sanchez@uab.cat (L. Pérez-Sánchez), mario.giampietro@uab.cat (M. Giampietro). https://doi.org/10.1016/j.enpol.2018.09.028 Received 15 March 2018; Received in revised form 18 September 2018; Accepted 21 September 2018 0301-4215/ © 2018 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 general framework for understanding cities and their evolution, op- transport sectors). In particular, the end-use matrix identifies which erational representations of urban metabolism and corresponding in- types of energy carriers are used, how much, where, when, by whom dicators of sustainability are yet to be developed (Filchakova et al., and to what purpose (why). Besides energy, the end-use matrix con- 2007). A similar concern has been expressed by Zhang et al. (2015): siders additional dimensions of analysis, such as human time allocation, “Practical methods of analysis need to be improved. Future analysis land use, and value added, thus providing an integrated characteriza- should focus on establishing a multilevel, unified, and standardized tion (Velasco-Fernández, 2017; Velasco-Fernández et al., 2018). The system of categories to support the creation of consistent inventory end-use matrix has previously been studied at the national level databases”. This challenge requires the exploration of new transdisci- (Velasco-Fernández et al., 2018), but not yet at the urban level. plinary approaches, as emphasized by Dijst et al. (2018): “the need to come to a better understanding of the different disciplinary perspectives 2.2. Construction of the urban end-use matrix: defining constituent on urban metabolism through identifying and analyzing the flows and components drivers”. This paper presents the results of an exploratory application of The identity of the city depends on the specific mix of its functional Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism and structural elements whose maintenance and reproduction is re- (MuSIASEM) to urban energy metabolism, using the city of Barcelona as quired to preserve ‘the whole’. Therefore, the first step in the con- a case. The aim of the work is to show that, despite the challenges posed struction of the end-use matrix for an urban system is the definition of by the extreme degree of openness of urban systems, it is possible to: (i) the city's constituent components associated with the definition of ‘why generate a coherent multi-level integrated characterization of the uses energy is used’ (‘final causes’). The functions (or categories of socio- of different forms of energy carriers for the various tasks performed in economic activities) of the energy transformations are needed for the the city (i.e. private or public mobility, tourism, commercial activities, maintenance and reproduction of the city's constituent components. residential activities), and (ii) integrate quantitative data referring to Constituent components are defined in relational analysis (Rosen, different dimensions (i.e. energy, human activity, land use, value 1991) as the parts that are essential to preserve the identity of a self- added) and hierarchical/spatial scales (i.e. individual apartments, producing system (that what has to be reproduced). In MuSIASEM, neighborhoods, districts and the city as a whole). We discuss the pros following Georgescu-Roegen's flow-fund scheme (Giampietro et al., and cons of the proposed approach and illustrate the importance of the 2012), the size of the constituent components is measured by looking at analysis for guiding practical decision support and help local govern- the size of the fund elements making up the constituent components. ments achieve sustainable development goals. The two funds used for this task are: Human Activity (in hours per year) The contents of this paper are organized as follows. Section 2 pro- and Area of Built Environment (in square meters). vides the theoretical framework of the proposed approach and the de- Human activity relates to the time spent inside the city boundaries. scription of the construction of the end-use matrix. In Section 3, the In quantifying this human activity (in hours per year), it is important to end-use matrix is further explored for the case study of Barcelona. The not only assess the total hours/year in relation to the chosen categories conclusions are presented in Section 4, together with a reflection on of functional activity (what is done and how), but also to further char- further research needs and complementary approaches, as well as acterize the constituent component: Who is allocating these hours? policy implications. Notably for urban systems, this information is essential to understand the why, the final cause of the functional activity. Indeed, because of the 2. Methodology extreme openness of urban systems, the elaboration of the end-use matrix at city level introduces a novel feature in the MuSIASEM ac- 2.1. MuSIASEM and the energy end-use matrix counting, that is, the distinction between activity of residents, com- muters (people entering the city to work on a daily basis), and tourists MuSIASEM has been specifically developed for studying the com- (people visiting for short periods). plex metabolic pattern of social-ecological systems at different hier- The second fund element is the controlled area of built environment archical levels, scales and dimensions of analysis (economic, social, or ‘useful surface’, defined as available area devoted to end-uses (in demographic, ecological, etc.) (Giampietro et al., 2013, 2012, 2009, m2). It is composed of ‘land uses’ (e.g. streets, parks, the port) and 2006; Giampietro and Mayumi, 2010, 2000, 1997; Pastore et al., 2000; ‘building uses’ (internal area of buildings). This component allows a Ramos-Martín et al., 2007). It provides a quantitative representation of spatially explicit analysis in regard to the chosen subdivision. In this the metabolic pattern of the system under study in relation to two non- particular study, administrative areas (neighborhoods or ‘barrios’ in equivalent views: internal viability (inside view) and external feasibility Spanish) have been selected as constituent component. (outside view). Internal viability refers to the functions (tasks) ex- Note that the decision of how to define constituent components is an pressed by the system needing a pertinent combination of structural exercise that is normative by definition. Hence it would require a co- elements capable of metabolizing specific input flows required to ex- production process with the users of the analysis (Giampietro, 2018). press these tasks. Internal viability is analyzed with the end-use matrix (Velasco-Fernández, 2017; Velasco-Fernández et al., 2018). External 2.3. Construction of the urban end-use matrix: functional characterization feasibility concerns the interaction of the system as a whole with its context. Indeed, the ability to sustain the metabolic pattern of the The identification of the constituent components is necessarily whole depends on the existence of an adequate supply of inputs (e.g. linked to the functional characterization of the system. In this way we energy, water, minerals) and an adequate sink capacity for absorbing can identify the functions required for their reproduction. We use the wastes and emissions. In MuSIASEM, external feasibility is assessed by definition of categories of human activity expressed inside the system the ‘environmental pressure matrix’ (requirement of primary sources boundaries to identify a taxonomy of functions stabilizing the activities and primary sinks from the local environment) and ‘externalization of residents, commuters and tourists and maintaining and reproducing matrix’ (the primary sources, primary sinks and end-uses embodied in the spatial patterns found in barrios. This step involves the translation of imports from outside the system boundaries) (Ripa and Giampietro, the implications of final causes (what a desirable city should be and 2017; Ripoll-Bosch and Giampietro, 2018). We focus here only on the should do) into the definition of a set of functional elements capable of analysis of the end-use matrix. expressing the required tasks. This is illustrated in Fig. 1 for the city of The energy end-use matrix is a tool for analyzing in a coherent way Barcelona. Note that the primary sector is not included in Fig. 1, it how different energy carriers (electricity, fuel, process heat) are used to being virtually completely externalized outside the city boundaries—a perform different end-uses (e.g. inside the household, industry, feature common to all service cities. 14 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 Fig. 1. Dendrogram of functional categories across hierarchical levels for the Barcelona case study. Table 1 Data array used in the analysis. Variables are defined in Table 2. Ext. var. Intensive variables Extensive variables HA US EMRelec EMRheat EMRfuel EJP EMDelec EMDheat EMDfuel EUSP ETelec ETheat ETfuel GVA Funds Flow/Fund Flow As shown in Fig. 1, the function ‘Services and Government’ maps human activities in the economy (e.g. residential, use of services, part onto eight functional elements (education, healthcare, offices, com- of the mobility) and the hours of human activity related to a service merce, bars, restaurants & hotels, transport, other). Hence, at the level (the hours of the worker and the users). This is illustrated in Fig. 1. It is of functional elements we identify typologies of processes associated to important to note that, human activity being a fund, the accounting of specific tasks. Note that in order to express the expected tasks, func- the hours of human activity must preserve closure across hierarchical tional elements must be linked to structural types, that is, typologies of levels of analysis: the size of the system (expressed in hours) must re- organized structures needed to express the task. For example, the main the same when accounted across different categories of human functional element ‘transport’, defined at hierarchical level n-3, can be activity referring to different levels of analysis (from n to n−4). further sub-divided into functional elements at level n-4. These lower- level functional elements (e.g. private mobility) in turn map, at level n- 2.4. Construction of the urban end-use matrix: data arrays, extensive and 5, onto structural elements (e.g. cars, motorbikes, vans, trucks, buses). intensive variables A parallel accounting of the profile of allocation of human activity in the service sector is introduced in the end-use matrix. This represents Each element in the dendrogram of functional and structural ele- another important novelty compared to earlier work. Indeed, for many ments illustrated in Fig. 1 is associated with a