Urban Metabolism Literature Review2012 44 Fea

7/24/2019 Urban Metabolism Literature Review2012 44 Fea

1/28

1

Center for Sustainable Urban Systems

UCLA INSTITUTE OF THE ENVIRONMENT

URBAN METABOLISM LITERATURE

REVIEW

Winter 2012

Tisha HolmesStephanie Pincetl

Director Center for Sustainable Urban Systems


2/28

URBAN METABOLISM LITERATURE REVIEW

2

Introduction

Cities have expanded dramatically in size, density and complexity across the globe (Kaye et al.,

2006). This rapid expansion has been accompanied by increased energy flows of inputs and

outputs such as fuel, food, waste and electricity that enter, exit and/or accumulate within and

external of the city boundaries (Kennedy et al., 2007). Energy production and use whilesupporting human systems often also trigger a chain of negative environmental impacts. These

include pollution and alteration of land and water from extraction processes, loss of ecosystemsfrom power generation infrastructure and increased concentrations of air pollutants including

greenhouse gases (GHGs) as well as disruption of human settlements and negative impacts on

human health and economies. The linear nature of these urban energy flows increase the

vulnerability of cities, dependent on the hinterlands for supply and disposal of materials, andpose one of the largest challenges to sustainability (Girardet, 2004).

The intended and unintended consequences of policy decisions shape energy flows throughurban systems. Understanding the complex and often invisible set of interacting and

interdependent policy decisions and outcomes of energy use can provide opportunities foridentifying specific forces that shape a citys energy consumption and its consequences. UrbanMetabolism (UM) is a multi-disciplinary and integrated platform that examines material and

energy flows in cities as complex systems as they are shaped by various social, economic and

environmental forces. Similar to biological organisms and ecosystems, cities cycle and transform

incoming raw materials, food, water and fuel into physical structures, biomass and waste (Deckeret al., 2000). Factors such as urban structure, form, climate, quality and age of building stock,

urban vegetation and transportation technology can influence the rate of a citys metabolism

(Girardet, 1992). As the demands for higher inputs of materials and energy to sustain the growthof cities continue to increase, understanding the metabolism of cities becomes extremely

important for policy makers and decision makers. The UM framework provides a rigorous tool

for analyzing relevant energy pathways at different scales and can lead to the development ofmanagement systems that increase resource use efficiencies, recycling of wastes and

conservation of energy.

This literature review will survey the various conceptual and empirical studies associated with

performance systems-based research on urban flows. The review discusses the implications of

these studies to larger research and policy questions to highlight points of convergence as well as

areas of debate and opportunities for further research.

I.

Urban Metabolism Overview

Abel Wolman (1965) developed the urban metabolism (UM) concept as a method of analyzingcities and communities through the quantification of inputs water, food and fuel, outputs sewage, solid refuse and air pollutants and tracking their respective transformations and flows.

He identified the three pressing metabolic challenges faced by urban regions as water supply

management, sewage disposal and air pollution control. National data on water, food and fueluse, with production rates of sewage, waste and air pollutants were used to determine per capita

inflow and outflow rates for a hypothetical American city of one million people. Wolmans


3/28


4/28


4

common metric of environmental and economic values (Odum, 1996; Odum & Odum, 2006).

From an ecological energetic perspective, all flows of materials are regarded as energy flows

(Huang et al., 2006). Emergy analysis seeks to provide a common value basis to study theenergetic flows in the metabolism of socio-economic systems.

SolarEmergyis defined as the available solar energy used up directly and indirectly to make aproduct or service (Odum, 1996). Solar energy, deep Earth heat and tidal energy are major

energy inputs in the system.Emergyanalysis characterizes products and services in terms of the

amount of energy needed to do a particular task if solar radiation were the only input (Hau and

Bakshi, 2004). The behavior of energy as it flows through ecosystems follows two principles ofthermodynamics First Law: energy transforms to another form and is neither created nor

destroyed; Second law: in all processes of energy, some energy will be degraded in quality and

transformed into waste heat (Lin, 2006). Emergyanalysis is based on additional the MaximumEmpower Principle proposed by Lotka (1925) where successful systems are able to function

most effectively with the inflow of Emergy inputs by reinforcing productive processes and

overcoming resource limits through system organization (Brown & Herendeen, 1996) (for

example, more efficient processes or using renewable resources). Based on these principles,Odum designed a set of energy circuit symbols for describing the interactions of ecosystem

components through energetic flows (SeeFigure 1;Odum, 1983).

Figure 1. Energy circuit symbol: a) energy circuit; b) source; c) tank; d) heat sink; e) interaction; f) producer;

g)consumer; h)transaction; i) box. (Huang et al., 2006).

Solar transformity is an important concept in Emergy, defined as the Solar Emergy required tomake 1 joule of a service or product and is measured in solar Emergy joules per Joule (sej/J)

(Odum, 1996). Solar transformity () is calculated by dividing a products available energy (B)

by its Solar Emergy(M) or M = x B. Odum argued that the different types of energy flows areorganized in an energy transformation hierarchy (Odum, 1996). Thus, Transformity measures

energy quality and can be used to measure the Emergy of resources and products. Most case


5/28


5

studies utilize the Odums transformities calculations to calculate the Emergy of their inputs

(Hau & Bashki, 2004).

In theirEmergyanalysis of West Virginia, Campbell et al. (2004) outline the five main steps to

complete anEmergyevaluation as:

1)

Complete a detailed systems diagram representing all interactions, components, moneytransactions and energy flow pathways between human and natural components of the system

(SeeFigure 2).

Figure 2. An aggregated energy systems diagram of theEmergyresource base for the economy of West

Virginia.Emergyinflows and outflows include: renewable resource inflows (R), purchased resources fuel

(F), goods (G) and services (PI), exports of goods (B) and services (PE2+ PE3). Money flows on the dashed

lines (Is and Es) as a counter-current toEmergyin exchanges (diamond symbols). The System contains

interior storages of minerals (N3), water and soil (N0) and the lands and waters receiving (RR) and absorbing

(RA) renewable resources. The circulation of money, X, is as a money wheel, GSP, within the box representing

the states economy. (Campbell et al., 2005).

2) Translate variables into an aggregated diagram addressing specific pathways.

3) Translate pathways intoEmergyanalysis tables (SeeFigure 3).

Figure 3. Tabular format for anEmergyevaluation. Source: Campbell et al., (2005).

