The 20th century was characterised by rapid and often uncontrolled urban growth leading to the emergence of huge dispersed or decompacted cities unlike the more compact cities of the 19th century. Fast industrialisation, new technological inventions such as automobiles, and the availability of cheap land and inexpensive fossil fuels were some of the driving forces of this model of urban development [1
] (pp. 243–266).
This dispersed urban model was heavily dependent on the automobile and the use of fossil fuels. An extensive build-up of transport and other infrastructures contributed to the deterioration of urban environmental performance in many cities globally through increased city footprints and impermeable surfaces; destruction of urban natural resources and green fields; reduced water quality and quantity; increased journey time, traffic congestion, and fuel consumption; and more [2
The consequences of this car-dependent dispersed city prompted academics and urban managers to search for innovative ways to promote economic and urban growth with less environmental impact and use of natural resources. Several reports, concepts, theories and methods addressing this issue were and are being produced.
In the 1980s, the reports: “The Limits to Growth” introduced the idea of sustainable economic growth [4
]; “Our Common Future” demonstrated it was possible to reconcile economic growth, environmental preservation and social development [5
]; and the New Urbanism Movement advocated ways to limit dispersed urban expansion of cities by using more environmentally friendly urban design practices such as walkable neighbourhoods, mixed land use and Transit Oriented Developments (TODs) [1
] (pp. 243–266).
The theory of sustainability in the 1990s reconciled social equity, economic growth and environmental preservation with city development [6
] (pp. 296–312), and opened the way for the development of other concepts such as sustainable city [7
], green urbanism [1
], liveable city [8
], and compact city [12
] among others, that are still current and are at the centre of the debate on the influence of urban forms, city designs, use of natural resources, energy and other issues linked to urban sustainability.
The incorporation of climate change issues into the international political agenda in the 2000s brought energy [14
] and resource efficiency [15
] to the centre of the discussion on sustainable development and city sustainability. Discussions on urban forms including energy, resources efficiency and environmental performance became central elements in the search for new concepts and methods to define and measure city sustainability. These latest developments led to the development of the term “green”.
“Green” means different things to different people. The term is nowadays widely used by private and public organisations as a brand for sustainability and eco-friendliness. “Greening” is another term associated to the term green. In this article “green” and “greening” are used synonymously for sustainability and related issues where energy and resource efficiency are central elements.
As a result of the increased attention given to energy, resource efficiency and urban form in relation to climate change, questions already formulated before such as “Are certain urban forms and city designs more sustainable than others in terms of pollution, environmental impact and energy use?”; “What strategies and actions can effectively contribute to make cities more sustainable (greener)?”; and, more recently, “How can we manage the current urban expansion process under the effects of climate change, and at the same time make this process greener?” have regained importance. Although actively being studied up to now there is no critical consensus about the best answers to these questions. Scholars [12
] cited the compact city form as one that could strongly contribute to city sustainability, especially in relation to the impacts of the urban expansion process and the use of energy, resources efficiency, infrastructure and environmental performance related issues. The benefits resulting from the application of this concept cited in the literature can be summarized as: shorter intra-urban travel distances, reduced automobile dependency, increased walking, cycling and use of public transportation, reduced per capita cost of infrastructure provision, influence on the ways cities generate and consume energy, and encouraging the increase of urban density and recycling of already urbanised land.
The Green City Concept is one of the latest responses to the diverse efforts and research conducted to address the problems caused by the dispersed model of city development and to help cities to become more sustainable (greener), less dispersed and more liveable.
Many studies have attempted to define sustainable and green cities [8
] and some have tried to develop concepts and translate these into methods and tools such as benchmarks to measure environmental and/or sustainability performance [23
]. Others have proposed reference guides and frameworks to help prioritize problems and propose city level actions to improve sustainability and environmental performance by using and analysing indicators and policy instruments [28
In general, the various definitions and some of the concepts proposed for green cities address issues related to the three pillars of sustainability theory and a variety of other issues such as health, greenery, resilience and equity. Environment related issues are by far the most often presented in green city definitions, concepts and methods [23
]. The EBRD [26
], for example, defines a green city as one that is characterized predominantly by its environmental performance, with the intention of maximising social and economic benefits. This definition is used to prepare a methodology for benchmarking and prioritisation using seventy core indicators and several elective indicators chosen according to a Green City Pressure–State–Response (PSR) framework. The Economist Intelligence Unit [20
] does not propose a definition of a green city but has developed a benchmark method to measure environmental performance of cities per continent using a group of thirty qualitative and quantitative indicators focused mostly on infrastructure and environmental issues. Zoeteman et al. [25
], uses 87 indicators to investigate (causes of) differences in sustainability performance between EU cities using the three sustainability domains of economy, ecology and socio-cultural aspects. On the other hand, the ADB Green City Development Toolkit [32
] and Solutions for Liveable Cities [33
] are reference guides for ADB staff, consultants, and city leaders introducing key concepts of green city development and outlining a three-step city assessment framework together with a summary of existing tools and resources for green, liveable and sustainable development.
