Harmonising Indicators to Report Sustainable Development Goals and Sustainable Energy and Climate Action Plan: Systemic Analysis of Existing Regional and City Indicators Sets

Abstract

Balancing economy, social justice, and environmental protection while achieving decarbonisation and adapting to climate change poses a significant challenge for nations, regions, and cities. The Sustainable Development Goals and the Sustainable Energy and Climate Action Plans are widely used plans designed to oversee mitigation and adaptation actions. However, despite the common topics addressed by both, the absence of a common framework and the multiplicity of indicators proposed imply an extra effort in their implementation and evaluation, as well as the difficulty of evaluating peer benchmarking. Hence, this review focuses on identifying frequently proposed indicators, highlighting potential links among metrics and establishing a list of potential indicators. The bibliographic analysis conducted allowed the identification of more than 80 sources and 410 different metrics. The study reveals the diversity of approaches chosen to define a set of indicators and underscores the need for a harmonised framework to effectively compare and monitor European regions and cities. Moreover, thanks to this study, a list of potential indicators and the methodology for populating them was established, allowing better coherence among the initiatives and a starting point for small regional and local administrations that often struggle with the availability of data and resources.

1. Introduction

During the last decades, sustainable development has gained momentum as a key strategic mechanism to conciliate population needs, such as economic growth and social equity, with the effective protection of natural resources and environments. As stated in the last Intergovernmental Panel on Climate Change (IPCC) technical report, the accelerated warming and the intensification of impacts and risks above 1.5 °C warming increases the critical role of the current decade to uphold climate-resilient development pathways that drive the transformation of prevailing development practices and offer the most significant promise and potential for human well-being and planetary health [1].

The World Commission on Environment and Development defined sustainable development in 1987 as a development “that meets the needs of the present without compromising the ability of future generations to meet their own needs’’ [2]. Nevertheless, as pointed out by Robert et al. (2005), there is an inherent ambiguity in the standard definition of sustainable development. This ambiguity has allowed a wide range of disparate groups to align themselves with sustainable development, but it has also led to a proliferation of interpretations and advocacies regarding its true meaning. In some cases, the literature focuses on economic development, while others shift to human development or society development, emphasising values such as security and well-being. Similarly, even though, in 2002, the World Summit expanded the standard definition with the three pillars (economic, social, and environmental), a universal agreement on the specific details of these pillars was not reached, resulting in ambiguities that continue to influence the standards and indicators associated with sustainable development [3].

After these initial statements, many highly recognised international documents and reports have contributed to the advancement of sustainable development [4,5,6,7,8,9]. In this context, the evolution from the Millennium Development Goals (MDGs), which were primarily focused on developing countries [10], to the Sustainable Development Goals (SDGs) [8] has represented a clear step to expand the scope and integrate a wide-ranging vision of sustainable development.

From the beginning of the SDG process, it was clear that localising the SDGs was important to take into account subnational and local contexts in the achievement of the SDGs [11]. Starting from article 28 of Agenda 21, which recognised the importance of actions at the local scale, many of the reports stressed the importance of cities as focal points of growth due to the fact that more than 68% of the population is projected to be hosted by 2050 [12]. While some authors have highlighted their role as pioneers of local transformation, both internally and by leading the overall community [13], others have stated that “The sustainability battle we are fighting is a granular one, and it will not only be won or lost in cities but by cities through a million different decisions” [14]. Similarly, other authors have claimed their role beyond SDG11 implementation, since many of the SDG target activities fall within the responsibility of local governments [15] or the relevance of proper engagement and coordination with local and regional governments to achieve more than 60% of the targets behind the 17 SDGs [16].

This relevant point has led to the creation of several local initiatives aiming to support sustainable urban development, such as the launch of Local Action 21 in Johannesburg in 2002, the foundation of the International Council for Local Environmental Initiatives, which is today called ICLEI—Local Governments for Sustainability [17], the C40 Cities Climate Leadership Group [18], and LOCAL2030 [19].

Local and regional authorities are confronted with significant challenges, many of which originate at the global level but also have local implications and impacts. Rapid urbanisation requires a prompt response to ensure access to housing and essential services like water, energy, and transport. The impacts of climate change are also felt locally, making it vital to develop responsive resilience and environmental strategies. Moreover, creating decent employment opportunities and social cohesion are also policies needed at the local level to prevent social exclusion and poverty [20,21,22,23]. As a consequence, several directives were set in place, starting with the EPBD 2002/91/EC [24] and continuing with the launch of the 2020 Climate and Energy Package in 2007 [25], to meet climate and energy targets. These efforts have been sorted and reinforced through the adoption of the Green Deal in 2019, which established the road map to achieve climate neutrality. In addition to official EU regulations, in 2008, municipalities all over the world launched the “Covenant of Mayors” initiative (CoM) [26] with the aim of fostering the implementation of actions, which introduced the Sustainable Energy Action Plans (SEAPs) and later on the Sustainable Energy and Climate Action Plans (SECAPs). This initiative established a bottom-up approach and congregated local entities to share experiences and capitalise on the knowledge acquired among members. Until 2024, this movement has successfully brought together over 12,500 local and regional authorities, making it one of the most significant collective efforts for local climate and energy actions [27].

With regards to indicators, from an early stage, both the UN initiatives and the EU directives highlighted the need for key performance indicators (KPIs). Chapter 40 of Agenda 21 introduced the necessity of indicators that provided solid bases for decision-making at all levels and contributed to the self-regulating sustainability of integrated environment and development. Since then, a broad range of international indicator frameworks [28,29,30,31,32], as well as local and regional initiatives [33,34,35,36,37,38,39,40,41], have been developed to measure the progress towards sustainable development at different scales, including the adoption of the Agenda 2030 and the development of SDG targets goals and indicators. However, despite these efforts and their relevance, authors have claimed that there is a lack of consensus not only on the approach and conceptual framework but also on the selection and optimal number of indicators, in many cases due to the ambiguity in the definitions of sustainable development [3,42]. Until the publication of this paper, there was no official set of indicators published by the UN to be used at the local level.

As for indicators included in the SECAP mechanism, KPIs related to climate neutrality usually have well-recognised metrics such as final energy consumption or greenhouse gas emissions; on the contrary, adaptation aspects often rely on the criteria established by the authorities reporting these issues.

Beyond the defined frameworks and their indicators, the benefits of defining a common approach seem clear—that is, to establish certain correlations among the most frequently used initiatives (definition, implementation, and monitoring), to optimise the need for resources for medium and small administrations that struggle with budget or other technical limitations, and to facilitate a standardised comparison between regions and cities, thereby easing benchmarking initiatives. In that respect, up to 2024, no official set of SDG indicators at regional and local scales was established, and no common framework assessing the indicators used in SECAPs (as the main instrument of the CoM initiative) and the SDGs has been proposed. As proof of that fact, the initial search on the engine Web of Science using “sustainable development goals”, “indicators”, and “SECAPs” as keywords returned zero results.