4) Gather raw data from government sources, needed to complete the Emergy analysis withTransformity conversion factors needed to change the raw data into Emery units


6/28


6

5) Calculate indices from subsets of data to compare systems, predict trends, and suggest

alternatives to improveEmergyefficiency through the system.

Emergy-based UM analyses have been conducted for specific cities including Zucchettos 1975

study of Miamis urban metabolism where economic, natural system and energy data were

compiled from 1950-1972. Huang, (1998), Huang & Hsu (2003) and Huang & Chen (2009)analyzed the Emergy flows of Taipei, Campbell et al.s (2005) evaluated West Virginia and

Zhang et al. (2009) focused on Beijing and 5 other large Chinese cities. Each study recognized

that the variation in the quality of different forms of energy and utilized a universal metric toproduce comprehensive comparisons overtime (e.g. See Huang & Chen, 2009) Emergy flow

comparison in Figure 4). The studies were driven by the premise that maximizing Emergy

production and use would lead to choices that maximize real wealth and public benefit.

Figure 4. MajorEmergyflows in the Taipei area. sej = solar equivalent joules. (Huang & Chen, 2009).

Huang & Chens (2009) updated analysis of Taipei demonstrated that Emergy flows are also

important for the calculation of Emergyindices to measure urban development and describe thevalue of material flows within the urban system (See Figure 5). Further evaluation of these

flows provides a preliminary understanding of the value and contribution of these materials to

the urban ecological-economic systems.


7/28


7

Figure 5.Emergy indexes. N = nonrenewable energy flows; F = importedEmergyflows; R = locally available

renewableEmergyflows; U = totalEmergyused by a process. (Huang & Chen, 2009).

Since its first emergence in 1983, the Emergy methodology has evolved and matured as new

research projects revealed new elements to explore. In addition to the analysis of cities, it hasbeen used to study ecosystems, information flows, agriculture, landscape development,ecological engineering and material recycling (Brown & Ulgiati, 2004). Huang et al.s (2006)

analysis of Taiwan attempted to extend material flow analysis to include energy flows and

incorporating Emergy evaluation to evaluate materials and energy through a common energybasis. After completing separate Emergy and Material Flow Analysis (MFA) for Taiwan and

comparing indicators of mass and Emergy, the research team found that MFA was not able to

identify Taiwans increasing dependence on energy use or the quality difference of materialconsumed. In contrast, they concluded that the Emergy concept can help systemize the

interrelations between society and the natural environment while analyzing energy flows.

Emergyanalysis was also seen as an important comparative tool for understanding the relative

work of other materials flowing through a socio-economic system (Huang et al., 2006).

Although the concept of Emergywas developed decades before the acceptance of more popular

methodologies such as MFA and Life Cycle Assessment (LCA),Emergyspecialists continue tomeet resistance in advancing Emergy as a conceptual framework for investigating the natural

ecosystems, human dominated systems and related processes. This is a result of the skepticism

around Emergy theory, underlying computations, its relationship with other thermodynamic


8/28


8

quantities, and the quantification of global energy flows into solar equivalents (Mnsson &

McGlade, 1993; Ayres, 1998; Cleveland et al., 2000; Hau & Bakshi, 2004).

Mass-Energy Flows and Urban Metabolism

One of the core ideas behind UM analysis is that materials enter (flow) and are used to build upbiophysical structures human bodies, artifacts, buildings, machines, tools, agricultural crops,

domestic animals and livestock in society (Haberl et al., 2001). Through the application of

energy, human societies transform raw materials and resources in an economic process to

provide material goods to meet demand needs (Huang et al., 2006). Before discussing theapplication of mass flow-based UM studies, a brief review of the main methodological tools used

Material Flow Analysis and Life Cycle Analysis as well as an assessment of each methods

strength and weaknesses is warranted.

Material Flow Analysis

The Material Flow Analysis (MFA) approach is widely used in UM analysis since metrics for the

assessment of urban materials, flows and stocks are available (Barles, 2007). Early MFAanalyses focused on identifying material flows at the national level (Wernick & Ausubel, 1995;

WRI, 2000; EUROSTAT, 2001). Countries such as Austria, Japan, Germany and Sweden have

also established material flow accounts (EUROSTAT, 2001). Material flows analysis provides aframework for analyzing the ways urban areas transform natural resources and is frequently used

in the engineering field, however emphasis is placed on the flow of a specific substance rather

than through entire systems (Baccini & Brunner, 1991).

The goal of the MFA is to provide a system level understanding of how a city, region or nation

functions. Data is represented in mass (e.g. tons) to measure the weights of material inflows andoutflows. Based on the principle of mass conversion where mass in = mass out + stock changes,

MFA measures the materials flowing into a system, the stocks and flows within it and the

resulting outputs from the system to other systems (Sahely et al., 2003). This tool aids decision-makers in analyzing material flows and stocks within a given system, evaluating the importance

and relevance of these flows and stocks and controlling material flows and stocks to achieve

management goals (Hendriks et al., 2000).

Baccini & Brunner (1991) outline the general methodological steps of urban metabolism using

Material Flow Analysis as follows:

1) Definition of goals and research questions of the study

2) System description Boundaries of space and time are defined and the relevant processes,

goods and substances are defined and linked. Indicator materials such as carbon, nitrogen andphosphorus are chosen based the nature of system.

3) Data acquisition Developed by measurements, market research, expert judgment, best

estimates, interviews and hands-on knowledge.

4) Material balances, dynamic mathematical modeling and scenario building Results can beintegrated into static or dynamic models to assess the impact of various decisions on specific

material stocks and flows


9/28


9

5) Interpretation Loading quantities, comparisons of results against environmental standards,

sustainability indicators or other assessment approaches are made.

MFA results can be benchmarked against environmental standards or interpreted using

assessment methodologies such as ecological footprint analysis (Wackernagel & Rees,1996).

Rees & Wackernagel (1996) examined the flow of materials and energy into and out of an urbanarea using a spatial ecological footprint analysis. The footprint expressed the amount of land

required to meet the citys metabolic needs. Their calculations were based on five major

categories of consumption food, housing, transportation, consumer goods and services. They

argue that consumption related human impacts reveal societal values or behaviors at acommunity and individual level. Giradet (1999) utilized MFA in an ecological footprint analysis

to calculate the resource use in greater London and estimated the regions ecological footprint as

125 times the area occupied. Similarly, Folke et al., (1997) estimated the ecological footprint of29 largest cities in Baltic Europe, the appropriation of global marine ecosystems for seafood

consumption and GHG emissions sequestration of global forest ecosystems. MFA has also been

heavily utilized in waste management and environmental assessments (Sahely et al., 2003).These

studies all demonstrated that the consumption of ecosystem outputs in the form of food, timberand ecosystem waste sinks for cities were magnitudes larger than the geographic area of cities.