The existence of a broad range of environmental and other urban related issues within a city has resulted in the development of many green city definitions and approaches as briefly mentioned above which has created difficulties for its acceptability and adoption. While some focus only on the environmental aspects, others include socio-economic, environmental and infrastructure elements and others include policies, resilience, ICT technologies and plans such as disaster risk plans, etc. The indexes proposed to measure environmental and/or sustainability performance in general use a large number of indicators which makes them difficult for decisions makers to use and some mix qualitative with quantitative indicators. Many indicators proposed in some of these methods are not regularly tracked by many cities, especially those of developing countries. This lack of uniformity of concepts and approaches to green cities has resulted in a great heterogeneity of methods and indicators for the measurement of environmental and sustainability performance.
The above brief overview of the literature has shown that very different approaches and methods have being developed in relation to green city issues resulting in difficulty in forging a consensus on how and which methods and measures cities should be applied to become greener. In addition, there are still many gaps found in this research that need to be studied, such as the lack of a definition of green city rooted in a simple green city conceptual framework, the development of index methods containing a short number of indicators to measure environmental performance rooted in a conceptual framework, and simple methods to track the evolution and progress of cities’ environmental performance over time. The review of the literature also showed that there is a need for more in-depth research on how population size and GDP influence environmental performance, especially of cities of developing countries with large populations [26
]. No study proposing a method to measure green city performance was found in this review.
Scope of the Paper, Methodological Issues and Objectives
In 2013, due to the growing interest in the subject of green cities, the Infrastructure Group (Today called the Green City and Infrastructure Group.) at the Institute for Housing and Urban Studies (IHS (EUR)) conducted an in-depth literature review on green city issues to gather more knowledge on this field and explore future academic and practical applications. The result of this work led us to use our own knowledge and expertise on urban management, environment, infrastructure, climate change, housing and energy to develop an initial simple green city concept and a tool to be incorporated in our academic activities and to complement our advisory work on supporting cities to become greener. The green city concept was developed by incorporating key findings of the literature, such as elements of the three pillars of the theory of sustainability, and of other concepts including issues such as energy, infrastructure, land planning, greenery and compactness mentioned in the literature review above.
The green city concept is a simple umbrella framework attempting to facilitate the understanding of what a green city is. The conceptual framework called IHS-GCCF is composed of four entry points, seven thematic areas and several promoters. Energy efficiency is the main entry point and also a distinctive characteristic of this concept related to the existing green city concepts. It is assumed in this concept that the overall promotion of energy efficiency in all cities’ activities will help to steward the improvement of city resource efficiency which will ultimately contribute to improving the city’s environmental performance, sustainability and liveability. Within the IHS Green City and Infrastructure Group, it is claimed that a green city, as defined in this framework, is also sustainable and liveable.
The tool called the IHS Green City Index (IHS-GCI) is rooted in the IHS-GCCF and was developed by adapting to our needs the approach proposed in [23
]. It allows us to measure and compare the EP of cities on the same continent over time and contains a small number of quantitative indicators representing key elements of the thematic areas of a developed green city concept.
After being implemented and applied as academic exercises to more than 20 cities from five continents in our Master’s and the Green City for Eco-efficiency Executive Courses, we decided, at the end of 2016, to conduct another literature review on the green city to incorporate some valuable comments received from the evaluations of our programmes, some new developments in the fields of green cities, energy, liveability and sustainability. This would allow us to re-develop the IHS-Green City Index (IHS-GCI) and use the experience gained with the application of the IHS-GCI tool to create a new tool called IHS Global Green City Performance Index (IHS-GGCPI) which is able to measure green city performance over time globally. In this article, the IHS Global Green City Performance Index (IHS-GGCPI) is sometimes referred to as index method, index or just method and fills an important gap in the literature which is the absence of a tool to measure green city performance.