data array that is shown of the activities taking place in the service sector there is a simultaneous in Table 1. The data array consists of extensive variables (funds and requirement of human activity both on the supply side (e.g. people flows) and intensive variables (flow/fund rations). Variables are de- working in a restaurant or bus drivers) and the demand side (e.g. cus- fined in Table 2. The two fund coordinates (human activity and useful tomers of the restaurant or passengers riding on the bus). Changes in surface) are used to map the size of constituent components introduced human activity may entail a non-linear change in the feasibility of the in Section 2.2, and as external referents to contextualize the assessment dynamic equilibrium between the human activity needed to consume of flows. That is, energy flows are expressed in relation to a specific goods and services and that required for the production of goods and category of human activity. services (Zipf, 1941). Therefore, at the urban level, we analyze the si- In this study, four different flows are considered; three relate to multaneous investment of two distinct types of human activity: ‘Outside energy carriers (Giampietro and Sorman, 2012) and one to monetary paid work’ (e.g. passengers in a bus, customers having lunch in a res- flows, following the classification by Velasco-Fernández et al. (2018): taurant, or taking a guided tour) and ‘Paid work’ (e.g. workers as bus (i) energy throughput electricity; (ii) energy throughput heat; (iii) en- drivers, waiters, tour guides). These two sets of accounting categories ergy throughput fuels; (iv) gross value added. are shown in Fig. 1. The category ‘Outside paid work’ is further sub- In the accounting any flow of energy carrier (a quantity per year in divided into: Residential, Mobility, Use of services and government MJ or kWh) or money must always be associated with a defined size of (henceforth Use of SG), and Other outdoor activities. The category ‘Paid fund element metabolizing it. In this way the intensive metabolic Work’ is split into: Services and Government (SG), Port, Construction characteristics of the fund element can be defined, namely the pace and Manufacturing (CM), Energy Sector. (e.g. MJ of fuels per hour of human activity) and the density of the This novelty allows the simultaneous characterization of unpaid flows (e.g. kWh of electricity per m2 of useful surface). The use of 15 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 Table 2 Description of the variables used in the analysis (intensive variables are averages per year). Indicator Definition Unit HA Human Activity time invested in the end-use per year h US Useful Surfaces quantity of area devoted to the end-use km2 EMRi Exosomatic Metabolic Rate ETi/HA: amount of energy carrier i metabolized per hour of work allocated to the end-use kWh/h or MJ/h EJP Economic Job Productivity GVA/HA: value added per hour invested in the end-use €/h EMDi Exosomatic Metabolic Density ETi/US: amount of energy carrier i metabolized per quantity of area devoted to the end-use kWh/m2 or MJ/m2 EUSP Economic Useful Surfaces Productivity GVA/US: value added per area of end-use €/m2 ETi Energy Throughput Amount of energy throughput metabolized in the form of energy carrier i (electricity, heat or fuel) by kWh/year or MJ/year the end-use. GVA Gross Value Added Value of goods and services produced by the end-use €/year intensive variables is essential to establish an accounting scheme across the end-use matrix in a participatory way, involving the users of the different hierarchical levels. These ratios can not only be used to analysis in the choice of final causes and the corresponding relevant compare qualitative aspects of the metabolic pattern among hier- categories for the functional and structural elements; (ii) involvement archical levels of a given city, but also to compare different cities or of local experts to double check the robustness of data and assumptions; evaluate the performance of an activity against reference values (iii) carrying out the analysis in an iterative way, starting with a pre- (benchmarks). Regarding the calculation of benchmarks (e.g. con- liminary set of results where the numbers included in the multilevel sumption of energy carriers per hour of a service) we can either con- end-use matrix should be considered place-holders and then going sider the metabolic rate in relation to the human activity of the workers through the activities described in the previous two points to improve or that of the users, thus generating a more detailed characterization of the robustness and the quality of the analysis. its performance. 