MFA has been established as a standardized approach to evaluating the metabolism of materialflows at a national scale (EUROSTAT, 2001). It provides quantitative understanding of the finite

nature of resources available to sustain metabolic processes in urban systems and points to the

importance of including material resource management into policy analyses and discourses.Because MFA tries to simplify these complex relationships within a predefined socio-economic

system, many outflows and interactions within and between the natural environment and human

systems are omitted (Huang et al., 2006). Additionally, since the purpose of MFA is to providean overview of the system, it is necessary to aggregate material flows. This aggregation ignores

the specific identities of materials and can lead to inaccurate data outcomes, indicators and

policy decisions (Hau & Baski, 2004). Since MFAs focus is on materials, energetic aspects ofthe metabolism are not addressed limiting the scope and power of the approach in understanding

the UM of a system (Haberl, 2001). To address this gap, Haberl (2001) proposed a material-

energy flow accounting (MEFA) method to analyze energy flows that enter and leave a national

economy. However, the analysis is limited to an accounting exercise and does not assess therelative contribution of the flows nor address the external drivers (Huang et al., 2006).

Life-Cycle Assessment

Life-cycle assessment (LCA) is used to provide a cradle-to-grave assessment of a process or

larger system including direct, indirect, and supply chain effects and analyze the associated

environmental impacts from extraction to final disposal (Solli et al., 2002; Chester, 2010). TheInternational Standards Organization (ISO) defines LCA as the complication and evaluation of

the inputs, outputs and the potential environmental impacts of a product system throughout its

life cycle. It is a young field of research rooted in research related to energy requirements and

pollution prevention of the 1960s and 1970s (Rebitzer et al., 2004). The quantitative tool iswidely applied by various industries to measure and compare the life time environmental impacts

of materials and processes starting with the product design/development, followed by resource


10/28


10

extraction, production, use/consumption and end of life activities. (See Figure 6;Huang et al.,

2009; Techato, 2009).

Figure 6. Schematic representation of a generic life cycle of a product. (Rebitzer et al., 2004).

LCA also estimates and assesses the environmental impacts of a product through its life cyclesuch as climate change, stratospheric ozone depletion, troposheric ozone creation,

eutrophication, acidification, depletion of resources. The ISO 14040 standards direct almost all

applied work on LCA (Heijungs et al., 2009). The analysis begins with the development of alife-cycle inventory (LCI) where all environmental inputs and outputs from the life time of the

product or process are quantified and compiled. This is followed by a life cycle impact

assessment (LCIA) that presents results that enables comparisons or further analysis (SeeFigure

7;Huang et al., 2009).


11/28


11

Figure 7. Framework of life cycle assessment. (Huang et al., 2009).

Process LCA and Economic Input-Output (EIO) LCA are the two primary approaches for

performing an LCA study. Process-based LCA evaluates the direct component of interest,considering the inputs, outputs and sub-processes moving up the supply chain (Chester, 2010). It

is the most common approach and requires significant data and resource inputs, thus limiting the

ability to evaluate the entire supply chain (Hendrickson, 2006; Chester, 2010). The EIO-LCAapproach evaluates the resource inputs and emissions outputs associated with economic activity

in every sector of the economy (Chester, 2010). These approaches have also been combined to

reduce data and resource constraints in modeling while capturing the entire supply chain(Chester, 2010). Data is derived generally from a mix of sources and are subject to differences in

quality.

Cities have not historically been major units of analysis in Industrial Ecology, however LCA isgaining importance as an analytical tool in assessing of the overall environmental impact of

urban activities (Bai 2007). LCAs have been executed for energy, materials, water, nutrients and

waste footprints of cities (Chester, 2010). Huang et al. (2009) used LCA to measure and comparethe key environmental loadings from a road during its lifetime. The results provided decision

makers with a method of quantifying the impacts of road maintenance work and projects.

Heijung et al. (2009) examine life cycle assessments for sustainability, noting that the scope ofLCA is limited to environmental questions, while sustainability is much broader. They combine

the two concepts into a life cycle sustainability analysis (LCSA). This framework provides an

integrated way of evaluating economic, social and environmental impacts that are not covered by

present day LCA.

LCA is a consistent tool that can quantify all possible environmental burdens in relation to a

functional unit. Its attention to system boundaries and capturing direct and indirect effects ofsupply chains effects can also help fill the gaps of the MFA approach and offers critical insight

into upstream components that may dominate the footprint of the city as well as the interrelated

components of the urban system (Chester, 2010). In determining the flows and processes withinthe urban system, a great deal of data is needed to compile complex system-wide models of

resource flows that increase the analytical power. However the tool still requires greater spatial

and temporal resolution, improved non-linear modeling capabilities and greater consideration ofsocio-economic dimensions of urban environmental impacts (Udo de Haes et al., 2004).

Mass-Energy Flow UM Studies

The engineering approach was advanced in early studies by Hanya & Ambe (1974) for Tokyo,Duvigneaud & Denayeyer-De Smet (1975) for Brussels, including a comprehensive

quantification of the natural energy balance (SeeFigure 8.), and Newcombe et al. (1978) who

developed an energy analysis of construction materials and input-output of manufacturedproducts for Hong Kong.


12/28


12

Figure 8. The urban metabolism of Brussels, Belgium in the early 1970s. Source: Duvigneaud and Denaeyer-

De Smet 1977.

In the early 1970s, the concept of examining material flows for Urban Metabolism analysis wasformally incorporated as part of the UNESCO Division of Ecological Science Man and

Biosphere (MAB) program (Pomzi & Szab, 2009). This program aimed to support integrated

and multidisciplinary research into the sustainable use of resources, biodiversity conservationand problems of urban ecosystems (Bonnes et al., 2004). The main element of the MAB is its

ecosystem approach that aims to integrate the study of natural and human/social processes of

ecosystems and their inter-relationships. Applied in over 105 countries, the MABs main lines ofaction are threefold: 1) Minimizing biodiversity loss through research and capacity-building for

ecosystem management; 2) Biosphere reserves as a means of promoting environmental

sustainability and 3) Enhancing linkages between cultural and biological diversity (UNESCO,

2010).