In this article, green city performance (GCP) is also called green performance (GP) and is defined as the sum of the environmental and the socio-economic performances. This definition follows the approach used to build our green city concept framework which incorporated key elements of the pillars of the theory of sustainability and is supported by the fact that some authors [22
] also include the sustainability domains in their own definitions of green cities.
The (IHS-GGCPI) index is rooted in the IHS-GCCF and was developed by adapting to our needs the approach proposed in [20
] and the proposed definition of GP. The index allows us to measure green performance over time but this article only provides a description of how the method can be used to measure GP over time. The GPs shown in this article as a result of the application of the index refer to data collected in the period 2013–2016, a single snapshot which can be used as a base line to calculate the GP for future periods.
The objectives of this article were formulated taking into account some of the literature gaps previously mentioned in this article and are divided into three parts: introduction of the re-developed IHS Green City Conceptual Framework and the IHS Global Green City Performance Index method (IHS-GGCPI; application of the new index method to measure the Green City Performance (GCP) of fifty cities globally and to study the influence of the population size, GDP, energy and key urban sectors in these GCPs; to verify the claim that a green city as defined in our green city conceptual framework is also a sustainable and liveable city.
2. Materials and Methods
The research adopted a deductive approach, building on the state of the art literature on green city and the authors’ knowledge and experience with the environment, infrastructure, sustainability and green city. One key finding in the literature leading to the development of the IHS-GCCF was the presence of some elements of the three pillars of the theory of sustainability in several green city definitions [1
]. In addition, it was found that concepts such as compact cities, greenery, energy efficiency, renewable energy, greenery and green growth [8
] have grown in importance in recent years. The inclusion of elements of the three pillars of sustainability and other issues mentioned above formed the basis for the development of the IHS-GCF and of the IHS-GGCPI. The approach used by the Economist Intelligence Unit [23
] to calculate the environmental performance of cities was adapted to our needs to develop the IHS-GGCPI.
A desk study strategy was used for the revision of the green city concept, the redevelopment of the index and to answer the other objectives of the paper.
2.1. Development of the IHS-GGCPI Method: Steps and Procedures
The re-develop the IHS-Green City Conceptual Framework (IHS GCCF) displayed in Figure 1
the IHS-GGCPI method index was enhanced by using the key findings in the literature on green cities as well as using the authors’ own experience with green issues.
The steps and the procedures adopted to develop the IHS-GGCPI method are described below. They are slight adaptation of the procedures used to create the previous IHS-GCI:
Step 1: Selection of indicator for the IHS-GCGPI and assigning weights to the indicators
The re-developed IHS green city conceptual framework (Figure 1
, Item 3.1 (results)) was used as the base to choose the indicators to compose the new method. These indicators were selected taking into account key aspects of the green conceptual framework and the following criteria: the indicators should represent elements of the green city concept shown in Figure 1
. The index should contain a maximum of 30 quantitative indicators representing aspects of the three pillars of sustainability (social, economic and environment) and linked to the elements of the newly re-developed IHS-GCCF. The selected indicators needed to be regularly monitored in cities globally and the data to be collected for these indicators should be published in any official local, national or international institution during the period 2013–2016.
2.1.1. Initial Selection of the Indicators and Pilot Test
Using the above criteria, an initial set of 32 indicators were selected and pilot tested on ten cities (two per continent). These indicators were tested to assess the availability of data, if they were regularly tracked and if the definition used matched the definition we have adopted. The criteria used to select the ten cities for the pilot test were: cities with high economic importance and high income for the country, well recognised high environmental quality, with a large and medium population and finally cities that regularly use indicators to monitor and make available data on its socio-economic and environmental situation.
The pilot test was conducted in two rounds of five cities: Johannesburg, Shanghai, Buenos Aires, Berlin and Mexico City; and Lagos, Delhi, New York, Sao Paulo and London. After each round, an assessment of the initial proposed list of indicators was conducted in relation to the defined criteria.
As a result of the first round, some indicators were dropped and definitions were adapted. The dropped indicators included the ones proposed to measure governance, the level of education, urban agriculture, water quality, energy intensity and CO2 equivalent per capita for electricity consumption. The first four indicators were dropped because it was hard to find one single indicator representing these areas and a uniform description for the indicator. The other two were dropped because of the lack of regular data measurements and inconsistent definitions. The ICT indicator definition was changed from the number of mobile telephones in a city to internet penetration regardless of the access method, and mass transport was redefined to include only heavy rail metro, subway systems and commuter rail systems for whose lengths records usually exist.
