Urban sustainability indicators: Challenges and opportunities

Ecological Indicators 93 (2018) 282–291

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Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind

Review

Urban sustainability indicators: Challenges and opportunities Pramit Verma, A.S. Raghubanshi

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T

Integrative Ecology Laboratory (IEL), Institute of Environment and Sustainable Development (IESD), Banaras Hindu University, Varanasi 221005, India

A R T I C LE I N FO

A B S T R A C T

Keywords: Indicator application Indicator evaluation Indicator framework Sustainability targets Urban sustainability

Urbanization has become one of the most important issues which define the human relationship with the ecosystem. Measuring progress towards sustainable or unsustainable urban development requires quantification with the help of suitable sustainability indicators. There is a general ignorance about contextual meaning and understanding of the concept of sustainability which differs from country to country and economic strata of the society. Our review aims to reduce this challenge by identifying major issues faced in the development and implementation of sustainability indicators in an urban context and suggesting remedial recommendations. We have identified two broad categories of challenges according to their development and implementation phase respectively, and three preliminary criteria in the application of urban sustainability indicators.

1. Introduction

This accumulation of anthropogenic assets is the result of growth in economic and social status. Sustainable development has been traditionally identified with three major areas of environmental, economic and social dimensions along with institutional addendum. Sustainable development must be equitable, liveable and viable (Tanguay et al., 2010). It is considered a weakness that sustainability has a loosely defined conceptual base (Pissourios, 2013), with lopsided progress in the multiple dimensions of sustainability, chiefly environmental aspects. It is claimed by many authors that definition of sustainability transforms itself according to the target area of researchers (Tanguay et al., 2010). According to Turcu (2013), there is generally no universally accepted definition of sustainability. Sustainable development means achieving enduring development addressing human needs and improvement of the quality of life. At the same time, natural resources should be utilized at a frequency and degree that can be sustained by regenerative capacity of the ecosystem. Mori and Christodoulou (2012) supported nested hierarchical approach for biophysical, social and economic aspects of sustainability. They argued that in the triple bottom line structure social, economic and environmental considerations cannot be treated as parallel. Functioning life-support system, social structures, institutions, and economies depend on each other to keep working. Though they have explained this approach with a limited scope, it is important to mention that nested hierarchy approach considers biophysical limits of the earth as the final boundary which contains and consists of social and economic parameters (Fischer et al., 2007). Sustainable development definition gives rise to multiple interpretations (Tanguay et al., 2010), with differing emphasis on “what is

The ecological footprint of cities extends much beyond their administrative boundaries, with the productive and assimilative services of ecosystem facilitating the flow of energy as well as material. The resource base used by urban population is generally found away from its place of consumption. Therefore, biophysical consequences of rapid and uncontrolled urbanization are felt elsewhere. Urbanization is a large proportion of the human population living in cities (Davis, 1955). According to United Nations it is movement of people from rural to urban areas accompanied by three major trends (Mori and Christodoulou, 2012): first, concentration of ‘metacities’, that is, conurbations of more than 20 million people, in the developing countries of Asia, Latin America and Africa (Habitat, 2006); second, presence of more than half of world’s urban population in cities of less than 500,000 inhabitants; and third, 95% of urban population growth in cities of developing countries accounting for about 4 billion people (Habitat, 2006; Mori and Christodoulou, 2012). India and China, in particular, are expected to see an increase of about one-third urban population in the coming decade with rapid urbanization (Shen et al., 2011). Following the aforementioned three trends, urban growth is dynamically balanced between economies of scale and scope, along with diseconomies like environmental degradation and leakages (Munda, 2006). Cities are confronted with the problem of trade-off between positive and negative effects of urbanization with respect to environmental, social and economic aspects (Mori and Christodoulou, 2012). As cities grow anthropogenic assets accumulate while natural assets suffer a corresponding decrease (Bithas and Christofakis, 2006).

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Corresponding author. E-mail address: [email protected] (A.S. Raghubanshi).

https://doi.org/10.1016/j.ecolind.2018.05.007 Received 8 October 2017; Received in revised form 19 February 2018; Accepted 3 May 2018 1470-160X/ © 2018 Elsevier Ltd. All rights reserved.

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Table 1 Definition of sustainability: Economic, Social and Environmental. Theme

Urban Sustainability

References

Economic

It should focus on man-made, natural, human and social capital Resource utilisation should not affect future income Intergenerational equity for resources Economic activity should consider ecological basis Intergenerational equity, distributional equity, optimal growth

Hamilton (2006) Moldan et al. (2012)

Should address the perpetuity of social values, identities, relationships and institutions Common goals and social cohesion Health, education, food, water, housing should be sustained for each individual

Black, 2004; Moldan et al. (2012) Gilbert et al. (1996) Gilbert et al. (1996; Longoni and Cagliano (2015); Moldan et al. (2012) Longoni and Cagliano (2015)

Social

Anand and Sen (2000)

Actively support the maintenance and creation of skills as well as the capabilities of future generations Environmental

Social and economic development should have sound environmental foundation Natural resource management should have high priority Tipping points, thresholds (air, water pollution levels), sudden changes should be well understood