3.2. Description of the urban system and system boundaries 2.5. Data sources Barcelona is the second most populated city in Spain (after Madrid) Data from a large number of diverse sources are needed to imple- and the capital of the region Catalonia. With a population of 1.6 million ment the end-use matrix, including throughput of energy carriers, value inhabitants in 2012 and occupying 102 km2, it is also one of the most added, useful surfaces and human activity. Generally, these data come densely populated cities in Europe. from distinct disciplines, often using different classifications, definitions Barcelona is divided in 10 administrative districts and 73 neigh- and units of analysis, and are often not sufficiently disaggregated to fit borhoods or barrios (Ajuntament de Barcelona, 2012). Barrios are het- the defined organization of the system. This poses a serious challenge to erogeneous in size, age, type of construction, availability of services, transdisciplinary analysis but, at the same time, is an indispensable step demography, income and other characteristics. The city of Barcelona is to analyze the urban system in all its complexity. Intensive variables in turn part of a larger administrative unit, the metropolitan area of can be calculated from extensive variables (top-down assessment). Barcelona (AMB), which besides Barcelona includes also the urban However, where data on extensive variables are difficult to obtain, agglomerations around the city. The AMB had 3.3 million inhabitants in benchmarks for intensive variables from similar systems or elements 2012 (Àrea Metropolitana de Barcelona, 2012). The system boundary can be used to estimate extensive variables (bottom-up estimation). chosen for the validation of the end-use matrix is the administrative The sources of data for this exploratory analysis were diverse and domain of the city of Barcelona and the reference year is 2012. involved meetings with relevant actors in the city administration of The main economic sector of Barcelona is the service sector both in Barcelona. General socio-economic data, value added and useful surface monetary terms (88,7% of the value added) and in number of workers data were obtained mainly from the statistical office of the city council (84,5%) (Ajuntament de Barcelona, 2012). The manufacturing sub- (Ajuntament de Barcelona, 2016, 2012). The Local Energy Agency of sector is progressively losing importance in the economy of the city Barcelona provided valuable data on energy carriers for households, (Barceló and Solà, 2014). Logistics has a strategic importance, with the services and mobility, which were then complemented with energy data port of Barcelona being one of the most important ports in Spain and from other sources. Human activity data were derived from two distinct the Mediterranean Sea, both in terms of passengers and volume of sources: the time use survey of Catalunya (IDESCAT, 2012) and the goods. Relying on its natural gas import facilities, the port houses a statistics on number of workers (Ajuntament de Barcelona, 2012). A combined cycle power plant (850 MW), which is the only large-scale detailed list of sources and an explanation of the calculations is avail- electricity generation plant inside the boundaries of the city. Fishery is able in Giampietro et al. (2018). not a significant economic activity (Port de Barcelona, 2012). 3. Results and discussion 3.3. Human activity 3.1. Disclaimer The fact that Barcelona is surrounded by other smaller urban ag- In this section we validate the energy end-use matrix for the city of glomerations, a characteristic shared by many cities, poses serious land Barcelona. It is important to realize that the main purpose of this paper constraints and creates an intense daily commuting between munici- is the exploration of a new approach to operationalize the concept of palities (see Table 3). Indeed, tourists and commuters play an important urban metabolism. We do not pretend providing robust numerical re- role in shaping the identity of Barcelona and its economy. Their roles sults for actual use in local policy making. At present, the sole goal of are expressed in their contribution to the overall human activity in the this work is to illustrate the possibility of organizing, in a coherent way, city, as shown in Fig. 2. For example, the paid work in Barcelona is the various pieces of quantitative (including spatially explicit) in- equally distributed between residents and commuters, and a significant formation required to characterize, monitor and control urban energy share of services (leisure, commerce and education) is used by tourists performance. Generation of data useful for decision-making would re- (22%). quire the fulfillment of three additional conditions: (i) construction of 16 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 Table 3 and products, providing benefits and services to the whole foreland and Million trips (one way) made in a working day inside Barcelona and from or to hinterland. All the same, as the port is an important node of an inter- Barcelona (IERMB, 2013). national transport network it is an essential component of the city of Trips (one way) Internal From or to Barcelona Barcelona, facilitating the externalization of the functions of the pri- mary and secondary sectors at worldwide scale. Active (walking, bike) 2.85 0.07 As concerns the energy sector, the port houses the only relevant Public transport 1.45 0.88 power plant (a combined cycle thermoelectric plant) producing elec- Private transport 0.66 0.77 tricity. The plant is used as a peak producer, and relies on imported natural gas. Other large power plants are located outside the city 3.4. Energy end-use matrix of Barcelona boundaries and local photovoltaics produce only a mere 0.2% of elec- tricity (Observatori de l’Energia de Barcelona, 2013). Considering that In Fig. 3 we first show a simplified energy end-use matrix for Bar- the plant consumes all of the heat energy consumed in Barcelona's celona. On the other hand, Fig. 4 represents the complete energy end energy sector (11.8 ×103 TJ) and has an efficiency of 58%, it produces use matrix, including US, VA and the corresponding flow/fund ratios. 