During the 1990s, research in the field of UM received moderate attention with the increased

sophistication of methodological tools like MFA. Baccini and Brunner (1991) used the MFA

approach to understand the metabolism of the anthroposhere of the - the subsystem of theenvironment in which humans interact and reported stocks and flows of resources in terms of

mass (See Figure 9). In 1993, the international symposium on urban metabolism was held inKobe Japan without many publications (Kennedy, 2010). Bohel (1994) considered the use on an

UM framework to managing food systems in developing countries and was critical of its

application. In 1996, Newman and his colleagues studied the increasing trends of per capitaresource input and waste metabolism of Sydney for the State of Environment report on Australia

between 1970 and 1990. This report, followed by subsequent annual accounting reports, was the


13/28


13

first independent nation-wide assessment on the state of Australias environment developed to

aid decision makers in government, industry and community groups (State of the Environment

Advisory Council, 1996).

Figure 9. The anthroposphere: inputs and outputs. Source: Hendriks et al. (2000).

Newmans study of Australia identified larger cities as more sustainable in terms of per capitause of resources and livability utilizing such indicators as income, education, housing and

accessibility. However, these cities were also more likely to reach unsustainable carryingcapacity limits, within increasing metabolic flows and livability deterioration from the core to thefringe suburbs (Newman et al., 1996; Newman, 1999). Additionally, ex-urban and coastal

settlements are the least sustainable of all developments and rural settlements had the lowest

metabolic flows and livability measures. Newman (1999) extended the urban metabolism modelto address sustainability goals by including the dynamics of settlements and livability in these

settlements. Newman defined the physical, biological and human bases of the city and integrated

economic and social aspects of sustainability with the environment (seeFigure 10). He applied

this extended model of assessing metabolic flows and livability to a range of human activities inindustrial areas, households and neighborhoods, urban demonstration projects and for city

comparisons (SeeFigure 11;Newman, 1999).


14/28


14

Figure 10. Extended metabolism model of human settlements. (Newman, 1999).


15/28


15

Figure 11. Indicators of sustainability. (Newman, 1999).

As the environmental stresses engendered by cities continued to increase with the expansion ofurban populations, there was a resurgence of UM studies in at the turn of the century (Kennedy,

2010). The research community began to build upon the data and findings of previous UM

studies for various cities. Hendriks et al. (2000) used similar approaches to analyze Vienna andthe Swiss Lowlands. Building on the 1978 work of Newcombe et al., Warren-Rhodes & Koenig

(2001) studied further the metabolism of Hong Kong. Their work described increasing


16/28


16

environmental impacts with the transition from a manufacturing to a service based economy.

Not only did Hong Kong add over 3 million people between 1971 and 1997, but additionally

Warren-Rhodes and Koenig revealed that Hong Kongs increased wealth correlated with higherconsumption rates of food (20% over 1971 values), water (40% over 1971 values) and materials

(149% over 1971 values) per capita. Total air emissions, carbon dioxide outputs, municipal solid

wastes and sewage discharges increased by 30%, 250%, 245% and 253% respectively (Warren-Rhodes & Koeing, 2001).

More recently, the quantification of the urban metabolism of several cities has been conducted.

In Decker et al.s (2000) extensive review of the energy and material flows through the worlds25 largest cities, researchers found that water fluxes comprised 90% of all material entering the

system and proved to be the most dominant flux across the megacities. As a result, changes in

water infrastructure will be necessary to manage increasing water demand. The study alsoinvestigated gross food consumption and indicated that although limited information is available,

the flow of food is likely to have an impact on nitrogen cycles in supplying agricultural areas and

solid waste accumulation in the city. They also compared fuel flows among cities and revealed

large variations in fuel type and quantity resulting in an overall degradation of ecosystems due totechnological development (such as roads and fuel distribution infrastructure) and fossil fuel use.

The review presents an interesting scenario; modern megacities will achieve climax states whenglobal energy sources are maximally utilized, energy fluxes are at a steady state and

infrastructure growth has ceased. They argue that in pre-modern times, cities approached a

steady climax state since they were dependent on localized and renewable energy, food andtransportation networks which limited the extent of dependence on the hinterland for resources

and waste disposal. Conversely, current earth system level succession patterns in urban areas

show an increase their use of urban energy and material flows as development continues. Thus,analyzing the urban metabolism and subsequent succession stages of material and energy fluxes

at the regional scale over time is critical to determining the structure and function of climax

systems based on more local and renewable resource streams. It also provides opportunities forinsuring system stability and persistence through the management of infrastructure and efficient

recycling of waste flows (Decker et al., 2000).

The urban metabolism analysis of Greater Toronto by Sahely et al. (2003) identified an increaseof the rate of inputs and outputs over 12 years from 1987 to 1999. Inputs of water and electricity

were estimated to increase marginally less than the rate of population growth. With the exception

of diesel fuel, inputs of gasoline and food increased by marginally greater percentages than thepopulation. All measured output parameters except CO2emissions, are increasing more slowly

than the population. Comparisons were also made between the metabolic flows of Greater

Toronto with Hong Kong (see Figure 12). The study attributed increased efficiency ofmetabolism parameters to enlightened policy, wise investments, increased recycling and

improvements in infrastructure. They propose further research into the economic drivers of UM

and the integration of the UM findings into a macroeconomic model of the Greater Toronto

Area.


17/28


17

Figure 12. Comparison of urban metabolism a) the GTA 1999 and b) Hong Kong 1997. Food, water,

wastewater and residential solid waste in tonnes per capita, CO2and BOD5in kilograms per capita and

electricity in megajoules per capita. (Sahely et al., 2003).