Moldan et al. (2012) Moldan et al. (2012); Booth et al. (2016)

by concrete indicators and some goals also have a “means of implementation” which includes finance, trade, technology transfer, etc (Le Blanck, 2015). For example, Goal 17 presents a cross-cutting theme of targets which includes finance, trade, multi-national cooperation, and capacity building to facilitate implementation of the other 16 SDGs. These indicators and targets are theoretically aimed to be universal but practically they are not applicable to every country (Hák et al., 2016). Goal 11 of SDG, making cities inclusive, safe resilient and sustainable, addresses urban sustainability and includes the following cross-cutting issues of affordable housing, sustainable transport, human settlement planning and management, green and public spaces, supporting positive economic, social and environmental links between urban, periurban and rural areas and developing and implementing, in line with the Sendai Framework for Disaster Risk Reduction 2015–2030, a “holistic disaster risk management at all levels” (United Nations, 2018). Indicators proposed to measures these targets include, but are not limited to, proportion of population living in slums, ratio of land consumption rate to population growth rate, total and per capita expenditure on preservation of natural and cultural heritage, solid waste collected, proportion of local governments that adopt disaster risk reduction strategies according to the Sendai Framework for Disaster Risk Reduction 2015–2030, etc. (Inter-Agency and Expert Group in Sustainable Development Goal Indicators, 2016). SDG targets have emerged from a long process of political negotiations. Sustainable Development Services Network (2015) states that when these targets were assessed for their scientific robustness it was found that only 49 targets out of 169 had a well-developed scientific background. 54% of the targets needed to be more specific in terms of their scope while 17% needed significant improvement (Sustainable Development Services Network, 2015). Lack of implementation, conflict between targets and goals, and between international agreements and political foci, unavailability of data and non-quantifiable targets were the major weaknesses found in the assessment (Hák et al., 2016). From Table 1 it is clear that all aspects of sustainability arise from human activities, like resource use, pollution, need to understand a system’s capacity, intergenerational equity and tipping points among many others. Since these activities are concentrated in urban areas (Mehta et al., 2016), urban sustainability works as a cross-cutting issue across the environmental, social and economic sustainability. Here space is used to define sustainability (Wang et al., 2016). The inflow of materials and energy resources and generation of wastes should not exceed the city’s capacity for a sustainable environment (Science for Environment Policy, 2015). Economic activity, population growth, infrastructure and services, pollution and waste should be internally limited in the system so that urban system may develop in harmony, internally limiting negative impacts on the natural environment (Hiremath et al., 2013). At this point, mention should be made about

to be developed, what is to be sustained”, the relationship between environment and development and the temporal scale of such development. This means that in order to be sustainable, those resources which can be utilized for development should be identified with their limitations (carrying capacity), along with the natural components or limits that need to be protected or sustained respectively for the proper functioning of ecosystems. Sustainability is a very “loosely” defined term (Pissourios, 2013; Turcu, 2013). The broader concept ideally includes the triple bottom line, however, the concepts get more focused to include mostly environmental sustainability in practice. Sustainability is the most “challenging and controversial” issue with regard to its “interpretation and application” and further when the term ‘sustainable’ combines with ‘development’, its focus changes to economic development rather than overall sustainability (Lee and Huang, 2007). When nations focus on economic development as the main aspect of sustainable development it inevitably drains the earth’s regenerative and carrying capacity. Social influence on the concept of sustainability renders its measurement less objective, limited to a certain scope, with a possible conflict of interests and manipulation by stakeholders. Further, according to Moldan et al. (2012) social sustainability is the most important pillar of sustainable development and yet it is not fully clear as to what it consists of. They question whether it includes growing, or not diminishing, inequality between people or nations, good health or failure of national institutions. Mori and Christodoulou (2012) have identified the triple bottom line as an abstract notion of biophysical, economic and social elements, and intergenerational equity as the fundamental notions of sustainability and Turcu (2013) holds that definition of sustainability is a normative choice rather than a concrete well-defined concept. According to Pupphachai and Zuidema (2017), sustainable development provides a more general direction for evaluating and streamlining policies towards urban function and structure rather than a precise definition. This very fact has resulted in the development of Sustainable Development Goals with 17 broad goals and 169 interconnected targets based on national priorities (United Nations, 2015). Mori and Christodoulou (2012) argued that cities have social and economic impacts on sustainability while they export their environmental externalities to areas out of their boundaries. This notion is very important in assessing the sustainability of urban areas as they extend much beyond their administrative boundary. Sustainable Development Goals (SDGs) and targets were adopted in 2015 (Kumar et al., 2017b) for the next 15 years with the specific aim of achieving a holistic approach towards sustainable development for both developing as well as developed countries (Griggs et al., 2013). These goals are believed to be more integrated into policy than Millennium Development Goals (MDGs) as nations can prioritize the targets and goals over national scales and local conditions (Le Blanck, 2015) while working with internationally accepted norms. SDGs are accompanied 283

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of urban machinery. Dizdaroglu (2015) states that indicator-based sustainability assessment contributes in the following four ways, first, by indicating the state of local sustainability, second, quantifying sustainability, third, by providing feedback of policies during implementation, and fourth, by finding the best policy measures for sustainability.