Thus, this article conveys the considerations related to, first, the diversity of the set of indicators available at the local level and, second, the potential links between SDG indicators and SECAP mitigation actions in order to align the different measures to be implemented at the local level. Accordingly, our research addresses the following questions (Q):

Q1. Are cities or regions reporting all SDG target goals?

Q2. Are local and regional authorities using the global SDG indicators or introducing new metrics to “downscale” the global framework?

Q3. Are there any common metrics proposed among the different sources, and which are the main themes being addressed?

Q4. Are there any indicators that can be linked to the SECAP and SDG plans and, thus, to the mitigation and adaptation actions present in both mechanisms?

Q5. Out of the most commonly used metrics and considering the link between SECAPs and SDGs, is it possible to define a set of harmonised indicators?

The sections of this paper are organised as follows: after the Introduction, Section 2 presents the SDG and SECAP plans and their relevance at the local level and points to the links between the initiatives; Section 3 analyses the concept of an indicator and its definition in the context of the plans; Section 4 introduces the methodology followed to collect and filter indicators, the case studies, and the set of potential indicators complying with the requested purposes; Section 5 exposes the analysis and results; and Section 6 and Section 7 discuss those findings and summarise the conclusions, respectively.

2. SECAP and SDG Plans

In alignment with the “2020 Climate & Energy Package” [25], which aimed to cut 20% of greenhouse emissions, improve energy efficiency by 20%, and increase renewable sources by 20% by 2020, the European Commission launched the “Covenant of Mayors for Climate & Energy” initiative (CoM) in 2008, intending to gather together local governments committed to achieving climate and energy targets [26]. The initiative has now been extended to municipalities worldwide, with over 13,000 local and regional authorities across 60 countries participating [27]. It is recognised as one of the world’s most significant urban climate and energy policy tools [43,44,45,46]. Specifically, the initiative has gained significant traction in Europe, gathering almost 12,000 signatures by the year 2024 [47], which accounts for more than 80% of the total signatures. Moreover, even though the CoM is based on a voluntary commitment, some regional administrations, such as Barcelona in Spain, Flanders in Belgium, and Lombardi in Italy, have adopted this instrument as a fundamental part of their official climate change strategies and are supporting its implementation with commitment rates higher than 60% [48,49,50,51,52].

The CoM movement is structured in three main pillars: (i) reducing greenhouse gas emissions, (ii) increasing resilience and adapting to climate change, and (iii) tackling energy poverty as a key action to ensure a just transition. It is worth mentioning that even though the three pillars are now integrated into a unique mechanism, the second pillar linked to adaptation actions was not fully integrated into the plans until 2015, and compliance with the poverty pillar is fairly new and will not be mandatory until 2025. Moreover, the initial CoM initiative has been recently updated to consider the objectives of the European Green Deal [53], including the update of energy targets, such as the more ambitious greenhouse gas emissions reduction of 55% by 2030.

To achieve climate and energy objectives, each municipality must present a Sustainable Energy and Climate Action Plan (SECAP), previously called a Sustainable Energy Action Plan (SEAP), within the first two years of joining the initiative and present qualitative monitoring reports every two years and quantitative ones every four years. However, despite the large number of entities committed to the CoM, municipalities face a multitude of challenges, including a lack of resources or limited access to data for defining the baseline and measuring progress. Up to 2022, only 23% of the signatories had presented monitoring reports [54]. In addition, since many municipalities joined the programme before adaptation actions were fully integrated in 2015, many plans and monitoring reports only address mitigation aspects. By September 2016, there were 5767 signatures committed exclusively to the 2020 mitigation targets [55].

A large number of documents can be found explicitly addressing SECAP and SEAP challenges and barriers over the years, such as the complexity of assessing the adaptation pillar and the long-term benefits of actions at a local level [56], the lack of knowledge and resources [44,56,57], the absence of a final monitoring report, the heterogeneity of data used, the low number of intermediate monitoring reports submitted [58], and the lack of political interest in implementing and monitoring the plans after the initial commitment [44].

Nevertheless, despite its challenges, many authors have recognised it as a potential tool not only to reduce and track GHG emissions but also to design long-term strategies [43,55,59,60,61,62], highlighting that this kind of transnational initiative might prove particularly effective in supporting the voluntary alignment of local communities to European climate and energy targets [63]. In light of these considerations, the potential role of the Covenant of Mayors initiative and of the related Action Plan has gathered a rather widespread interest [64,65], first, as an instrument providing a standardised framework and methodological guidelines to set targets and develop plans [66] and as a database of information at the local level [67]. Moreover, thanks to the significant participation of cities, many articles can be found analysing the impact of the implementation of SECAPs, the policies implemented, and their effectiveness in reducing CO₂ emissions [58,59,60,61].

In relation to the SDGs framework, the instruction to develop the SDGs was included in the Rio de Janeiro Conference, ‘The Future We Want’ [7], which incorporated the request to create an Open Working Group (OWG) to develop the set of goals. The SDG “zero draft” was adopted by the OWG in July 2014 [68] and was endorsed in the autumn of 2014. The SDGs were built based on the lessons learned from three indicator sets: the Millennium Development Goals (MDG), which included a total of 60 indicators [10], the Sustainable Development Indicators of the European Statisticians Conference (CES SDI), which included a set of 90 indicators [69], and the SD Solutions Network, which contained 100 indicators [70].

In September 2015, United Nations member states adopted the Post-2015 Development Agenda for Sustainable Development. This agenda contained 17 sustainable development goals (SDGs) and 169 related targets. The goal was to achieve sustainable development by 2030, considering five different areas: (i) people, (ii) planet, (iii) prosperity, (iv) peace, and (v) partnership, integrating the three dimensions of sustainable development (environment, economy, and social). The 2030 Agenda called for the action of all global actors to jointly achieve these goals, pledging that none will be left behind [8]. To this end, the instrument, which was intended to be monitored at the national level, was disaggregated into 169 targets and 248 indicators. In fact, it comprises 231 unique indicators since 13 of those were repeated under two or three different targets.

Nevertheless, although Agenda 2030 encouraged countries to “conduct regular and inclusive reviews of progress at the national and sub-national levels, which are country-led and country-driven” [8] and called for cross-sector collaboration, the monitoring of SDGs at the national level has been mainly done in two forms: (i) international reporting using the official list of UN indicators and data and (ii) Voluntary National Reviews (VNRs) where the progress is explained in more detail. At the local and regional levels, the reporting has been done using the structure proposed in the Voluntary Local Reviews (VLRs) and the Voluntary Regional Reviews (VRRs). Up to 2023, 189 member states had presented at least one Voluntary National Review [71], whereas, only 240 VLRs had been presented and 37 VRRs [72]. Despite the low number of VLRs, several authors have stressed their importance, first as an urban planning instrument to facilitate a dialogue between stakeholders, analyse the gaps connecting cities, and share information [73] and also as a framework to conduct comprehensive assessments and foster a more cohesive sustainability management [74,75,76].