1896 GWh or approximately 25% of the total electricity consumed in As described in Section 2.4, the information in the end-use matrix is the city. organized in the form of data arrays, with each row describing the profile of inputs required to express a specific function. The top-row 3.5. Example of lower-level analysis refers to Barcelona as a whole (level n), whereas the other rows de- scribe lower-level functional compartments (levels n-1 and n-2). As An example of lower-level analysis is shown in Fig. 5 for the Ser- shown in Fig. 3, the largest share of ‘paid work’ activity in Barcelona is vices and Government sector. It describes the metabolic pattern of its allocated to the ‘services & government’ (SG) sector: 1.5 × 109 h immediate lower-level (level n-3) elements: education, healthcare, of- compared to 0.3 × 109 h allocated to ‘manufacturing & construction’ fices, commerce, hotels, bars and restaurants, transport and other. At (MC). The SG sector presents the highest metabolic rate for electricity this level we can define the characteristics of functional and structural (EMRel) compared to the other ‘paid work’ sectors, thereby making SG elements in relation to more specific definitions of activities developed the dominant electricity (ETel) consumer in absolute terms, but the inside the sub-sector. As we have already seen, the SG sector, including lowest for heat. Indeed, despite the large share of human activity in SG, both services to people and companies, is the largest sector in Barcelona the ES and MC sectors are the largest overall heat consumers (ETheat). in terms of ETelec, ETfuel, value added (VA) and HA. As shown in Fig. 5, Comparing the EMRs of Barcelona's MC sector (EMRel = 1.7 kWh/h, ‘Offices’ is its main subsector in terms of HA and VA, and also has the EMRheat = 24 MJ/h, EMRfuel = 0 MJ/h) with the average of Europe highest EJP (except transport) and EUSP (value added per area of end- (EMRel = 16 kWh/h, EMRheat = 103 MJ/h, EMRfuel = 7.1 MJ/h) use). However, it has relatively low EMRs compared to the other sub- (Velasco-Fernández, 2017), we may conclude that the city is doing sectors. relatively well. However, the relatively low rate of energy carrier The Barcelona city council has presented a strategic plan that aims consumption is due to the specific composition of Barcelona's MC at further boosting its transformation in global city. The 22@ area, sector, consisting mainly of construction (which is characterized by the formerly an industrial area is projected to become “a system of innova- lowest EMRs in the MC sector) and manufacturing of vehicles (mainly tion- cutting edge companies, universities and training centres, and centres of assembling).F research and transfer of technology” (Ajuntament de Barcelona, 2018) In the specific case of Barcelona, the port deserves attention. It ex- with the final aim of making Barcelona the “capital of innovation” hibits relatively high metabolic rates (EMRs) and high economic job (Europa Press, 2017). The creation of new office buildings, increasing productivity, due to the use of heavy machinery and relatively low economic activity, recruiting unemployed people and/or attracting requirement of human labor typical of logistic ports (compared to ports more workers to the city (no substitution of economic activities, but net with shipyards). The relevance of this infrastructure for the city is dif- increase), will increase energy consumption no matter how efficient ficult to assess both in monetary and biophysical terms since it carries new infrastructures will be. The effect on the urban energy metabolism out international shipping both for exports and imports of energy, food of replacing an abandoned industrial area with services can be Fig. 2. Tracking the amount of investment of human activity (in hours) of the constituent components. LCE = leisure, commerce and education. LCE + hotels = Use of SG. 17 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 Fig. 3. Simplified end-use matrix characterizing each function with the Energy Throughput (ET), hours of Human Activity (HA) and their metabolic ratios (EMR). Fig. 4. Energy end-use matrix of the levels n, n-1 and n-2 of Barcelona. Fig. 5. Example of an end-use matrix from the Services and Government Sector of Barcelona. anticipated by an analysis based on the end use matrix. and ‘Public Transport’ (see Fig. 1). All the same, the effect of policies aimed at reducing private mobility in favor of public transport (a re- distribution of human activity across the two subcategories) must be 3.6. Digging deeper into the end-use matrix: consumption versus production studied in relation to changes in the generic function ‘Mobility’, both in in the service sector the paid work sector (service provision) and outside of the paid work sector (service consumption). The latter is illustrated in Fig. 6. Another important feature of the end-use matrix is that the func- Indeed, for the service sector the amount of human activity of the tional categories can be expanded depending on the need for detail in users (e.g. bus passengers) is as important as that of the workers pro- relation to decision-making. For example, when dealing with transport