lack of urban boundary concept. Politically urban boundaries are defined as countries, states, cities and various other terms. They have an advantage in terms of implementing policies and evaluating progress. Measuring sustainability based on these boundaries is easy to understand for decision-makers and stakeholders. Since urban areas extend beyond their political or administrative boundaries, sustainability measured for politically defined urban areas is irrelevant, arbitrary and diminishes the ground reality (Fiala, 2008). However, importance of political and administrative boundaries persist, and cannot be challenged, because they provide an existing pathway for delivering sustainable policies to the society. For more information about models of sustainability see Ali-Toudert and Ji (2017). The Brundtland Commission defined sustainable development in its landmark report ‘Our Common Future’ (WCED, 1987). According to it sustainable development means utilising resources in order to meet the present needs of society as well as making efforts to use the resources in an optimum manner within their regeneration capacity. Moldan et al. (2012) gave three important aspects for defining sustainable development, first, development is to first satisfy “certain basic human needs” before higher needs can be fulfilled, second, such development should be in harmony with nature, and third, sustainable development is a human-centric concept with intergenerational equity at its heart. While the Brundtland definition of sustainability leaves ample room for interpretation and growth, it is considered that human beings are the focal point in any discussion about sustainable development, and they are entitled (Moldan et al., 2012) and responsible to create a “healthy and productive life in harmony with nature.”

2.1. Urban sustainability indicators Newman and Jennings (2012) defined sustainable urban ecosystems as “ecosystems which are ethical, effective (healthy and equitable), zero-waste generating, self-regulating, resilient, self-renewing, flexible, psychologically-fulfilling and cooperative” (Dizdaroglu, 2015). Sustainable urban development includes (1) improving quality of life through social interaction and easier access to wide range of services; (2) minimizing energy consumption via green building design technologies; (3) sustainable transport; (4) environmental protection and restoration (Dizdaroglu, 2015; Dizdaroglu & Didem, 2017; Jabareen, 2006); (5) renewable energy and waste management (Stossel et al. 2015); (6) green economies including clean technologies, green tax policies, green infrastructure, etc. (Zygiaris, 2013); (7) environmental justice and equity through public health and welfare by natural resource management including affordable housing, efficient transport, community participation into policy decisions, etc. (Wolch et al., 2014); (8) Preservation of public space, cultural and natural heritage (Fawzi Raed Ameen and Mourshed, 2016) and water resources including groundwater (Kumar et al., 2017a). Urban sustainability includes a number of topics like biodiversity, energy, material balance, air pollution, heat island, noise pollution, etc. Sustainable urban indicators are defined by Peter et al. (1998) as “physical, chemical, ecological or socio-economic measures” which can measure environmental or complex ecosystem variables (Dizdaroglu, 2015). While indicators help in measuring progress towards sustainability, their application is not easy across different cities or regions. Cities have different definitions of sustainability, indicators designed to measure sustainability for a particular city cannot be used for a different city (Li Shen & Guo, 2014). Apart from a spatially focused approach there is no special criteria for urban sustainability indicators that sets them apart from sustainable development indicators.

2. Sustainability indicators Measuring progress towards sustainable or unsustainable development requires quantifying phenomena which represent such progress. This is done through indicators (Cutaia, 2016). Indicators could be anything from as simple as Gross Domestic Product (GDP) per capita to measure economic development to complex such as immunization against infectious childhood diseases to measure health care. First set of indicators were published in 1996 by the UN Department of Economics and Social Affairs in the form of Driving force – State – Response (DSR) framework (King, 2016). Indicators are required at all levels of resultsoriented development goals. These indicators provide the necessary information for measuring environmental, economic and social progress (Böhringer and Jochem, 2007). Indicators help towards achieving sustainability targets and inform policymakers as well as the public about the current state of the environment, their weaknesses and strengths, and bring out the priority areas (Pupphachai and Zuidema, 2017). Indicators not only validate a framework but also provide an insight into the phenomena being monitored (Guzm’n et al., 2017). Simple indicators are those which measure individual phenomena such as number of people living below poverty line and percentage green cover, while they combine to form a composite index based on different weightage given to constituting indicators. Both help in measuring, analysing and implementing sustainable practices, in policy making and public communication (Dizdaroglu, 2015; Singh et al., 2009). Sustainable development indicators must clearly differentiate between sustainable and unsustainable development and results should be clearly stated without any confusion for policy making (Lee and Huang, 2007). Sustainability indicators can be a normative measure indicating the distance between current and baseline states (Huang et al., 1998). They reflect policy measures, and hence, policymakers and those affected by such policies are the best judge to predict the feasibility of implementing such measures. Hence, indicators which receive political support are liable to be more successful and accepted (Science for Environment Policy, 2015). Measuring sustainable development in urban areas remains the greatest challenge in implementing sustainable development in cities (Lee and Huang, 2007), which requires comparable information about the social, economic and environmental aspects

2.2. Scope of the review and bibliometric analysis Our aim was to analyse challenges in the application of sustainability indicators in urban areas. In this review article, we have focused on research published in peer-reviewed journals in the last decade from the year 2006. We followed a three-step approach in our literature review similar to Guzm’n et al. (2017) and Srivastava et al. (2017). A key phrase search was performed to finalise the literature considered on the basis of whether they dealt with urban sustainability indicators, followed by the second step, a reference analysis related to indicator application and development, and the third step, identifying challenges and recommendations. We found that publications related with urban sustainability indicators frequently had “urban”, “sustainable development”, “sustainability” and “indicators” in title, abstract or keywords. Based on this initial observation we searched for keywords of “urban sustainability indicators” or “sustainable development indicators” in the title, abstract or keywords in the Scopus database on 3rd October 2017, since our focus was on understanding the indicators applied in an urban setup. The scope of the search included 341 documents pertaining to fields of environment, social, energy, engineering, business, management and accounting, economics, agricultural and biological sciences, earth and planetary sciences, decision sciences and multidisciplinary sciences. These broad fields of study were considered in the bibliometric analysis due to the cross-cutting nature urban sustainability. We further refined to those publications which had the word “urban” in their title, abstract or keywords for the next step. We found 284