Additionally, at the city scale, beyond the specific introduction of SDG11 in recognition of the city’s critical role, UN-Habitat established in 2016 the New Urban Agenda (NUA) [9] and has subsequently promoted actions to localise and complement the global indicator framework [77,78,79]. Nevertheless, despite the UN-Habitat efforts to foster the implementation of SDGs, many authors argue that SDGs are often vaguely formulated and in need of local contextualisation [80,81,82,83]. Some authors emphasise the challenge of monitoring a large number of indicators since often complementary metrics are required to address specific aspects at the city level [84]. Others point out that while SDGs can be relevant for urban authorities, it is essential to have comparable, reliable, and robust data to become effective policy tools and ensure the monitoring of sustainable development [33,36,85,86,87].

To fill those gaps, an increasing amount of research dealing with the localisation of the SDGs at subnational and local levels can be found [11,34,39,88,89,90,91,92,93,94,95,96,97,98,99] not only addressing Goal 11 but also contributing to a large number of SDGs, and although some authors claim that a “one fits all” approach does not adequately represent the reality of cities [100], many other authors claim that it is essential to maintain strong common metrics in measuring performances in relation to the 2030 Agenda to compare the results of the effort performed by the municipalities in a rigorous way [33,86,87,101].

In regards to the analysis of the structures of both plans, several papers can be found advocating for the need for further integration and a more systemic approach to the SDGs [92,102] and a great number of papers exploring the interconnections between goals, targets, and indicators included in the instrument [75,102,103,104,105,106,107,108]. Along the same line, some authors have explored the interconnection of the SDG framework with other previously existing urban frameworks. Tanguay et al. (2010) analysed the interconnection between SDGs and 23 previously developed urban sets [42], Zinkernagel et al. (2018) evaluated the progress of sustainability in cities by exploring the links between SDGs and seven indicator sets developed by transnational, non-private organisations [84], and Merino-Saum et al. (2020) methodically analysed 77 sets of indicators using the SDGs as an analytical framework to analyse the metrics [109].

Specifically regarding the interactions between local SDG implementation and SECAPs, some documents were found citing the interactions between them. UN-Habitat (2020) pointed out the relationship between the CoM initiatives and SDG13 related to climate change [78]. Ihobe Sociedad Pública de Gestión Ambiental (2019) pointed out the links with SDG03, SDG07, SDG11, and SDG12 [110]. Additionally, one particular paper can be highlighted, exploring in more detail the interconnections between regional plans aligned with SDGs and municipal actions planned under the umbrella of the CoM [43].

Yet, despite both plans addressing common topics such as mitigation, adaptation, and energy poverty, as shown in Figure 1, to the best of our knowledge, no paper can be found exploring in detail the interconnections between the set of indicators adopted in local SDG implementation and the SECAP framework and considering not only theorical frameworks but real implementation by cities. As an example, as observed by Colocci et al., 2023 [43], more than half of the regional Italian interventions developed considering sustainable development had a clear correspondence with the municipal actions planned under the umbrella of the CoM. This considerable overlay detected suggests that consistent coordination of SECAPs with other local and regional planning tools is needed to maintain coherence between regional and local levels and to overcome current limitations [43].

3. Indicator Assessment of General Concepts

Indicators can be either science-driven, therefore based on non-subjective theoretical models, or value-driven, where the indicators reflect current social debates and priorities [84] and are conceived as technical plans based on available and reliable data that assist decision-making processes or as message carriers, allowing the definition of the different arguments or ideas not only from the technical perspective but also involving political and normative aspects [109]. Hence, indicators can be defined as observable variables that provide evidence of a certain condition, either that one exists, that there is a trend in a particular direction, or that a specific condition has been achieved [111,112].

In addition, the process of developing an indicator set for sustainability faces several tensions, such as parsimony vs. comprehensiveness, which can be evidenced in the variation in the choice and number of indicators to assess a key aspect properly: context specificity vs. general comparability expressed as the dichotomy between adopting indicators that consider local specificities or using internationally standardised indicators and complexity vs. simplicity embodied by the necessity to balance scientific credibility with a suitable level of understandability for all involved stakeholders [109]. Moreover, considering the range of aspects covered by sustainable development, selecting indicators can be challenging, particularly for aspects linked to the social or to well-being, which frequently involve estimating unobservable variables. In order to have reliable information, a clear methodological and theoretical work needs to be established [111].

Moreover, concerning local implementation, some authors claim that indicators need to be relevant, acceptable, and practicable and that the number of indicators chosen needs to be high enough for policy relevance but low enough for feasibility in terms of cost and effort [85]. Others, as stated before, advocate for a set of integrated metrics with a holistic approach to foster the dialogue and participation of a range of actors in integrated planning [113].

Over the past few decades, many indicators have proliferated to monitor and assess the performance on several aspects, such as sustainability, well-being, quality of life, or urban services, at different scales and for different purposes. Sustainable development indicators were introduced in Chapter 40.4 of Agenda 21 as the means to “provide solid bases for decision-making at all levels and to contribute to a self-regulating sustainability of integrated environment and development systems” [114]. In that sense, Nations to Cities have been using indicators to assess the three pillars of sustainable development, environmental conditions [115], and social fairness [4], as well as economic development [116].

Despite Agenda 21 calling for appropriate indicators, there is no current consensus among the different programmes on how to measure sustainable development [117]. Several studies and reports can be found that analyse the attributes of the conceptual frameworks used to define and select indicators [42,118,119,120]. Similarly, several papers were found discussing the need for localisation considering that SDGs were conceptualised at the national level, and therefore, on many occasions, the metrics chosen were unavailable, inappropriate, or inapplicable at the local scale [94,121].

In view of these problems, recent research and, to a greater extent, grey literature, many attempts by international organisations [28,32], regions, and cities [98,122] have been made to develop a set of indicators to monitor sustainable development. The abundance of initiatives proliferated to the extent that some authors named it an “indicator industry” [119].

Concerning the indicators selected for SDGs, the framework is structured around 231 global indicators. Nevertheless, at the local level, there is no specific consensus, and many local and regional governments develop their own specific contextualised framework. There have been some intentions to develop a more standardised set of indicators, such as the indicators for European cities to assess and monitor the UN Sustainable Development Goals (SDGs) [123] or the SDG Index and Dashboards Report for European Cities [124] or the OCED web tool at the international level, and some regional attempts, such as the Local Indicators for the 2030 Agenda from Flemish municipalities [98] and the Sustainable Development Goals in 100 Spanish cities [33]. In addition, there is an overwhelming number of local frameworks developed by city administrations [40,97,125,126,127,128].

Still, there are challenges when it comes to adapting the SDG targets and indicators to each administration’s unique context, such as the availability of data, the lack of strong data collection institutions in the city, the complexity of the coordination and contextualisation of the goals considering the diversity of actors involved and the reality of different cities, or the lack of capacity, skills, or funds to allocate to this task [84,86,87,93,94,100,101,129]. Moreover, these challenges can be reflected in the disparity of information presented in the Voluntary Local Reviews. Only one-third of the European VLRs presented during 2019/2020 included statistics and detailed information on the framework chosen. The majority of them used indicators specifically designed by the institutions in charge, and only about 42% adopted indicators from existing national datasets [89].