viding the service (e.g. bus drivers). For this reason, we have (mobility) (Fig. 6) we can further distinguish between ‘Private Mobility’ 18 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 Fig. 6. Special End-use Matrix describing the metabolic pattern associated with the final cause “Mobility” using categories of Human Activity defined in Outside Paid Work”. established a parallel accounting of the hours of human activity allo- However, there is no evident relation between these two variables and cated to services including the human activity of both users (in the EMD. In addition to family income and area per capita, two other outside paid work sector) and workers (paid work sector) (see Fig. 1). variables have been considered: (i) year of construction of the build- This parallel accounting permits a comprehensive evaluation of the ings; (ii) the multi-story index of residential buildings (MSI) reflecting services not only in terms of labor force and capitalization (e.g. the the number of floors of the residential buildings. While our exploration power capacity and the type of devices required for providing the ser- shows some trend for the majority of barrios there is a considerable vices based on the energy consumed per hour of paid work), but also in number of outliers having high EMD at low building use per inhabitant, relation to the quality of the service (i.e. time spent by in using the low family income and low MSI. These outliers, possibly due to the low service). The same rationale can be applied to other types of services. density of buildings, represent a low share of the population. Indeed, For instance, the analysis of the number of hours of paid work per user there are many other factors that have to be considered in a spatially is a useful indicator for analyzing the quality of caring services (e.g. explicit analysis of EMRi and EMDi. hospitals, nursing homes) and education (e.g. schools). In this way it This brief exploration of energy use in the residential sector by becomes possible to generate diverse indicators of material standard of barrios shows the possibility of incorporating spatially explicit analysis living for the city. in our approach, thus providing a holistic view of the different func- Returning to mobility, an assessment of distances (shown in Fig. 6) tional compartments defined in the end-use matrix. Further multi- is another interesting feature. In the specific case of Barcelona, private variate analyses are required for specific case studies in order to provide motorized mobility consumes about two thirds of the total fuels in robust information for policy-making. Also, in order to better visualize mobility. Active modes of transport (walking or cycling) are those results, further work is need to develop user-friendly maps and graphs. where most time is spent, but less kilometers are covered (after taxis). 4. Conclusion and policy implications 3.7. Spatially explicit analysis—neighborhoods Proper accounting of urban energy metabolism is of paramount For the residential sector (subsector of the Outside Paid Work sec- importance for policy making. Cities are open systems and heavily rely tor—see Fig. 1), a spatially explicit analysis by barrios was explored on trade for their energy and food security and on flows of commuters through the construction of an end-use matrix characterizing the re- and tourists. This makes any analysis of urban energy metabolism ex- sidential sector for each barrio (a total of 73 barrios in Barcelona). tremely complex. We have shown for the city of Barcelona that the Preliminary results are shown in Fig. 7, showing graphs exploring various forms of energy carriers (electricity, heat, fuels) are used in correlations of EMR and EMD with four variables (e.g. family income, different combinations and at different rates for different purposes. This building use per inhabitant, multi-story index, and year of construction) multi-level analysis is useful for identifying the relevant factors that characterizing the barrios. While barrios are heterogeneous among each determine the energy metabolism of the city: What activity is the lar- other, they are internally sufficiently homogeneous in terms of socio- gest consumer of what type of energy carrier? Is this consumption ne- economic conditions and built environment to assume that their cessary and why? How does Barcelona express this function compared average characteristics enable an identification of factors affecting en- to other cities? Is there room for improvement? ergy use. Note that for this analysis the assessment of energy end-use is Achieving the general target of a 40% reduction of greenhouse gas calculated as the thermal equivalent of the overall gross energy re- emissions by 2030, as proposed by the Covenant of Mayors (https:// quirement using the partial substitution method (Giampietro and www.covenantofmayors.eu/en/), is a major challenge for cities. Sorman, 2012). This is a reasonable step given that, according to the Strategies toward reaching this general target must necessarily be city- data provided by Local Agency of Energy of the city, the relative con- specific and carefully consider the potential implications on the delicate tribution of heat and electricity to the total energy consumption is al- equilibrium of the many different functions carried out in the