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the reader with recent developments in this field. 2.3.1. General research content This section gives a brief account about global or regional organizations active in the formulating or utilising urban sustainability indicators followed by general conclusions from some research work done in the last decade. The World Bank categorises three types of indicators, first, a large number of indicators covering various environmental concerns comprise individual indicators; second, a small set of indicators for evaluating environmental policies come under thematic indicators; and third, systemic indicators where one indicator represents a difficult issue (Dizdaroglu, 2015). A Global City Indicators Program was started in 2007 by the World Bank which provides a platform for cities to compare their indicators and share results and best practices regarding sustainable urbanization (Zoeteman et al., 2016). This program is run by the Global City Indicators Facility (GCIF) at University of Toronto. The World Bank also provides an assessment tool, called TRACE, which uses 28 main performance indicators to measure the energy consumption of cities (Zoeteman et al., 2016). World Resources Institute identified four categories of indicators. The first category, called source indicators, is based on depletion of resources and degradation of ecological systems, like forest, marine, and freshwater; second, sink indicators measure the capacity of resources to sustain emissions and waste; third, life support indicators assess change in Earth’s ecosystems and biodiversity; fourth, human impact indicators evaluate the effect of environmental degradation on human health and well-being (Dizdaroglu, 2015). These indicators were specifically designed to capture the anthropogenic and environmental interaction. It is worthy to note that indicator-based literature and independent studies are extensively available for European and North American countries at the national level while they are hard to find for Asian and African countries. Zoeteman et al. (2016) have given an account of indicator studies limited to European cities. EUROSTAT developed a monitoring framework called Urban Audit for European Union countries with the help of national statistics organizations. It began in 1999 as a socioeconomic measuring tool collecting data at regular intervals and publishing the results in EUROSTATS’s Regional Yearbooks. Urban Audit data informs about the sustainability of urban regions of the European Union (Zoeteman et al., 2016). Other indicator studies include the World Health Organization (WHO) European Healthy Cities Network collecting data since 1998 which published a city fact sheet for 100 European cities for twelve health indicators; the European Green City Index for thirty European cities evaluated thirty environmental indicators; the Covenant of Mayors on Climate Change, 2014, provides greenhouse gas emissions and reduction targets set by participating cities (Zoeteman et al., 2016). Lee and Huang (2007) proposed a set of 51 indicators for Taipei sustainability to assess which public policies lead towards sustainable development. They calculated composite indicator values for four themes of economic, social, environmental and institutional categories. Their indicator set belongs to weak sustainability framework and they have highlighted the method through which balance can be reached between anthropogenic and ecological aspects of indicators. Urban areas are characterised by a concentration of built areas. (Xing et al, 2009) identified an urban sustainability model based on monetisation of the buildings in an urban area. The aim was to determine sustainability by analysing and internalising the cost of environmental, social and economic externalities. Their study was focussed on the building and urban planning cycle. On the other hand, a study with a new perspective by Sakieh & Salmanmahiny (2016) compared the urban growth to cancer spread in human bodies. They argued that urban cores behaved like cancer cells that constitute a neoplasm or a tumour. They have given arguments comparing the spread of cancer cells with urban cores stating that like cancer cells, priority needs to be to restrain the larger urban cores with more physical and population size as they have bigger and extended ecological footprint. While the smaller cancer

Fig. 1. Composition of peer reviewed literature in 2006–2017 indexed in Scopus database according to article type.

Fig. 2. Timeline of number of articles selected for our review published in the field of urban sustainability indicators 2006–2017 indexed in Scopus database.

108 research articles, 14 conference proceedings, 10 review articles, 2 articles in press and 1 book out of a total of 138 research publications (Fig. 1). Research publications have peaked in the year 2012 with 22 publications, while they were only 3 and 13 in 2006 and 2015 respectively. Research in this field has increased in the last decade (Fig. 2) warranting a streamlining of its direction. Second, we did a reference cross-check and found some of the older reports and other works from different agencies showing important developments which we included for a proper explanation of concepts. Third, analysis of literature was done to find out the specific issues related to development and application of urban sustainability indicators. Only those papers were selected for review which were closely related to the urban sustainability indicators and not focussed on a particular urban sustainability theme. Duplication of ideas was avoided to include maximum aspects of recent studies and trends in urban sustainability indicator research.

2.3. State of research There are several organizations involved in developing and applying indicator-based sustainability frameworks. From a review of current state of research, the following account about urban sustainability indicator research and methodologies being employed in such research has been given. This section is divided into general research content and recent trends in research methodologies. The focus is to familiarize 285