On the other hand, regarding the CoM initiative, mitigation indicators are defined in the programme’s templates and guidelines to provide clear accountability for greenhouse gas emissions in what is called the Baseline Emission Inventory. On the other side, and for the other two CoM pillars, adaptation and energy poverty indicators depend solely on the authorities creating the plans, making benchmark analysis complex due to the different indicators introduced by each administration.

Given the context provided and the importance of creating a specific set of SDG indicators for local and regional areas, this paper aims to assess and evaluate existing SDG indicators from international organisations and local governments. The goal is to align these indicators with the SECAPs framework, recognising the significance of identifying and addressing local and regional needs in sustainable development. The aim of the study is not only to identify synergies but to develop a universal, harmonised set of indicators for both SDGs and SECAPs that can be a starting point for municipalities with a lack of adequate resources and capacity to take on the functions required to effectively localise the SDGs (particularly strengthened planning and financial and data management capacities) and would enable cities and regions to monitor their actions, conduct benchmark analyses, and optimise resource utilisation [33,86,87,96,101].

4. Research Approach

As stated above, plenty of indicator sets and frameworks have proliferated over the years to monitor sustainable development. Scientific papers and grey literature, such as local reports, were considered to collect a representative sample of local indicators. To gather an appropriate sample of the reports developed over the years, the research was conducted using a five-step approach. As seen in Figure 2, step 1 included the initial search of the terminology on appropriate engines and networks using the PRISMA approach [130]. Academic literature was identified by conducting a data search on the Web of Science electronic database and completing the search by identifying relevant articles cited in the literature found in previous searches. Additional grey literature was found using the Google Scholar engine and the author’s professional networks. Second, documents were listed and filtered according to the scope and granularity required for the study (steps 2 and 3), and lastly, some relevant cases were chosen to conduct the analysis and the establishment of a potential set of key indicators that could boost the implementation and monitoring of SDG and SECAP plans (step 4).

It is worth clarifying that this paper does not intend to debate which areas are covered or how this aligns with the often ambiguous concept of sustainable development. The study is limited to the aspects already established by the SDG and SECAP frameworks, the synergies between both, and how these could be stated by establishing a set of harmonised and universal indicators.

4.1. Initial Search and Selection of Case Studies (Steps 1, 2, and 3)

As stated before, during the first step, the scientific literature was identified through a systematic literature review using the search engine Web of Science (https://www.webofscience.com/wos, accessed on 8 January 2024) due to its broad coverage of sustainability journals. The search was conducted using “Sustainable Development Goals indicators” and “SDGs Indicators” as keywords in the title, complemented by “cities” and “indicators” in all fields, which yielded 80 results; two additional searches were conducted using “Sustainable Development Goals” and “SDGs” as keywords in the title and refined with the terms “localising” and “localizing” to obtain studies focused in the experiences gained during local implementation. The searches returned 6 and 16 results, respectively.

Regarding the grey literature, the approach to identify local indicator frameworks was conducted using the Google engine in combination with other complementary strategies to detect relevant reports. The Google search engine enabled the identification of a significant number of reports related to Voluntary Local Reviews and initiatives that gathered information around the subject, such as Local2030 [19], United Cities and Local Government (UCLG) [131], Sustainable Development Goals Knowledge Platform [132], and the Thematic Research Network on Data and Statistics of the Sustainable Development Solution Network (SDSN TRENDS) [133].

Lastly, other initiatives were uncovered through references in scientific articles or institutional reports and the authors’ professional networks. As a result, 83 additional reports and relevant platforms were included in the analysis.

Subsequently, following the PRISMA methodology process, and as part of step 2, all identified documents and online platforms (102 + 83 = 185) were filtered according to the following criteria: (Filter 1) analysis and development of indicators to be implemented at a regional or local scale (considering local SDG and SECAP focus); (Filter 2) studies focused on the analysis of the overall SDGs framework, therefore, in more than one specific goal. The application of the filters yielded a final sample of 120 documents and 24 platforms.

After identifying the resources whose scopes and contents were aligned with the aim of the study, during the third step, the sample was sifted with a second set of filters to select the exemplary cases to conduct the analysis. The aim of the second filtering was to identify the most representative frameworks and ensure that the content introduced was sufficient to conduct the analysis and that the scope fit the intentions of the study.

The cases were chosen based on the following criteria: documents that provide detailed information on local or regional indicators selected for all SDG targets (First Criteria). Frameworks developed by different institutions, ranging from non-governmental institutions at the international level to guidelines defined at the national and regional levels, were tested for a large sample of cities. Additionally, to account for local contextualisation, exemplary frameworks developed by a specific city or region were included as well. Even though a great majority of the initially considered documents were somehow related to SDGs implementation, the thematic addresses varied considerably.

As shown in Figure 3, three different categories of sources were identified: general assessment or discussions, detailed indicator analysis, and repositories of information or databases (the inner circle). As for the content, the distribution of those sources is represented in Figure 3, first, according to the type of source (the inner ring) and, second, according to the proportion of sources that dealt with a specific aspect or SDG or with the entire framework (the two outer rings). The outermost ring reflects the most relevant recurrences among each subtype of source reflected in the middle of the graphic; since sometimes the sources complied with more than one aspect, the totals reflected can add up to more than 100%. Almost 40% of the documents found were general assessments of discussions that did not analyse the implementation of indicators in detail. Some authors reflected on the challenges or obstacles of implementing SDGs or the localisation of the national framework [11,20,39,73,86,94,96,134,135]. Others analysed the framework but considered the official SDGs framework scope design for national reporting [103,134,135,136,137,138], and others explored the relation of concrete SDGs with some specific actions or planning aspects [113,136,137]. In addition, some of the authors discussed the link of SDGs with specific areas such as well-being, buildings, agriculture, or food [138,139,140,141]. The scope of the sources that analysed indicators more in-depth also varied; 40% of the documents dealt with specific SDGs, mainly SDG11, since it primarily focused on cities [121,142,143,144,145], but also with other SDG goals and targets [136,146,147,148,149,150,151,152,153,154,155]. Only 60% of the sources that analysed indicators addressed the entire framework. In the case of repositories, all were platforms that, in the great majority, offered guidelines or datasets, such as the LOCAL2030 initiative.

In relation to the scope, as seen in Figure 4, most of the literature found intended to influence the international community, and only a small proportion discussed specific aspects relevant only to a city or a region. The outer rings reflects the distribution among each category in the inner circle. In general, this granularity was homogenous among sources, with the international assessment being the most frequent scope in all categories, as can be seen by the outer circle of the figure. Lastly, regarding the level of detail and considering only the documents that either defined or studied a complete set of indicators for SDGs, only 24 of the sources had sufficient information to conduct the analysis; from these, and considering their relevance and scope of action, eight cases were selected.