The assessment conducted in the ten cities included in the first and in the second rounds showed that for three indicators, share of wastewater treated, share of solid wastes collected and population living in slums some rich cities have ceased to regularly track them. These cities however usually have laws requiring them to comply with high standards in issues related to these indicators. Once these indicators represent important aspects of our green city concept and are also important to measure green city performance of cities of developed and developing countries, the following assumptions were made for the rich cites that have ceased to regularly track them: share of wastewater treated higher than 97%, solid waste collected higher than 95% and populations living in slums less than 0.3%. These numbers are within the range of the top score (5) of the IHS-GGCPI and means that cities with data for these indicators, within these ranges, are among the top twenty percent cities with the highest GPs. Another reason to propose these numbers is the fact that in practice cities do not treat or collect 100% of their wastewater or solid waste and some residual precarious residences still exist in these cities. An explanation of the construction of the scoring system and the ranges is presented in Step 2.
2.1.2. Final Retained List of Indicators and Assigned Weights (Wav)
After the assessment of the pilot test, twenty-five indicators distributed across eight sectors and divided into two groups were selected. Table 1
presents the final list of indicators per group and sectors with respective units and definitions. The administrative area, although included in the list of the indicators, was not used to calculate the city green performance. Its role was to define the geographical (surface) area of the cities where the data were collected.
2.1.3. Assigning Weights to the Selected Indicators (Wav)
After selecting the final list of the indicators, a weight was assigned to each indicator. The procedure adopted was: distribution of the final list of the indicators divided into eight sectors (Table 1
) to ten IHS academic staff (including the two authors) familiar with the objectives and with the IHS-Green City Conceptual Framework. Each staff member was asked to weigh the indicators to a maximum of 100% for each sector according to their importance to the IHS-GCCF. After the weights were assigned the average weight (Wav) was calculated and later used to calculate the green performance of each indicator. The weights represent the importance that different stakeholders and experts give to the indicators of the tool in line with our conceptual framework; therefore, we decided to involve a group of experts in the process of assigning weights to incorporate a greater diversity of importance, and not to restrict the importance attributed by the two authors. The weights shown in Table 1
are the average of the weights given by the ten experts including the two authors.
Step 2: IHS-scoring system
The scoring system for the global index was created using the total new data collected for the twenty-five indicators of the fifty studied cities. The total collected data were normalised using a range of 1–5. The scores were classified as 1 point (signifying well below average), 2 points (below average), 3 points (average), 4 points (above average) and 5 points (well above average). This normalisation procedure was made to allow the different data values to be comparable and to construct aggregate scores for each city. The score in the index represents the rank of the fifty cities examined on a quintile based comparison. A city that has a score of 1 is in the bottom 20% of all cities, a score of 2 implies the city is between the bottom 20% and 40% of all cities and so on. A city with a score of five, means that it is better than 80% of cities.
Step 3: Calculating and explaining Green City Performance over time
To better understand the procedures involved in calculating the GCP of the indicators, sectors and cities and explain any change (increase, reduction or no change) in GCPs calculated in the studied period, we have prepared an excel spreadsheet (matrix) as shown in Table 2
that guides the users in this process.
2.1.4. Explanation on how to use Table 2 to calculate Green City Performance
In the column with title Sector, and column with title Indicator, the user(s) will find the names of the sectors and the indicators per sector with their respective definition.
In the column with title Average weight (Wav), the user(s) will find the average value assigned by the IHS staff to each indicator (see description of assigning weights in the Step 2 above). In the previous IHS-GCI, the users (students) needed to assign weights following a given set of instructions and later calculate the average weight of each indicator to be used in the next steps.
In the column with title V1 and named Old value, the user(s) will copy and put in this column the values of the data for each indicator collected by IHS in the period 2013 to 2016. In the next column titled Year, it should be indicated the year and the source of the data.
In the column with title V2 and named Updated value, the user(s) need to search for each of the twenty-five indicators new updated data using internet and other sources and fill in this column. In the next column titled Year it should be indicated the year and source of each updated data.
Using the IHS score system of Table 2
, the user(s) needs to score the data of the indicator V1 and put the result in column titled S1. Repeat the same procedure for the V2 and put the result in column titled S2. The scoring procedure refers to score the value of the old and updated data to one value of the range 1–5 where 1 represents Well below average (1 point) and 5 Well above average (5 points); see Step 2 of the method.