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three areas of airborne particulate matter concentration, biomass burning and coastal chlorophyll trends. For airborne particulate matter concentration, they created an exposure index from human health policy perspective using population weighting. For example, population weighting gave more weight to PM2.5 concentration in more populated areas. They used Moderate-Resolution Imaging Spectroradiometer/ Multiangle Imaging Spectro-Radiometer (MODIS/MISR) data for aerosol optical depth measurements and Global Rural-Urban Mapping Project for applying population weighting to spatial grids. Their main methodological achievement was that they used satellite imagery to create sustainability indicators thereby proving the relevance of using satellite data in urban sustainability measurement. Salvati and Carlucci (2014) applied a Factor Weighting Model to create an index of sustainability. The methodology followed to select indicators included seven steps for variable selection, data transformation, multivariate analysis, weight derivation, indicators composition and descriptive statistical analysis of the derived index. They also conducted a PCA to find out the factors affecting socioeconomic and environmental conditions for 8100 municipalities of Italy. They further compared their derived index with target indicator values for Italy. Cook et al. (2017) developed a simple index applying two different but complementary approaches. They used a proximity-to-target approach in case of quantifiable targets and, where trend-based targets were present, a traffic lights approach was applied. Basically, they quantified progress towards or away from accepted targets of sustainability. Since there is no limit for trend-based indicators, a reference point was found out wherever data was available and a traffic lights approach used, where red meant deteriorating, green meant improving, yellow meant little or no change and grey meant data not available. A set of 23 indicators were selected from 30 indicators against five key criteria of policy relevance, utility, soundness, interpretability and data availability and quality. In a recent study Luan et al. (2017) gave a comprehensive index based on sensitivity analysis of 18 indicators taken from an existing index. They applied the extended Fourier amplitude sensitivity test (EFAST) model to quantitatively determine the importance of sustainable development indicators. Their study brings out the fact that there is a need to simplify the sustainable development evaluation process because of over-population of such indicators.

tumours have more potential for growth they can be mitigated more easily than their larger counterparts. Same holds for the urban cores. They analysed the suitability of different landscapes for urban growth, rangeland development and afforestation under three scenarios of restricted urban growth with more potential for afforestation, rangeland protection scenario with more potential for urban growth and a historical growth scenario where the whole of the study area was available for urban growth. Shen et al. (2011) proposed an International Urban Sustainability Indicators List (IUSIL) after examining nine different practices followed in some cities. They concluded that sharing knowledge about different practices leads to the selection of indicators and communication of comparative results. Their main drawback was that they did not examine these practices against their implementation in these cities. Panda et al. (2016) developed a composite Urban Social Sustainability Index (USSI) under four themes of sustainability viz. economic, social, environmental and institutional. Turcu, (2013) emphasised the importance of incorporating local perspective by integrating science and public as policy tools. Such indicators may reflect a more ‘truthful image of local (un)sustainability’. But the methodology by Turcu, (2013) would be hard to reproduce by local governments or public. Babu and Datta (2015) reported that there exists a bidirectional association between developmental and environmental aspects in the developing countries that are more dependent upon natural resources. They have shown that a 1% growth in life expectancy contributed to $10291.46 increase in GDP, whereas 1% rise in GDP resulted in marginal growth in life-expectancy and same was the case for GDP and adult literacy rate. This meant that growth in GDP did not immediately translated into health and education improvements. GDP does not consider the diseconomies like deforestation, water quality degradation, soil erosion, biodiversity loss, air pollution, depletion of fisheries stock, etc. They have argued in support of eaNDP (environmentally adjusted net domestic product). 2.3.2. Recent trends in research methodology Methodologies applied in various works have been cited here with a brief explanation to highlight the wide spectrum of urban sustainability indicator development and applied research. We found that multivariate statistics like factor analysis (Huang et al., 2015) and Principal Component Analysis (PCA) (Huang et al., 2015; Mascarenhas et al., 2015) were one of the most useful methodologies (see Supplementary Table S. 2). Recent developments in the application of earth observation data analysis are becoming increasingly advantageous in indicator studies (Salvati and Carlucci, 2014; Huang et al., 2015). Zhang et al. (2010) applied principal component analysis (PCA) to determine the most useful indicator sets. Their basic premise to assess indicators was that urban land use is driven by several factors like social and economic, the aim is to find out the most important components from available indicators. They reported that following indicator variables formed the first three factors of PCA: Factor 1 – Gross Domestic Product (GDP), GDP per unit area of land, investment devoted to environmental pollution treatment, total land area and retail sales of consumer goods per unit area of land; Factor 2 – Proportion of construction land cover in the built-up urban area and road area per capita; Factor 3 – Proportion of industrial solid wastes that are treated and reused and population density. (Sakieh & Salmanmahiny (2016) validated their morphological cancer analogy by using Multi-Criteria Evaluation, SLEUTH land use change model and performance metrics to compare cancer growth and urbanization pattern. Panda et al. (2016) used normalization of data values, weighting through expert survey and confirmation through factor analysis, determining directionality of the scores and linear aggregation of the thematic index in computing USSI. Their use of multivariate statistics to test their model was in resonance with suggestions of Huang et al. (2015) for indicator development and similar to the methodology followed by Salvati and Carlucci (2014). De Sherbinin et al. (2014) developed a set of indicators focussing on

3. Discussion This over-population has created a need to identify the challenges faced in indicator research so as to distil its content based on relevance and applicability. A number of authors have identified challenges faced in developing, selecting and implementing sustainability indicators in general (Hák et al., 2016; Lee and Huang, 2007; Moldan et al., 2012; Mori and Christodoulou, 2012; Tanguay et al., 2010; Turcu, 2013). Since urbanization has become one of the most important issues which defines the human relationship with the ecosystem, we have focussed on the urban context of sustainability indicators. The indicator selection, baseline and target determination, evaluation and review cycle for applying urban sustainability indicators in a top-down framework is described in Fig. 3. 3.1. Challenges and opportunities After extensive review of literature, we identified external and internal challenges as two broad categories through which sustainable development indicators can be analysed. This grouping was aimed at simplifying the most common issues met during development and implementation of indicators. Internal challenges are the problem inherent in indicators due to their development methodology. Their causes can include, but are not limited to, methodology used for developing indicators, weighting methods, complexity or over-simplicity in measurement and lack of theoretical base. External challenges are the issues which prevent implementation of 286