From the international scope, three relevant reports were selected:

▪

The European Handbook for SDGs Voluntary Local Reviews [156], as it was developed at the European level and is a relevant example of the suggested indicators by international organisations. The document contains a detailed guideline to implement SDGs at the local level, a set of 45 official indicators, and 26 experimental indicators. The indicators proposed were gathered from international institutions and considered the use of recognised databases.

▪

A tool developed by the Organisation for Economic Cooperation and Development (OECD) [28], since it set up an ambitious programme to territorialise the SDGs. It has a database of over 600 municipalities and other subnational authorities.

▪

The report Indicators for European Cities to Assess and Monitor the UN Sustainable Development Goals [123], since it has an extensive analysis of the link between SDGs and 30 existing urban indicator sets listing more than 2000 possible indicators, and it could allow an extensive comparison of indicators with urban frameworks recommended by recognised institutions. Among the databases included in this document are the City Prosperity Index, the City Development Index, and the ISO 31120 and other regional proposals such as the indicators for municipalities in Germany [32,41,116,157].

In addition, three regional representative framework cases were selected to consider indicators suggested by regional associations at, therefore, the sub-national level:

▪

The report Local Indicators for the 2030 Agenda (Sustainable Development Goals) [98] developed as a manual for Flemish cities and municipalities since five of the provinces are at the forefront of SDG implementations, with more than 120 local governments signing commitments [158]. The associated documents and tools thoroughly describe the indicators chosen and are meant to guide almost 300 local governments.

▪

The second edition report of The SDGs in 100 Spanish Cities [33] developed by the Spanish Network of Sustainable Development (REDS) and tested in 100 cities with over 80,000 inhabitants representing all regions in Spain.

▪

The framework proposed by the Province of Barcelona to monitor the progress of SDG goals in the region [122], since it is a relevant example of what targets regional authorities are prioritising and comparing. The framework gives an overview of the indicators and targets selected for 311 municipalities.

Finally, two specific local frameworks were included to account for real local implementation:

▪

The indicator framework developed by the city of Barcelona [126,159], since the city has been at the forefront of the SDG localisation movement for years and has one of the most advanced VLR laboratories in terms of methodological rigour and technical commitment to data collection and management [89]. The framework has an extensive analysis of indicators and a publicly available database.

▪

The indicator set proposed by the city of Los Angeles [127]. Although it was outside the original scope of the study, which was focused on European territory, the latter was included due to its long experience developing and implementing VLRs. Los Angeles City developed one of the first VLRs and is a member of the Brookling SDG leadership city network [99] and has developed a prototype of 39, which could be a good starter kit for cities that are nearly beginning the process.

As shown in Figure 5, the chosen reports range from international frameworks to concrete methodologies elaborated to guide a specific administration, covering not only a significant part of the territory but also representing different contexts and realities. The case studies selected allowed for the examination of different approaches, including those recommended by international associations and methodologies implemented by specific actors in their respective contexts.

4.2. Indicator Selection (Step 4)

After compiling the information, the reports were contrasted with the SDG global framework to verify the alignment between the proposed global indicators and the local adaptation. In parallel with that task, official CoM indicators were then listed and compared with the ones defined in the different SDG frameworks to identify synergies between the two plans.

The initial analysis identified 745 possible indicators, with up to 35 different proposals to monitor a specific target. As for the SDG targets and goals covered, the 8 selected cases yielded a total of 68 targets corresponding to 102 SDG global indicators addressing mitigation and adaptation actions or social and business aspects.

To select the list of potential local indicators, five filters were applied as a fourth step; as an example, Figure 6 illustrates the process using target 7.1. Indicators that complied with at least one of the following criteria were identified as potentially suitable metrics: (F1) indicators that were proposed by more than one source to monitor the same target; (F2) indicators that were linked to more than one target; (F3) indicators that were either constructed or based on metrics reported in SECAPs; and (F4) indicators that could be constructed using open data sources such as Eurostat. Furthermore, since the task aimed to identify indicators for all European regions, all indicators based on locally developed surveys were discarded. Particularly in the case of the Maio et al., 2020 [123], report, due to the large extension of possible indicators, only indicators with more than one reference source were included in the study. Indicators with a single source were considered only when no indicators were found with more than one source for a particular target.

From the initial list and after applying the four filters, 410 potential indicators were listed, with 114 unique indicators after registering repetitions between authors and multiple associations with targets.

5. Results

5.1. Assessment of SDGs at Local and Regional Levels

This first part of the results refers to the initial research question—hence, the level of SDG reporting by local and regional administrations. Considering the 68 targets included and linked to each of the 17 SDGs, local and regional frameworks reported between 23 and 59 targets—therefore, between 34% and 87% of the SDG official targets. Only two targets were listed in all documents: target 1.2 related to poverty and target 3.6 related to traffic deaths and injuries. Target 8.3 assessing unemployment, on the other hand, was either already incorporated in the framework or being analysed for future implementation. Oppositely, Target 13.b, related to climate change planning in the least developed countries and small islands, was not included in any of the case studies, and four targets—2.5: local breeds at risk of extinction, 7.b: installed renewable energy in developing countries, 12.1: sustainable consumption and production patterns, and 13.a: aiming at mobilising sources to address the needs of developing countries—were included in only one source. Targets related to goal 17, addressing global partnership for sustainable development, were, in general, not addressed by the sources since many of the indicators refer to countries and, thus, are beyond city limits.

5.2. Link between Global SDGs Framework and Regional or Local Frameworks

Regarding the second question of the research, each set was analysed to verify the alignment between the global SDGs framework and the indicators proposed at the local level. As can be seen in

Table 1. Alignment between global and local SDG indicators and reporting states.

Number of Indicators. Equivalence and Reporting State	City Scope		National–Regional Analysis			International Analysis
	Barcelona	Los Angeles	Flanders	Province of Barcelona	100 Spanish Cities	OECD	European Handbook	Indicators for European cities
Reported and equivalent to the global UN indicator	6	34	2	2	3	5	3	9
Reported but different from the global framework	57	34	62	27	42	31	34	69
Total reported	63	68	64	29	45	36	37	78
Pending to report. Currently analysing how to report it	14	17	-	-	-	-	-	-
Not reported	25	17	38	73	57	66	65	24

, indicators were listed and compared with the official SDGs indicator list, first to establish if all indicators were reported at the local level or if there were some areas either not reported or pending to analyse and second to establish which indicators were equivalent to the global framework and how many were local adaptations.