Although the rationale for selection is not explicitly addressed in the literature, there is a great

deal of variation in the scales of analysis in UM studies. Some studies have used the UM

framework to analyze specific elements at the micro-scale within an urban region. Burstrm etal. (1997) and Faerge et al. (2001) studied flows of nitrogen (N) and phosphorous (P) in Bangkok

and Stockholm respectively. Burstrm et al. (1997) presented a comprehensive picture of the

citys metabolism of the two elements in one year (1995) using MFA to support the development

of local nutrient management policies. The study identified dominant pathways for N and P asimport food supply households waste management, however the fate of the elements

after waste management differ (Burstrm et al., 1997). The most important sources and sinks forN were food consumption in private households and restaurants resulting in large emissions towater, N emissions from transportation sector through combustion of fossil fuels, discharges

from industrial combustion engines and machines and the energy supply sector when converting

N in fuels to inert gas. For P, the most significant pathways were through food consumption andthe resulting municipal sludge and the service sector via import of P in detergents that end up in

sewage sludge. Similarly, Faerge et al. (2001) developed a nutrient balance model to understand

urban nutrient flows and explore the potential for nutrient recycling to agriculture in the face of


18/28


18

mismanagement organic waste and urban development. They discovered that only a small

fraction of urban N (7%) and P (9%) are recovered from the total food supply. Most of the loss

of both nutrient flows occurred to the central Chao Phraya River where elevated levels weredetected. They concluded that in and outflows of N are almost in balance, but large amounts of P

accumulate within the metropolitan area. Faerge et al. also identify that organic waste from

Bangkok that is discharged into the rivers and oceans are heavily loaded with plant nutrients.Analyzing urban flows at this scale enabled both research terms to identify the most significant

points of nutrient loss and identify where recovery and reuse efforts can be directed to close the

metabolic loop.

Other studies approached the evaluation of several material and energy flows at a city-scale or

regional level such as (Emmenegger et al.s (2003)) analysis of Geneva, Ngo and Patakis (2008)

study of Los Angeles County and Barles (2007 and 2009) evaluation of Paris. In her analysis ofthe UM of Paris and its region, Barles selected MFA to analyze flows at multiple scales local,

city and region demonstrating that Paris is dependent on a wider area for its materials and on

the suburbs and region for its waste treatment. Barles also proposed linking MFA to socio-

ecological conditions that drive material flows and their evolution in order to develop a holisticunderstanding of urban systems (Barles ,2007).

Ngo and Pataki (2008) identified a decline in inputs of resources and outputs of pollution on aper capita basis from 1990 to 2000 for all materials except food imports and wastewater outputs.

They compare metabolisms in Los Angeles to 8 other urban regions and demonstrate that per

capita food imports, water imports and energy imports are generally higher, while outputs ofwaste and greenhouse gas emissions were comparable or lower. Additionally, total per capita

energy consumption, especially in the transportation sector and total water imports were quite

high in comparison to other cities (SeeFigure 13).

Figure 13. Comparison of urban mass and energy balances between Ngo and Pataki (2008) study of Los

Angeles County and previous studies since 1990 as compiled by Kennedy et al. (2007). (Ngo and Pataki 2008).


19/28


19

Ngo and Pataki attribute the successful decrease in some inputs to improved local efficiency and

reduction management policies. They also highlight the water out flows as a critical area of

future research since evapo-transpiration and runoff losses are not recovered or reused for watersupply. There is also a great potential for increases in residential per capita energy consumption

due to increased demand, consumer behaviors and/or warming climates which needs to be

addressed (Ngo & Pataki, 2008).

Researchers have also begun to extend the UM framework beyond the city-region unit of

analysis to inform related aspects of the urban sustainability. In the field of urban design in

particular, using UM context is a relatively new development that serves as a descriptiveframework to the visioning process of more sustainable communities and cities. Oswald and

Baccini (2003; 2008) demonstrate how a combination of morphological and physiological tools

can be used in the reconstruction of the city. They provide four principles for redesigning cities:shapability; sustainability; reconstruction; and responsibility. The four major urban activities: to

nourish and recover; to clean; to reside and work; and to transport and communicate, as

identified by Baccini & Brunner (1991). Together they are assessed in terms of four major

components of urban metabolism: water, food (biomass), construction materials, and energy(Oswald & Baccini, 2008; Kennedy, 2010). Professor John Fernandez and students in MITs

School of Architecture have used the perspective of urban metabolism in the re-design of New

Orleans post-Hurricane Katrina, using MFA to produce more ecologically sensitive designs(Quinn, 2008). Students in Civil Engineering at the University of Toronto also used UM as a tool

to guide the study of sustainable design infrastructure for Toronto (Kennedy, 2010). The students

evaluated design challenges typically at the neighborhood scale, which involve integration ofvarious infrastructure using the concept of neighborhood metabolism (Codoban & Kennedy,

2008; Engel-Yan et al., 2005). Thus the UM framework can serve as a complimentary tool that

can inform the design and decision-making process. By tracing the flows of water, energy,nutrients and materials through an urban system, communities and cities can be designed in way

that may close identified metabolic loops, since critical leverage points and flows that threaten

system sustainability would have been isolated.

Summary

An urban systems metabolism can be examined by looking at energy flows or more broadly to

include flows of water, materials and nutrients to develop a quantified understanding of theinputs that support urban systems and the wastes generated by city processes. Academics and

researchers have utilized the urban metabolism framework to analyze different urban areas and

system components for over forty years (See FigureFigure 14;Kennedy, 2010). The ability toquantify material and energy flows has led to a diversification in the application of UM analyses

in a variety of research questions over time. Quantification of tangible flows in mass, dollars orEmergy fluxes can provide a description of the main components and interrelationships thatmake up a citys metabolism. The generic units used in most urban metabolism studies are in

joules per unit time and material and water balances in mass (grams or kilograms) per unit time

(Baccini & Brunner, 1991; Hendriks et al., 2000; Sahely et al., 2003), while other researchers

continue to advance solar emergy joules (seJ) as a more comprehensive and universal metric(Odum, 1996; Huang, 1998; Huang & Hsu, 2003; Huang & Chen, 2009). Researchers face the

challenges of inadequate or disparate data as well as difficulties of comparing materials and

energy represented in different units. Additionally, qualitative assessments such social or


20/28


20

sustainability indices, comparative usefulness of materials and valuation of ecosystem services

and disservices are limited in these types of models. Although these models address the flows

between the economy and environment, the relationships between the elements at vertical andhorizontal scales also require further exploration.

Current studies of urban metabolism from both an ecological and engineering perspective havemade a link between UM and sustainability through the use of indicators and policy analysis. A

consistent finding in these studies is that the urban metabolism of cities is increasing. This points

to the need to better characterize the amount of materials stored as stock within the urban system

buildings, roads, infrastructure -- and the flows into cities and out of them more broadly, sincestudies have been conducted on only a limited number of cities worldwide (Kennedy et al.,

2007). As the inputs in most cities outweigh the outputs, there is a resulting growth in the

material stock remaining within the system. Quantifying the present stock becomes important forfuture flows out of the city as well as the long-term stability of the entire urban system (Brunner,

2007).