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Fig. 3. Diagram showing the steps involved in top-down approach in an indicator framework along with constituents of each step.

framework. It is determined by government policy, government departments involved, the scope of urban boundary, time period and whether updated urban conditions (Liyin Shen & Zhou, 2014) are taken under consideration. Urban conditions refer to the local, regional and global interactions in an urban setting which give it its unique identity. Urban setting defines the relationship between indicators and urbanization. Stossel et al. (2015) stated that urban sustainability assessments mostly focus on environment within city boundaries. Zhou et al., (2015) cited the importance of public departments in creating indicators as they were the ones that had to implement and report progress about sustainable development. They proposed a responsibility-based method in which roles and scope of all concerned public departments were taken into account. Setting goals (B) is the second step of indicator development. Stakeholder participation is the principal activity in this step. While Huang et al. (1998) and Turcu (2013) pointed out that presently it lacks integration of citizen-led and expert-led approaches, (Liu et al. (2017), Mascarenhas et al. (2015), Shen et al. (2011) and Tanguay et al. (2010) stated that due to confusion and ambiguity in the definition of sustainability there are no universal criteria for sustainability goals. Stakeholder participation is needed in setting goals or outcomes. Goals should be identified according to some universal criteria and based upon local conditions. This step is instrumental in determining the type of indicator selected according to the urban characteristic. For example, poverty reduction might be a universal criterion but the percentage

sustainability indicator frameworks. This is the external resistance that makes selection, interpretation and application of indicators complicated and useless (Moldan et al., 2012). These are characterized by lack of data, policy lethargy or unwillingness on part of the government to implement the indicators, lack of consensus on what constitutes standard indicators and lack of comparative analysis across disciplines and cities. These are the problems that we face during implementation and incorporation of indicators in decision use. 3.1.1. Internal challenges The way sustainable development indicators are developed is a matter of much debate (Turcu, 2013). Development of indicators is many times backed up by unsound methodologies (Mori and Christodoulou, 2012). Top-down or expert-led and bottom-up or citizen-led models are well documented. Bottom-up approaches are suitable for local or regional level studies while unsuitable for global studies where top-down methods are more applicable. A list of challenges innately present in indicators (internal) is given in Supplementary Table S. 1. Here we have discussed the issues and opportunities of sustainability indicators in urban settings according to the steps of indicator framework identified in Fig. 3. Internal challenges are encountered in steps (A) to (E) of the proposed indicator framework. Preliminary assessment (A) is most important before setting the stage for an indicator framework. This is the first step in indicator 287

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Fig. 4. Number of challenges and opportunities of each step in the indicator framework identified for 2006–2017 (refer Supplementary material Tables S. 1 and S. 2).

most recurring indicator in their respective category. Indicator-based indices or composite indices constitute combination of different indicators. Choice or selection of indicators and weighting are the biggest criticisms levelled against composite indices (Tran, 2016). Indices like Dashboard of Sustainability, Environmental Sustainability Index, Environmental Vulnerability Index, Environmental Policy Index, Wellbeing Index, Living Planet Index, Human Development Index and City Development Index are examples of composite indices (Mori and Christodoulou, 2012). But these are plagued by the considerations of how much importance or weight is given to constituent indicators (Pissourios, 2013). Becker et al., (1987) conducted a study in the United States and reported that out of the selected cities 134 could be ranked first, 150 could be ranked last and 59 could be ranked first or last, depending on the weighting scheme (Becker et al., 1987). Welfare indices measure welfare contributions in common monetary units. They provide aggregation of individual indicators using monetary units of measurement, but Pissourios (2013) notes that they lack sound theoretical foundations and even slight changes in weighting method of consumption spending can substantially change the overall value of the index. The selection of indicators determines its aggregation and the different choices made during aggregation will produce different outcomes (Pissourios, 2013). Weights are target group specific because policymakers, citizens, experts and businesses will have different priorities for different issues, therefore how much an indicator contributes to the final index value depends on the subjective understanding of different stakeholders (Ahvenniemi et al., 2017). Indicator selection largely consists of selecting the best indicator according to the objective of development plans, which is quite reasonable. But there is lack of any research on how such objectives can be universally applied according to urbanization characteristics and hence there is absence of any universal indicators according to those urban characteristics. This is a dilemma of the trade-off between universal applicability and relevance of indicators. Setting baseline (D) is a neglected area of indicator assessments. Socio-economic data is usually collected through national or regional sampling surveys on a regular basis while scientific data is collected