The analysis showed that there is little alignment between local frameworks and the proposed UN indicators. Official SDG indicators represented up to 33% of the total sets. Oppositely, alternative indicators, introducing a wider range of monitoring possibilities, were up to 68% of the total frameworks proposed in the studies. As for the total number of indicators established in the sets and setting aside the extensive documents comparing the 30 international indexes, the European Handbook and the OECD frameworks comprised a small number of indicators. The same approach can be identified in some of the regional studies, which intended to reduce the complexity of the exercise and select a few comparable indicators to monitor the progress among cities; this is the case of the assessment done in Spain. The median of indicators proposed in regional and international sources was 37, with the Flanders report being the only document that proposed a larger sample of indicators, 61% of which were local adaptations. Oppositely, city frameworks included a more extensive set of indicators, with 63 in the case of Barcelona and 68 for Los Angeles city. Nevertheless, the approach chosen differs significantly; the Los Angeles assessment is closely aligned with the global framework, with a total of 34 indicators that were equivalent to the SDG global framework, whereas Barcelona city’s used only six global indicators, and 56% were local adaptations to consider the specific reality of the city. The same approach can be identified in several other Voluntary Local Reviews; ultimately, as analysed by Ciambra, A., about 52% of all used indicators in European VLRs are local or originally designed by the institutions in charge of the assessment [89].

5.3. Alignment between Case Studies and Common Topics Addressed

As for the third question and the indicators integrated into local frameworks, as shown in Figure 7, four indicators were assessed by all studies or are being analysed to verify their implementation: 1.2.1 and 1.2.2 are associated with poverty, 3.6.1 is linked to death and traffic injuries, and 8.3.1 is related to employment. Furthermore, 55 indicators, 53% of the total sample, were listed in at least four sources and the rest in three or fewer documents. On average, indicators belonging to SDG02, SDG03, SDG12, SDG15, and SDG17 were the least assessed in the frameworks, while all the other goals were present in more than half of the samples. Nevertheless, not all aspects of the goals were addressed in the sets; as an example, even though, in general, indicators related to SDG10 and SDG13 were present in 50% of the documents, they also had some indicators that were not addressed in any of the documents. Furthermore, considering only the four smallest sets, 36 indicators of the total sample analysed were not included in any frameworks. The least assessed indicators in these sets are linked to SDG11 and SDG17. Surprisingly, even though SDG11 specifically addresses cities, fewer indicators were assessed, and 64% of the indicators comprehended in the goal were absent in all the smaller sets.

As mentioned above, most of the indicators proposed by the studies constitute adaptations of the global framework or new metrics proposed at the local level. In addition, the analysis showed that between 1 and 32 different proposals were listed to monitor each target. Consequently, it can be concluded that there are several approaches to monitoring each target. Nonetheless, some common metrics can be identified, such as measuring energy production and consumption for target 7.2. In addition, even though several variables were detected after applying the filters listed in step 4, several metrics were discarded, leaving a maximum of 23 alternatives to monitor a target. Nine targets, on the other hand, did not comply with any of the filters proposed; hence, no potential indicator was identified in the filtered list.

5.4. Set of Potential Indicators and Areas Covered

5.4.1. Complete Array of Potential Indicators

Finally, as for the fourth and fifth questions, the analysis yielded a total of 114 potentially relevant indicators that were either proposed by several sources, linked to more than one SDG target, or associated with the SECAP mitigation pillar. A total of 53 of those were proposed by more than one source and therefore complied with the first filter; 65 could be linked to more than one target, hence, the second filter, and 22 with the third filter, which related SDGs to the SECAP pillars.

As for the goals covered, as pointed out in Figure 8, 13 of the 17 goals and 50 out of the 231 targets are covered—hence, 20% of the official SDGs framework. SDG11, Sustainable Cities, is by far the most represented one with 40 potential connections, followed by SDG13, Climate Action, and SDG07, Clean Energy, with 23 and 18 potential links, respectively. As for the themes included, there are several areas represented from social aspects such as poverty, social housing, or unemployment to air quality, emissions, renewable energy, or current vulnerability to climate change. Planning, land use, waste, industry, and innovation are also among the themes covered by the indicators listed. Moreover, indicators addressing equality and participation are also present in the set.

Furthermore, between one and three associations between targets were identified, mainly between SDG01, SDG07, SDG11, and SDG13, which have clear links to citizens and cities, energy, and climate change. Nevertheless, other connections were identified with goals, such as SDG03, which addresses health and well-being, SDG09, which focuses on industry, innovation, and infrastructure, and SDG12, which assesses responsible consumption and production.

As for the number of sources that incorporated the different indicators, the ones addressing the ratio between housing cost and income were the most recurring ones, followed by the Gini coefficient. Other indicators related to energy and renewables, percentage of women in public organisations, employment and education, access to services, agricultural areas, business registration, public transport, pollution, or waste were also mentioned by several sources. The full final list of indicators and their links with SDGs can be found in Appendix A,

Table A1. Full list of potential indicators.