Figure 14. Chronological review table of UM studies. (Kennedy et al. 2010).


21/28


21


22/28


22

II.

Discussion

UM studies clearly demonstrate an increase in the rates of metabolism in cities throughout the

world (Kennedy et al. 2007). Large increases in material and energy flows of food-wastestreams, imports, solid-waste accumulation, paper, plastics and building materials from areas

outside the boundaries of the urban system keep the metabolic cycles in cities open. (Grimm et

al., 2008). Brunner (2007) categorizes cities as linear reactors whose metabolism remains openand vulnerable depending on the hinterlands for material supply and disposal. In essence, the

linear pattern of production, consumption and disposal is different than natures circular

metabolism (Huang & Hsu, 2003). Additionally, the inputs outweigh the outputs resulting in a

growth of the material stock in urban areas which becomes significant for future flows andpathways to sustainability.

Studies have examined altering the design and urban form of cities to close the metabolism loop

and to improve the characteristics of a citys flows. Barriers to closing this loop range fromsignificantly altering behaviors and attitudes to changing various processes within the urban

system. By designing cities that are less energy intensive and dependent on resources producedbeyond their boundaries, city and regional governments would be better positioned to manage

material and energy outflows. From an urban ecology perspective, cities are considered

unsustainable systems given their continuous dependence on material and energy imports and theexports of waste (Camagni et al., 1998). Thus the sustainability of cities is heavily dependent on

the ability of the surrounding environment to provide the required resources and environmental


23/28


23

services (Huang & Chen, 2009). Since the methodological tools do not adequately incorporate

considerations of ecosystem services, developing indicators and metrics of supporting, regulating

and provisioning ecosystem services to include in the UM framework is an important researchpriority (Pataki, 2010).

Using the urban metabolism framework will also create an accounting inventory of the actualand embedded energy used and its associated impacts in urban systems over short and long-term

time scales. This will enable a more complete consideration of the full economic, environmental

and social effects of energy use that will inform better policy-making decisions. By revealing the

intended and unintended consequences of policy decisions, identification of critical leveragepoints of change can be made. Additionally, quantified metabolisms and indicators can

complement further research into the nature of funding for urban management programs, the

manner in which it is disbursed and the identification of the specific actors receiving allotments.

Standardized methods used to quantify the flows through urban areas enable comparisons and

projections of future scenarios. The two major approaches emergy and material flows

(including quantitative analyses of life cycle costs, material flows and economic valuation) differin information, calculation and metrics used. The variation in the units of analysis and metrics

may prove a challenge in comparing different results of urban metabolisms between city-regions,

countries as well as over time and across different spatial scales. However, the diversity ofmetrics can also contribute to more robust modeling tools that combine the strengths of each

method.

UMs results contribute important parameters that provide criteria for sustainability indicators

(Maclaren, 1996). Political, demographic, economic and geographic factors directly influence

innovation and development of effective sustainable policies. Investigating the scales ofgovernance and institutional rules and conventions that undergird current urban systems is

critical in understanding path dependencies and critical policy changes necessary to reduce

impacts. However data availability and accuracy at the city level continues to be a majorlimitation, and little work has been done connecting flows to policy frameworks at multiple

scales, from the local to the international. By conducting cross-cutting field research and data

analysis, the outcomes of UM research will be more accurate and useful.

Most system level research has explored the nature of multi-scale approaches; however it is

important to understand the interconnections and interrelations between and across scales

(Bunnell & Coe, 2001). Urban centers grow in complex ways due to dynamic and interlinkedgeographical and institutional forces converging upon them (Grimm et al., 2008). Cities are now

dependent on access to resources and ecosystem functions outside of their administrative

boundaries. Folke et al. (1997) and Rydin & Moore (2009) highlight European cities asembedded in a web of connections that link ecosystems and countries across all scales of space

and time revealing that boundaries of cities have become quite porous as a result of globalization

in trade, information and communication networks. Thus, focusing on one spatial scale prevents

the adequate analysis of all processes occurring within a system and can lead to unintendedeffects. Given the heterogeneous nature of urban systems, the scale at which UM analysis is

performed can influence the modeling results, comparative outcomes and subsequent policy

decisions.


24/28


24

At present, UM studies focus on the biophysical environment without addressing the social and

institutional drivers behind these flows and outcomes. Data gaps, omitted/hidden flows,uncertainty regarding the appropriate scale of analysis and segregated information sources

continue to influence the comprehensive validity of assessments of overall urban energy use and

related policy decisions. Collaboration and open communication across sectors and researchcenters working on sustainable energy problems is also critical for developing a comprehensive

pool of information that is accessible to various users and end types.

III. Conclusion

This review of the UM literature provides a general introduction to the various considerations

involved with developing an integrated approach and to understanding the complex dimensions

of energy-use in urban systems. UM is a quantitative framework that enables policy-makers andpractitioners to identify early trends, set priorities, develop indicators and establish policy

directives. UM has become an integral part in the analysis of the state of environment reporting

in Europe, and is gradually finding acceptance in other places. It provides information aboutenergy efficiency, material cycling, waste management and infrastructure in urban systems(Newman et al., 1996; Sahely et al., 2003) and is an important tool to understanding energy use

in communities.

Emergy analysis, Material Flow Analysis and Life Cycle Assessment are methodologies that

attempt to quantify flows of material and energy in complex systems at multiple scales, and can

be incorporate into the urban metabolism framework. These different approaches will need to bebetter synthesized such that more consistency is achieved across cities and nations. UM points

out, first and foremost, the significant amounts of energy embedded in materials (including their

life cycle), and the energy used in urban activities and the waste energy. This emphasis and data

can help policy makers better understand energy used by society and cities. This should helppolicy makers better develop strategies to reduce energy use. Secondly, UM energy analyses

will provide a rigorous data set from which a better understanding of the sources of GHGs will

be developed, and the GHG emissions themselves. To date GHGs tend to be quantified inisolation from energy use, from the generative structure of the GHGs.

However, further research is needed to understand the drivers of energy use such as economicpolicy, institutional rules that guide urban development, and environmental protection.

Synthesizing UM with its social/economic and political policy underpinnings is the next research

frontier.

Literature Cited

Baccini, P., & Brunner, P. H. (1991). Metabolism of the anthroposphere. Berlin; New York:Springer-Verlag.