reduction of people living below poverty line would be determined by the realistic local conditions and capacity. It was found that the indicator research is bent more towards their selection methodology (Fig. 4). Indicator selection (C) is an iterative process which involves setting the selection criteria, identifying reliable (Huang et al., 1998) indicators with stakeholder participation as an important component. Since most of the research has focussed on this aspect a large number of indicators have been identified with as many numbers of selection criteria and no universally accepted approach. Tanguay et al. (2010) suggested that we may accept the most cited indicator as the most relevant one. This approach has benefits as well as drawbacks. The most cited indicator means that it should be simple, easy to measure with available data (Kumar et al., 2015), but it also means that its simplicity might compromise its ability to measure sustainability dimensions in depth. Further, they proposed that the index should cover all the components of sustainable development and certain predetermined categories which occur pertinently, as given in their study, and the simplest index should be chosen for easier data collection, analysis and dissemination. For measuring sustainability, a conceptual framework is necessary to follow the most appropriate selection criteria for indicators. In order to actualize their recommendations, Tanguay et al. (2010) proposed a SuBSelec strategy for sustainable development indicators. They compared whether selecting indicators cited at least four times and representing more categories of sustainable development was better than choosing indicators cited more than four times but representing less number of categories. The themes of sustainable development were determined by them in order to incorporate a sound conceptual framework in their strategy. They further applied the following three conditions for selecting indicators, first, parsimony in the indicators with easy understanding and usefulness, second, coverage of all categories of sustainable development, and third, retaining indicators on which consensus exists in literature for a sound conceptual understanding. They found that it is better to use lesser number of indicators. Six sustainable development categories out of twenty, which were not represented by the selected indicators were included by adding the 288

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steps are not much researched either and we were not able to identify challenges in respect to these steps. In a top-down approach, the governments have the administrative machinery and will to implement these through publications, public information dissemination as well as numerous government departments to sustain the framework. Decision use of indicator assessments (Applying findings, I) is rare. This aspect has been neglected and it is one of the emerging topics in indicator assessments. Unclear methodologies might give rise to sustainability indices with unsustainable issues (Turcu, 2013). Development of indices continues to be a search for technical and scientific solutions rather than an answer for political and social challenges which includes ethical and moral dimension (Turcu, 2013). Thus, steps D, G, H, I and J need better analysis and inclusion in urban sustainability assessments. The balance between political and social with scientific characteristics of sustainability indices need to be achieved. Generally, a list of criteria for indicator selection and development is easily prepared while the task of such indicator frameworks is hard to accomplish (Ramos & Caeiro, 2010). Universal acceptability and influence on policy making are lacking in all indicator sets (Mori and Christodoulou, 2012). Further, extensive and large-scale studies, such as European Common Indicators developed for European Union, are rare and very expensive (Pissourios, 2013). A very large amount of data has to be gathered which is usually repeated on a timely basis. Such reports quickly lose their relevance with time. A lot of indicator sets are developed with the aim of providing policy directions for the public and government bodies but their sheer numbers and complexity involved in measurement makes them unattractive for real use (Pissourios, 2013). In the United States a study by Gahin et al., (2003), reported that five indicator projects resulted in intangible benefits like sustainability, increased community dialogue, a better understanding of community issues, while the real benefits like policy making and implementation of results were rare (Gahin et al., 2003). Pissourios (2013) holds that publication of such studies seldom makes any policy decision or mobilize public towards sustainability. Studies that cover a broad range of themes cannot do justice to details which are necessary from a policymaking perspective. Such studies cannot link unsustainability to its causes as they are not linked to problems or focussed on certain issues (Pissourios, 2013). Sustainability indicators should have following simple criteria like easy calculation, data availability, commensurability, scientifically determined thresholds, with easy penetrability into policy decisions. This is in accord with the Bellagio principles for assessing progress towards sustainable development (Council, 0000). In this section, we discuss recommendations from various studies for urban sustainability indicators.

through continuous monitoring of environmental parameters. This data needs to be used to create a baseline for gap analysis. Selecting targets (E) requires scientific input to determine the sustainability requirements and stakeholder discussion to determine practicality of targets. Selection criteria needs to be set in this step. This is also an aspect which requires more research to bring out definite threshold values (Fig. 4). Mori and Christodoulou (2012) called for absolute thresholds to reduce the confusion between elements of the triple bottom line and indicate the level up to which the system can function sustainably. Cook et al., (2017) seconded their opinion and included expert judgement and nation-specific analysis for a holistic assessment of environmental indicators. Thresholds are scientifically determined or policy-based targets beyond which the system is considered unsustainable. Threshold hypothesis is basically an ecological economics measurement concept. Basic human needs must be met before holistic development is targeted (Smith et al., 2013) but in practice even after satisfying basic human needs such development does not take place. When macroeconomic systems exceed beyond a certain point the marginal benefits of further growth are offset by the marginal cost of externalities (Pissourios, 2013). As mentioned before, indicators measuring these are called welfare indices which determine the benefits and costs of growth. One of the earliest indices, Daly and Cobb’s Index of Sustainable Economic Welfare (ISEW) was developed in 1989. It studied the trend of GDP and ISEW values and concluded that economic growth is beneficial up to a certain point only, beyond that it becomes detrimental (Pissourios, 2013). Lack of scientifically determined thresholds has been pointed out by many authors (Marletto and Mameli, 2012; Moldan et al., 2012; Mori and Christodoulou, 2012; Shen et al., 2011; Shen and Zhou, 2014). As can be seen from Fig. 4, selection of an appropriate target is an important challenge to be overcome for assessing urban sustainability. 3.1.2. External challenge Tanguay et al. (2010) stated that sustainable development has a broad definition which gives rise to multiple interpretations. Mori and Christodoulou, (2012) associated the same reason to indicators’ weakness and further added the diversity of purposes for measuring sustainability and the confusion of terminology, data and methods applied in measurement as the major causes. External challenges emerge during steps (F) to (J) of the indicator framework (Fig. 3). Application (F) of indicators to gather real information is the most important step of indicator frameworks. It involves the collection of data and results by applying the indicators. Application of indicators is to collect data and results, while application of findings is to implement the information generated from indicators to bridge the gap between sustainable and unsustainable development. Application of indicators has the biggest crucial challenge of data unavailability. Because of the paucity of data, even the most logical and scientific indicators framework would fail. According to Moldan et al. (2012), even if data is available, selection, interpretation and use of indicators is the main difficulty. But as data availability has been identified as a challenge by many authors, we can conclude that it is a very frequent external challenge while applying indicators in actual situation. The issue of commensurability limits the use of indicators and results in another external resistance in the form of lack of comparison between case studies. Evaluation (G) of indicator results include performing sensitivity analysis and identifying short-comings to modify the indicator assessment framework. This is also a neglected step of indicator framework studies (Fig. 4). In an interesting study, Ramos & Caeiro (2010) cited the importance of meta-analysis to evaluate the effectiveness of indicators. They said that very few indicator frameworks implemented had provision for meta-analysis. In the absence of such an evaluation (Li et al., 2009), the credibility and long-term sustainability of the indicator frameworks is jeopardised. Reporting findings (H) and Sustaining the indicator (J) framework