Indicator	Filter Complied	SDGs Goal	SDGs Related Target
Population at risk of poverty social exclusion or after social transfers	LOT, PSS, LTS	SDG01	1.1, 1.2
		SDG10	10.2
High poverty rate	LOT, LTS	SDG01	1.1, 1.2
Child poverty rate	LOT, LTS	SDG01	1.1, 1.2
People living in households with very low work intensity	LOT, LTS	SDG01	1.2, 1.4
Population living below the national poverty line	LOT, PSS, LTS	SDG01	1.4
		SDG10	10.2
Social housing availability or share of social rental housing in the municipality	LOT, LTS	SDG01	1.4
		SDG10	10.2
Budget dedicated to social services	LOT	SDG01	1.4
		SDG11	11.1
Social/affordable homes delivered	LOT, PSS, LTS	SDG01	1.4
		SDG11	11.1
Housing cost overburden where the total housing costs represent more than 40% of the total disposable household income	LOT, PSS, LTS	SDG01	1.4
		SDG11	11.1
Ratio of the median free-market price of a dwelling unit and the median annual household income	LOT, PSS, LTS	SDG01	1.4
		SDG11	11.1
Citizens’ satisfaction with the local community/municipality with regard to standard of housing and its availability and affordability	LOT	SDG01	1.4
		SDG11	11.1
Social/affordable housing rate	LOT, LTS	SDG01	1.4
		SDG11	11.1
Creation of new subsidised affordable housing	LOT, LTS	SDG01	1.4
		SDG11	11.1
Family expenditure on housing amounts to at least 30% of their family income	LOT, LTS	SDG01	1.4
		SDG11	11.1
Number of deaths, missing, directly affected persons attributed to disasters	LOT, PSS, LTS	SDG01	1.5
		SDG11	11.5
		SDG13	13.1
Population exposed to flood risk, flood prone population	LOT, LTS	SDG01	1.5
		SDG06	6.4
		SDG11	11.5
Disaster Office of Emergency Services Administered Costs	LOT, LTS	SDG01	1.5
		SDG11	11.5
Adoption and implementation of local disaster risk reduction strategies in line with national disaster risk reduction strategies	LOT, LTS	SDG01	1.5
		SDG11	11.b
		SDG13	13.1
Implementation of risk and vulnerability assessments for disaster mitigation addressing natural and human-induced disasters and hazards	LOT, LTS	SDG01	1.5
		SDG11	11.b
		SDG13	13.1
Adoption and implementation of a disaster risk reduction strategy in line with the Sendai Framework for Disaster Risk Reduction 2015–2030.	LOT, LTS	SDG01	1.5
		SDG11	11.b
		SDG13	13.1
Proportion of agricultural area under productive and sustainable or organic agriculture	LOT, PSS, LTS	SDG02	2.4
		SDG14	14.1
Presence of regulations supporting biodiversity, soil and ecosystem health, and/or regulating use of chemical inputs/sustainable farming practices	LOT, LTS	SDG02	2.4
		SDG14	14.1
		SDG15	15.5
Crop area by municipality	PSS, LTS	SDG02	2.4
Traffic accidents with deaths	LOT, PSS	SDG03	3.6
		SDG11	11.2
Traffic accidents with victims (injuries and deaths)	LOT	SDG03	3.6
		SDG11	11.2
Death rate due to road traffic	PSS	SDG03	3.6
CO2 emissions from households, tertiary, and industry	LOT, LTS	SDG03	3.9
		SDG09	9.4
		SDG13	13.3
CO2 emissions from homes, transport, and the tertiary sector	LOT, LTS	SDG03	3.9
		SDG09	9.4
		SDG13	13.3
Population exposed to harmful environmental noise	LOT	SDG03	3.9
		SDG11	11.6
Share of population exposed to total noise values of Lden, Lnigth	LOT	SDG03	3.9
		SDG11	11.6
Population exposed to total noise values of Lden above 55 dB(A)	LOT	SDG03	3.9
		SDG11	11.6
Population exposed to total noise values of Ln (night noise indicator) above 55 dB(A)	LOT	SDG03	3.9
		SDG11	11.6
Deaths from infectious diseases of the respiratory system	PSS	SDG03	3.9
Proportion of women in the city council	PSS	SDG05	5.5
Ratio between men and women in administrative and political positions	PSS	SDG05	5.5
Proportion of women in decision-making posts in companies	PSS	SDG05	5.5
Effort rate of domestic users for the payment of water	LOT, PSS, LTS	SDG06	6.1, 6.2
Proportion of population connected or using safely managed drinking water services	PSS, LTS	SDG06	6.1
Total drinking water consumption	LOT, LTS	SDG06	6.1, 6.4
Water consumption for all domestic uses	PSS	SDG06	6.4
Soil sealing	LOT, LTS	SDG06	6.6
		SDG11	11.3
		SDG15	15.3
Change in water bodies	PSS, LTS	SDG06	6.3, 6.4
		SDG15	15.1, 15,3
Proportion of population with access to electricity	PSS, LTS	SDG07	7.1
Number of charging outlets available for cars owned privately in the public space	LOT	SDG07	7.1
		SDG09	9.1
		SDG11	11.2
Proportion of population with access to electricity	PSS, LTS	SDG07	7.1
Percentage of renewable energy production	PSS, LTS	SDG07	7.2
Energy consumed locally generated using renewable resources	PSS, LTS	SDG07	7.2
Installed power (kW) per technology eligible for green certificates	LTS	SDG07	7.2
Energy generated locally from renewable resources	LTS	SDG07	7.2
Percentage of total electricity production that comes from coal	LTS	SDG07	7.2
Percentage of total electricity production that comes from fossil fuels (natural gas and oil, excluding coal)	LTS	SDG07	7.2
Final energy consumption by sector and fuel	LTS	SDG07	7.2
Renewable energy on the total energy consumed in households and the tertiary sector	LTS	SDG07	7.2
Proportion of the electricity consumed in the city that comes from renewable sources	LOT, PSS, LTS	SDG07	7.2
		SDG12	12.2
Final energy consumption in homes including all types of energy	LTS	SDG07	7.3
Final energy consumption of public buildings per year	LTS	SDG07	7.3
The energy consumption of households for heating	LOT	SDG07	7.3
		SDG13	13.3
Energy recovery from solid municipal waste	LOT	SDG07	7.3
		SDG09	9.4
		SDG12	12.5
Final energy consumption in homes including all types of energy	LTS	SDG07	7.3
Final energy consumption of public buildings per year	LTS	SDG07	7.3
Final energy consumption in homes including all types of energy	LTS	SDG07	7.3
Signature Covenant of Mayors	LOT, LTS	SDG07	7.a
		SDG11	11.b
		SDG13	13.1, 13.2
Unemployed youth rate	LOT, LTS	SDG08	8.3, 8.6
Unemployment rate	LOT, PSS, LTS	SDG08	8.3
		SDG10	10.2
Increase the total number of new businesses in targeted industry sectors over time	LOT	SDG08	8.3
		SDG09	9.2
Firm creation rate (%)	PSS	SDG08	8.3
3-year survival rate of firms (%)	PSS	SDG08	8.3
New business registration	LOT, PSS	SDG08	8.3
		SDG09	9.2
CO2 emissions generated by the commerce sector	LTS	SDG08	8.4
Percentage of young population (from 18 to 24 years old) not in education, employment, or training (NEET)	PSS, LTS	SDG08	8.5, 8.6
Households with internet access	PSS	SDG09	9.1
Satisfaction with level of public transport services	LOT	SDG09	9.1
		SDG11	11.2
Public transport network	LOT	SDG09	9.1
		SDG11	11.2
Performance of public transport network, ratio between accessibility and proximity to people or hospitals	LOT	SDG09	9.1
		SDG11	11.2
Performance of car transport network, ratio between accessibility and proximity to people or hospitals	LOT	SDG09	9.1
		SDG11	11.2
Gross Value Added (GVA) in Manufacture (ISIC rev4) as a percentage of GDP	PSS	SDG09	9.2
Manufacturing employment as a percentage of total employment	PSS	SDG09	9.2
CO2 emissions generated by the industrial sector	LTS	SDG09	9.2
Gini Coefficient	LOT, PSS, LTS	SDG10	10.1, 10.2
Share of social rental housing in the municipality	PSS	SDG11	11.1
Percentage of population satisfied with affordability of housing	PSS	SDG11	11.1
City inhabitants living in slums, informal settlements, or inadequate housing	PSS	SDG11	11.1
Public transport use for work commute (or to go to school)	PSS	SDG11	11.2
Transport energy consumption	LTS	SDG11	11.2
Ratio of land consumption to population growth rate	PSS	SDG11	11.3
Built-up areas per inhabitant	PSS	SDG11	11.3
Expenditure of local authority dedicated to the preservation, protection and conservation of cultural heritage per inhabitant	PSS	SDG11	11.4
Natural or Green Areas in the city/municipality	LOT, LTS	SDG11	11.4, 11.7
		SDG15	15.1, 15.2
Placement of artificial materials that cause the loss of essential soil ecosystem functions	LOT, LTS	SDG11	11.5
		SDG13	13.1
Areas exposed to flooding or urban flood risk	LOT, LTS	SDG11	11.5
		SDG13	13.1
Number of kg of residual waste compared to number of citizens (also number of kg selectively collected waste)	LOT, PSS, LTS	SDG11	11.6
		SDG12	12.5
CO2 equivalent emissions	LOT, LTS	SDG11	11.6
		SDG13	13.2, 13.3
PM10 concentrations	PSS	SDG11	11.6
NO2 concentrations	PSS	SDG11	11.6
O3 concentrations	PSS	SDG11	11.6
Number of kg selectively collected waste	LOT, LTS	SDG11	11.6
		SDG12	12.5
Green area/infrastructure (inside and outside the city)	LOT, LTS	SDG11	11.7
		SDG15	15.9
Share (%) of the total green area of the city/municipality	LOT, PSS, LTS	SDG11	11.7
		SDG15	15.2
The concept of ‘corridors’ or connected spaces for wildlife across the city is included in the action plans	LOT, LTS	SDG11	11.a
		SDG15	15.9
Connectivity measures in place	LOT	SDG11	11.a
		SDG15	15.9
Municipal waste processed according to differentiated reuse collection schemes	PSS, LTS	SDG12	12.5
Percentage of the city’s solid waste that is recycled	PSS, LTS	SDG12	12.5
Extent to which (i) global citizenship education and (ii) education for sustainable development are mainstreamed in (a) national education policies, (b) curricula, (c) teacher education, and (d) student assessment	LOT, LTS	SDG12	12.8
		SDG13	13.3
CO2 emissions per electricity production (tons of CO2 equivalent per gigawatt hours)	LOT, LTS	SDG13	13.1, 13.3
CO2 emissions per capita transport	LOT, LTS	SDG13	13.2, 13.3
CO2 emissions per capita	LOT, LTS	SDG13	13.2, 13.3
CO2 emissions per capita buildings and industry	LOT, LTS	SDG13	13.2, 13.3
Change in cooling degree-days needed to maintain an average building indoor temperature of 22 degrees Celsius	PSS, LTS	SDG13	13.2
Change in heating degree-days needed to maintain an average building indoor temperature of 15.5 degrees Celsius	PSS, LTS	SDG13	13.2
CO2 emissions from transport	PSS, LTS	SDG13	13.3
Protected marine areas	PSS, LTS	SDG14	14.5
Territory and diversity of habitats; forest area	LOT, LTS	SDG15	15.1, 15.2
Urban greenness, amount of green area in square metres as approximated by the Normalised Difference Vegetation Index (NDVI) based on satellite imagery.	LOT, LTS	SDG15	15.1, 15.2
Tree cover density	LOT, LTS	SDG15	15.1, 15.2
Total tree-covered surface area in the municipality	PSS, LTS	SDG15	15.2
Citizen satisfaction per municipal services identified	PSS	SDG16	16.6
Voter turnout	PSS	SDG16	16.7
Percentage of the eligible population that voted during the last municipal election	PSS	SDG16	16.7