Baccini, P., & Oswald, F. (2008). Designing the urban: Linking physiology and morphology. In

G. H. e. a. Hadorn (Ed.),Handbook of Transdisciplinary Research: Springer Netherlands.


25/28


25

Barles, S. (2007). A material flow analysis of Paris and its region. Paper presented at the

International Conference CISBAT.

Barles, S. (2009). Urban metabolism of Paris and its region.Journal of Industrial Ecology, 13(6),898-913.

BONNES, M., CARRUS, G., BONAIUTO, M., FORNARA, F., & PASSAFARO, P. (2004).

Inhabitants' Environmental Perceptions in the City of Rome within the Framework forUrban Biosphere Reserves of the UNESCO Programme on Man and

Biospherea. Annals of the New York Academy of Sciences, 1023(Urban

Biosphere and Society: Partnership of Cities), 175-186.

Brown, M. T., & Herendeen, R. A. (1996). Embodied energy analysis and EMERGY analysis: acomparative view. [doi: DOI: 10.1016/S0921-8009(96)00046-8]. Ecological Economics,

19(3), 219-235.

Brunner, P. H. (2007). Reshaping urban metabolism.Journal of Industrial Ecology, 11(2), 11-13.Bunnell, T. G., & Coe, N. M. (2001). Spaces and scales of innovation. Progress in Human

Geography, 25(4), 569-589.

Camagni, R., Capello, R., & Nijkamp, P. (1998). Towards sustainable city policy: an economy-

environment technology nexus. [doi: DOI: 10.1016/S0921-8009(97)00032-3].EcologicalEconomics, 24(1), 103-118.

Campbell, D., Brandt-Williams, S. L., & Meisch, M. E. A. (2005). Environmental accountingusing Emergy: Evaluation of the State of West Virginia.

Campbell, D., Meisch, M., Demoss, T., Pomponio, J., & Bradley, P. M. (2004). Keeping the

books for environmental systems: An Emergy analysis of West Virginia.EnvironmentalMonitoring and Assessment, 94, 217-230.

Chester, M. (2010). Environmental Life-Cycle Assessment and Urban Sustainability. University

of California.

Decker, E. H., Elliott, S., Smith, F. A., Blake, D. R., & Rowland, F. S. (2000). Energy andmaterial flow through the urban ecosystem. Annual Review of Energy and the

Environment, 25, 685-740.

Duvigneaud, P., & Denaeyeyer-De Smet, S. (1975). L'Ecosysteme Urbs. L'Ecosysteme UrbainBruxellois. In P. Duvigneaud & P. Kestemont (Eds.), Productivite biologique en Belgique

(pp. 581-597). Bruxelles.

Emmenegger, M. F., & Frischknecht, R. (2003). Metabolisme du canton de Geneve. Phase I.

Uster: ESU Service.Engel-Yan, J., Kennedy, C., Saiz, S., & Pressnail, K. (2005). Toward sustainable

neighbourhoods: the need to consider infrastructure interactions. Canadian Journal ofCivil Engineering, 32(1), 45-57.

EUROSTAT. (2001). Economy-wide material flow accounts and derived indicators: A

methodological guide. Luxembourg.

Faerge, J., Magid, J., & Penning de Vries, F. W. T. (2001). Urban nutrient balance for Bangkok.Ecological Modelling, 139, 63-74.

Folke, C., Jansson, Larsson, J., & Costanza, R. (1997). Ecosystem appropriation by cities.

Ambio, 167-172.

Girardet, H. (1992). The Gaia atlas of cities. London: Gaia Books.Girardet, H. (2004). The metabolism of cities. In S. M. Wheeler & T. Beatley (Eds.), The

sustainable urban development reader. London, New York, Canada: Routledge.


26/28


26

Grimm, N. B., Faeth, S. H., Golubiewski, N. E., Redman, C. L., Wu, J., Bai, X., et al. (2008).

Global change and the ecology of cities. Science, 319, 756-760.

Haberl, H., Erb, K.-H., & Krausmann, F. (2001). How to calculate and interpret ecologicalfootprints for long periods of time: the case of Austria 1926-1995. [doi: DOI:

10.1016/S0921-8009(01)00152-5].Ecological Economics, 38(1), 25-45.

Haberl, H., Fischer-Kowalski, M., Krausmann, F., Weisz, H., & Winiwarter, V. (2004). Progresstowards sustainability? What the conceptual framework of material and energy flow

accounting (MEFA) can offer. [doi: DOI: 10.1016/j.landusepol.2003.10.013]. Land Use

Policy, 21(3), 199-213.

Hanya, T., & Ambe, Y. (1976). A study on the metabolism of cities. Paper presented at theScience for a better environment.

Hau, J. L., & Bakshi, B. R. (2004). Promise and problems of emergy analysis. EcologicalModelling, 178(1-2), 215-225.

Heijungs, R., Huppes, G., & Guinee, J. B. (2009). Life cycle assessment and sustainability

analysis of productrs, materials and technologies. Toward a scientific framework for

sustainability life cycle analysis. Polymer Degradation and Stability (In Press).

Hendrickson, C. T., Lave, L. B., & Matthews, H. S. (2006).Environmental life cycle assessmentof goods and services: An input-output approach. Washington, DC: RFF Press Book.

Hendriks, C., Obernosterer, R., Mller, D., Kytzia, S., Baccini, P., & Brunner, P. H. (2000).

Material Flow Analysis: a tool to support environmental policy decision making. Case-studies on the city of Vienna and the Swiss lowlands. Local Environment: The

International Journal of Justice and Sustainability, 5(3), 311 - 328.

Huang, S.-L. (1998). Urban ecosystems, energetic hierarchies, and ecological economics ofTaipei metropolis. [doi: DOI: 10.1006/jema.1997.0157]. Journal of Environmental

Management, 52(1), 39-51.

Huang, S.-L., Lee, C.-L., & Chen, C.-W. (2006). Socioeconomic metabolism in Taiwan: Emergysynthesis versus material flow analysis. [doi: DOI: 10.1016/j.resconrec.2006.01.005].

Resources, Conservation and Recycling, 48(2), 166-196.

Huang, S., & Hsu, W. (2003). Materials flow analysis and emergy evaluation of Taipei's urbanconstruction.Landscape and Urban Planning, 63(2), 61-74.

Huang, S. L., & Chen, C. W. (2009). Urbanization and Socioeconomic Metabolism in Taipei.

[Article].Journal of Industrial Ecology, 13(1), 75-93.