3.2. Outcomes Nations have developed indicators according to their local or national priorities (Shen et al., 2011). While urban sustainability performance is measured across the world, there is no single set of indicators that can be used for all the urban areas (Shen et al., 2011). Common indicators are needed for comparison and ranking between cities and countries. It is important to consider that sustainability indicators serve as a means to an end and are not in themselves the goal of achieving sustainability. Shen and Zhou (2014) identified five principal criteria for sustainability indicator selection, they are, the scope of sustainable development dimension, coherence for strategy, public participation, focus on sustainable development goals and consistency regarding meaning and dimensions of sustainable development indicators. A list of major suggestions come across after a review of recent literature is given in Supplementary material Table S. 2. Tanguay et al. (2010) warned against using Pressure-State-Response models and their derivatives like Driving-Force-Pressure-State-Impact289

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thresholds and a conceptual framework are needed as preliminary considerations for indicator-based evaluation of urban sustainability. While setting a Baseline and finding thresholds (step D), Evaluation of indicator framework after implementation including sensitivity analysis and modifying the framework (step G), and Application of findings in the real world in order to move towards sustainability (step I), are the three emerging issues in indicator-based sustainability research.

Reaction models. They involve multiplying the number of indicators four or five times as each category of sustainable development must consist of pressure, state and response indicators. The PSR model is based on cause and effect relationship between the origin of change and their consequences. Social and economic Drivers, like population growth, exert Pressure on the environment which changes its State such as biodiversity or resource availability and leading to Impacts on human or ecological matrix and anthropogenic Reaction on the Drivers of change (EEA, 1999). The PSR and its derivative were more environmentally focused but they did not address the complex inter-linkages between drivers, state and response, and could not highlight the relationship between indicators and policy relevance (U.N. Department of Economics, 2007). Thus, the PSR model was abandoned from 2006 (Tanguay et al., 2010) and replaced with a theme/sub-theme based flexible model by Commission for Sustainable Development for sustainability indicators (U.N. Department of Economics, 2007). According to Tanguay et al. (2010) environmental and macroeconomic indicators are theoretically and methodologically sounder while quality of life, welfare and sustainability indicators are supported by weak theoretical foundations which leads to methodological inconsistencies. By applying their selection criteria Tanguay et al. (2010) may have been able to overcome this short-coming. Regarding targets, Hák et al. (2016) stated that they should be measurable and accessible by means of indicators (see Supplementary material Table S. 2). Dizdaroglu (2015) stated that indicators should be relevant for making policy decisions, should be analytically sound and measurable. This discussion about sustainability indicators brings forth three important criteria from the challenges mentioned in Supplementary material Table S. 1 and recommendation given in Supplementary material Table S. 2, that is, application of indicators and subsequent assessment of urban sustainability will be most influenced by:

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1. Data availability 2. Target/sustainability threshold (scientifically determined or policy goal based) 3. A conceptual framework for indicator selection Other challenges will have a significant impact on sustainability assessment but the above-mentioned aspects can be considered as the first step to determine simple, or crude, sustainability assessment framework of a city. The theme/sub-theme-based categorisation of indicators across the triple bottom line or four dimensions of economic, social, environmental and institutional sustainability is the most commonly practiced methodology. According to UN CSD (U.N. Department of Economics, 2007) issue and theme-based indicator frameworks are adopted by most countries for national, regional or theme-based sustainability assessments as they are easier to understand and present, and incorporate into the policy framework. It is interesting to note that in our literature review, we were not able to find any work which comprehensively dealt with the relationship of indicators with stage, level or characteristic of urban areas. This issue has been addressed to a certain extent in SDGs by creating a flexible, national priority-based choice of targets but it still lacks the comprehensiveness required to capture the urbanization types and levels. 4. Conclusion There is a large literature on indicator application in sustainable development. Due to the overpopulation of indicators, there is a need to bring out the most important and relevant ones. But in order to select such a simplified indicator system, the major challenges in application and development have to be resolved. This work is a step forward in that direction. We determined the steps involved in indicator framework in order to identify the challenges associated with each step. The major challenges and opportunities were then analysed in respect of each step in the framework. We found that data availability, target or 290

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