city most the same in all barrios. In the residential sector, EMR (the overall (residences, economic sectors, etc.) as well as the city's dependence on rate of energy consumption) may be assumed to be a proxy of the trade (mining, agriculture, industry, transport) and movements of material standard of living as it reflects the number of appliances me- people (e.g. tourists, commuters, immigrants). The quality of specific tabolizing energy inside the dwellings. EMD (the density of overall technological solutions (energy performance) can only be assessed in energy consumption in residential useful surfaces) is a variable already relation to an identified function or task (e.g. private mobility, re- in use in technical assessments of energy efficiency of buildings. It in- sidential, public mobility, construction). The more we move the ana- dicates the actual energy carrier consumption per m2 of the house lysis of the metabolic pattern to a lower level of analysis, the better we (Building Use, BU). can identify benchmarks that allow comparing ‘apples with apples and The results in Fig. 7 show that in our specific case of Barcelona the oranges with oranges’ when studying the performance of different ci- EMR is correlated with Building Use per inhabitant and family income. ties. On the other hand, general targets set for technical processes (e.g. The shapes of the two graphs are similar as these two variables are efficiency of buildings) or economic sectors (e.g. transport efficiency in correlated among each other (wealthy people having bigger homes). terms of kWh/ton-km) not necessarily reflect the impact of energy 19 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 Fig. 7. Exploring the effect of different factors on the metabolic characteristics of the residential sector at level n-5 (73 barrios). savings at the local (sectoral) level on city-level performance. Different (ii) useful surfaces (classified by area of neighborhoods). The metabolic cities express different functions, in different ways, using different types characteristics of the main sectors of the system (Paid Work: services of technologies and different mixes of primary energy sources. Policies and government, port, manufacturing and construction, energy sector; based on assessments or comparisons of aggregate levels of energy Outside Paid Work: residential sector, mobility, use of SG, other ac- consumption or emission risk missing this diversity. tivities) are defined in the form of benchmarks. Detailed analyses can be A second important point to consider is that transformations of performed at lower levels (sub-sectors), as has been shown for the energy in a city are complex. It is essential to acknowledge that not all services and government sector of Barcelona. As regards mobility, the joules are the same. Energy carriers have different qualitative char- accounting scheme also covers an assessment of the human activity of acteristics (electricity vs fuels) and this difference must be maintained the users of services, the identification of structural elements (private in the accounting. In addition, an integrated analysis of the metabolic cars, public transport, etc.) and other variables such as distance cov- pattern must include other dimensions beyond energy: global and local ered. The analysis of the residential sector, carried out at the level of emissions, economic cost reduction, labor requirement, effects on citi- barrios, includes relevant factors affecting energy consumption, such as zens’ life quality, etc. Without considering all these dimensions, it is family income, housing area, multi-store index and year of construc- easy to fall into a trap of flawed monitoring schemes, where an un- tion. planned collapse in economic activity may be interpreted as a suc- In conclusion, the end-use matrix represents a promising analytical cessful environmental policy reducing emissions or where targets are tool for overcoming the limits of conventional quantitative analysis by: achieved through “externalization” of energy intensive activities (i) moving away from a mono-scale, mono-dimensional quantitative This work is a step toward establishing a comprehensive multi-level analysis toward a multi-scale multidimensional quantitative analysis; system of integrated accounting in the form of the end-use matrix to (ii) moving away from predicative representations (deterministic re- provide standards and guidance that will help local governments in sults) toward impredicative representations (contingent results); (iii) developing strategies toward reduction of emissions. Constituent com- Moving away from analytical models providing representations chosen ponents of the urban system and their size are defined using two fund by the analysts/experts, toward analytical tool-kits designed for co- coordinates: (i) human activity (residents, commuters and tourists); and production of information with the users of the analyses. Indeed, a 20 L. Pérez-Sánchez et al. Energy Policy 124 (2019) 13–22 meaningful analysis of urban energy metabolism must necessarily be for Units of Excellence (MDM-2015-0552). This work reflects only the based on a complex information space, linking diverse aspects at dif- authors' view; the funding agencies cannot be held responsible for any ferent scales and levels. 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