Kaye, J. P., Groffman, P. M., Grimm, N. B., Baker, L. A., & Pouyat, R. V. (2006). A distincturban biogeochemistry? [doi: DOI: 10.1016/j.tree.2005.12.006]. Trends in Ecology &

Evolution, 21(4), 192-199.

Kennedy, C. (2010). Urban metabolism: Metrics, applications and a framework for research.University of Toronto.

Kennedy, C., & Codoban, N. (2008). Metabolism of Neighborhoods.Journal of Urban Planningand Development, 134(1), 21-31.

Kennedy, C., Cuddihy, J., & Engel-Yan, J. (2007). The changing metabolism of cities.Journal of

Industrial Ecology, 11(2), 43-59.

Lin, P. L. (2006). Urban resilience: Energetic principles and a systems ecology approach.

Graduate Institute of Urban Planning, National Taipei University.Lotka, A. J. (1925).Elements of physical biology. Baltimore: Williams and Wilkins.

Maclaren, V. W. (1996). Urban Sustainability Reporting. Journal of the American PlanningAssociation, 62(2), 184 - 202.


27/28


27

Mansson, B. A., & McGlade, J. M. (1993). Ecology, thermodynamics and H.T. Odum's

conjectures. Oecologia, 93(4), 582-596.

Newcombe, K., Kalma, J. D., & Aston, A. R. (1978). The Metabolism of a City: The Case ofHong Kong.Ambio, 7(1), 3-15.

Newman, P. W. G. (1999). Sustainability and cities: extending the metabolism model. [doi: DOI:

10.1016/S0169-2046(99)00009-2].Landscape and Urban Planning, 44(4), 219-226.Newman, P. W. G., Birrell, B., Holmes, D., Mathers, C., Newton, P., Oakley, G., et al. (1996).

Chapter 3 - Human Settlements.

Ngo, N. S., & Pataki, D. E. (2008). The energy and mass balance of Los Angeles County. UrbanEcosystems, 11, 121-139.

Odum, H. T. (1983). Systems ecology: an introduction. New York: John Wiley & Sons, Inc.

Odum, H. T. (1996).Environmental accounting: EMERGY and environmental decision making.

New York: John Wiley & Sons, Inc.Odum, H. T. (1998). EMERGY evaluation. Paper presented at the International Workshop on

Advances in Energy Studies: Energy flows in ecology and economy.

Odum, H. T., & Odum, E. C. (2006). The prosperous way down. [doi: DOI:

10.1016/j.energy.2004.05.012].Energy, 31(1), 21-32.Oswald, F., Baccini, P., & Michaeili, M. (2003).Netzstadt: designing the urban: Birkhauser.

Pataki, D. E. (2010). Integrating ecosystem services into the urban metabolism framework.

University of California.Quinn, D. J. (2008). Modeling the resource consumption of housing in New Orleans using

System Dynamics.Massachusetts Institute of Technology, Boston.

Rebitzer, G., Ekvall, T., Frischknecht, R., Hunkeler, D., Norris, G., Rydberg, T., et al. (2004).Life cycle assessment: Part 1: Framework, goal and scope definition, inventory analysis,

and applications. [doi: DOI: 10.1016/j.envint.2003.11.005]. Environment International,30(5), 701-720.

Rydin, Y., & Moore, S. (2009). Sustainable construction and policy learning. In I. Cooper & M.

Symes (Eds.), Sustainable urban development, Volume 4: Changing professional

practice. Abingdon; New York: Routledge.Sahely, H., Dudding, S., & Kennedy, C. (2003). Estimating the urban metabolism of Canadian

cities: Greater Toronto Area case study. Canadian Journal of Civil Engineering, 30(2),

468-483.

Solli, C., Reenaas, M., Stromman, A. H., & Hertwich, E. G. (2009). Life cycle assessment ofwood-based heating in Norway.International Journal of Life Cycle Assessment, 14(517-

528).

Techato, K.-a., Watts, D. J., & Chaiprapat, S. (2009). Life cycle analysis of retrofitting with highenergy efficiency air-conditioner and fluorescent lamp in existing buildings. [doi: DOI:

10.1016/j.enpol.2008.08.021].Energy Policy, 37(1), 318-325.

Udo de Haes, H., Heijungs, R., Suh, S., & Huppes, G. (2004). Three strategies to overcome thelimitations of life-cycle assessment.Journal of Industrial Ecology, 8(3), 19-32.

UNESCO. (2010). People, Biodiversity & Ecology: The MAB Programme in Latin America and

the Caribbean Region. from http://portal.unesco.org/science/en/ev.php-

URL_ID=4793&URL_DO=DO_TOPIC&URL_SECTION=201.htmlWarren-Rhodes, K., & Koenig, A. (2001). Escalating trends in the Urban Metabolism of Hong

Kong_1971-1997.Ambio, 30(7), 429-438.
http://portal.unesco.org/science/en/ev.php-URL_ID=4793&URL_DO=DO_TOPIC&URL_SECTION=201.htmlhttp://portal.unesco.org/science/en/ev.php-URL_ID=4793&URL_DO=DO_TOPIC&URL_SECTION=201.htmlhttp://portal.unesco.org/science/en/ev.php-URL_ID=4793&URL_DO=DO_TOPIC&URL_SECTION=201.htmlhttp://portal.unesco.org/science/en/ev.php-URL_ID=4793&URL_DO=DO_TOPIC&URL_SECTION=201.html


28/28


Wernick, I. K., & Ausubel, J. H. (1995). National Materials Flows and the Environment. Annual

Review of Energy and the Environment, 20(1), 463-492.

Wolman, A. (1965). The metabolism of cities. Scientific American, 213(3), 178-193.WRI. (2000). The weight of nations: Material outflows from industrial economies. Washington,

DC.

Zhang, Y., Zhao, Y. W., Yang, Z. F., Chen, B., & Chen, G. Q. (2009). Measurement andevaluation of the metabolic capacity of an urban ecosystem. [doi: DOI:

10.1016/j.cnsns.2008.03.017]. Communications in Nonlinear Science and Numerical

Simulation, 14(4), 1758-1765.

Zucchetto, J. (1975). Energy-economic theory and mathematical models for combining thesystems of man and nature, case study: The urban region of Miami, Florida. [doi: DOI:

10.1016/0304-3800(75)90010-1].Ecological Modelling, 1(4), 241-268.

Documents

Urban Metabolism Literature Review2012 44 Fea