The next procedures refer to the calculation of the old and updated GCPs. The GCP of the indicators is called weighted score (weight times the score). These values are put in the column titles: Weighted old score (S1wav) and Weighted new score (S2wav). The GCP of a sector is calculated by adding the weighted score for all indicators of the sector: columns titles Σ old GCPs of indicators of the sector and Σ new GCPs of indicators of the sector. Finally, the total GCP of the city for the two studied periods are calculated as the Σ old GCPs of all sectors for the period 1 and the Σ new GCPs of all sectors for period 2.
Explaining any changes in GCP over time in columns titled Qualitative indicators and Explanation. In the first column, the user(s) need for the studied period and per sector search on the Internet and in other sources for qualitative indicators, such as policies, plans, programmes, projects, awareness campaigns, etc., related to any indicator(s) of the sector and implemented by the studied city during the studied period. In the column titled Explanation, the user(s) should provide a short discussion using the identified qualitative indicators and if necessary other relevant information, such as for example factors related to socio, economic, migration, political changes, governance, etc., to try to explain any changes (increase, reduction or no change) in the calculated GCP over time.
2.2. Assessing the Claim that a Green City Is also a Sustainable and Liveable City: Procedures
Two different procedures were developed to assess the above claim: one to measure the claim that a green city is also a sustainable city and the other that a green city is also a liveable city.
Two approaches were developed to investigate if a green city as defined in our GCCF is also a sustainable city: the first approach consisted in conducting an in-depth literature review of the concepts of sustainability, compact city, sustainable city, liveable city and green city to build and revise the green city concept as presented and discussed in the Introduction; and the second approach consisted in calculating correlations between the total green city performance calculated using the GGCPI method with the green performance of the socio-economic group and with the green performance of the environmental group of this method and, finally, calculating the correlation between the green performances of the socio-economic group with the green performance of the environmental group.
The procedures developed to investigate if a green city as defined in our GCCF is also a liveable city used the calculation of correlations between the total green city performance measured using the GGCPI and the total liveability performance calculated using the new developed liveable performance index described below:
The approaches used to develop the IHS-Liveability performance index followed more less the same approaches and the steps used to build up the IHS-GGCPI. These approaches and steps are described below.
2.2.1. Selection of Liveability Indicators
Several articles have shown that the liveability concept is linked to the concept of sustainability [8
]. Other authors [10
] emphasized that, although the liveability concept contains diverse elements of the concept of sustainability, it is particularly focused on special characteristics of the place where people currently live, such as the quality of life, health, safety, accessibility and well-being of the local communities.
From the mentioned papers, we selected twenty indicators used or mentioned by the above cited authors to measure liveability, and compared these selected indicators with the indicators of the IHS-GGCPI in Table 1
. Fourteen indicators of the liveability list matched the indicators of the GGCPI. These indicators were selected to form the liveability performance index, as shown in Table 3
2.2.2. Assigning Weights for the Liveability Indicators
The fourteen indicators selected to form the liveability index were distributed to five IHS staff familiar with the liveable city concept and asked to assign weights to these indicators to a maximum of 100%. The average weights were calculated as shown in Table 3
and used to calculate later the liveability performance.
2.2.3. Calculating the Liveability Performance
The same score systems developed for the IHS-GGCPI method were used to score the indicators selected to measure liveability. This approach is justified because the liveability indicators are also indicators of the IHS-GGCPI.
The liveability performance of each indicator is the weighted score of each indicator. The weight used in this calculation is the average weight assigned to each liveability indicator shown in Table 3
. The total liveability performance of a city is the sum of the liveability performances of the fourteen indicators.
2.3. Data Analysis
The data collected for the fifty cities were processed using Microsoft Excel statistical analysis tool. A Pearson correlation was used to identify possible influence of key indicators and sectors on the green city performances. The confidence interval was kept at 95% with a level of confidence of 0.05.
The ranking of Green City Performance was prepared by calculating the GCPs of the fifty cities using the new developed index method (IHS-GCCPI). These results were arranged in a descendent order (top to down) green performance.
To help the analysis of the calculated green performances, three clusters of GCPs were formed: high, middle and low GCP. The approach used to form these clusters consisted of dividing the fifty cities into groups with approximately the same number of cities. The results of these clusters were further analysed in relation to the green performances of the sectors and key indicators such as sanitation, population size, GDP per capita, energy, air quality and others.