LOT: linked to other target; PSS: proposed by several sources; LTS: linked to a SECAPs mitigation indicator; the indicators are listed by order or appearance considering the first target in which they are mentioned; the links between targets are based on the use of the same indicator to report more than one target.

.

5.4.2. Smaller Set of Potential Indicators

Out of the 114 indicators listed in the final set, 13 were particularly relevant due to their compliance with all filters, therefore allowing not only the optimisation of resources, reducing the number of indicators needed, but also enabling the benchmarking between cities and aligning long-term actions and goals in both the SECAP and SDG frameworks. As shown in

Table 2. List of potential indicators complying with all filters.

Indicator	Filter Complied	SDGs Goal	SDGs Related Target
Proportion of the electricity consumed in the city that comes from renewable sources	LOT, PSS, LT	SDG07	7.2
		SDG12	12.2
Population at risk of poverty, social exclusion, or after social transfers	LOT, PSS, LTS	SDG01	1.1, 1.2
		SDG10	10.2
Population living below the national poverty line	LOT, PSS, LTS	SDG01	1.4
		SDG10	10.2
Social/affordable homes delivered	LOT, PSS, LTS	SDG01	1.4
		SDG11	11.1
Housing cost overburden where the total housing costs represent more than 40% of the total disposable household income	LOT, PSS, LTS	SDG01	1.4
		SDG11	11.1
Ratio of the median free-market price of a dwelling unit and the median annual household income	LOT, PSS, LTS	SDG01	1.4
		SDG11	11.1
Number of deaths, missing, directly affected persons attributed to disasters	LOT, PSS, LTS	SDG01	1.5
		SDG11	11.5
		SDG13	13.1
Proportion of agricultural area under productive and sustainable or organic agriculture	LOT, PSS, LTS	SDG02	2.4
		SDG14	14.1
		SDG11	11.2
Effort rate of domestic users for the payment of water	LOT, PSS, LTS	SDG06	6.1, 6.2
		SDG15	15.1, 15.3
Unemployment rate	LOT, PSS, LTS	SDG08	8.3
		SDG10	10.2
Gini Coefficient	LOT, PSS, LTS	SDG10	10.1, 10.2
		SDG09	9.2
Number of kg of residual waste compared to number of citizens (also number of kg selectively collected waste)	LOT, PSS, LTS	SDG11	11.6
		SDG12	12.5
Share (%) of the total green area of the city/municipality	LOT, PSS, LTS	SDG11	11.7
		SDG15	15.2

LOT: linked to other target; PSS: proposed by several sources; LTS: linked to a SECAP mitigation indicator; the indicators are listed by order or appearance considering the first target in which they are mentioned; the links between targets are based on the use of the same indicator to report more than one target.

, 13 indicators complied with all imposed conditions, therefore showing their significance. This sample targets 11 of the 17 SDGs, with SDG01, No Poverty, and SDG11, Sustainable Cities, being the most represented ones.

A total of 25 different targets are tackled by the 13 indicators listed, hence representing 11% of the total official SDGs framework. As shown in the list, social aspects such as energy poverty are being closely monitored by cities and regions along with indicators related to quality of life, such as impacts from disasters, green spaces, and organic agriculture. Implementation of renewables seems to be also a common aspect that is being addressed by several local and regional authorities.

5.4.3. Top-Down vs. Bottom-Up Approach: Real-Case Implementation on the Harmonised Set of Indicators

Various methodologies and approaches can be employed to populate the set of indicators, leveraging publicly available data sources—from a top-down approach, which entails disaggregating data from the national or European level to a regional–local scope defining appropriated proxies such as population or square meters, or a bottom-up approach, which means filling in the indicators with existing local databases.

The possibility of approaching this from different directions is particularly relevant for smaller administrations, which often have limited access to data and resources. In that sense, a first preliminary analysis yielded that at least 75% of the indicators can be found in available open sources such as Eurostat, DG Region, or others, even though a more thorough analysis must be conducted to analyse the level of detail and the scope covered.

Likewise, as an example of the potential usefulness of the set of indicators proposed, this section describes the methodology followed by the LOCALISED project, which is a European-funded research project that aims to provide downscaled national decarbonisation trajectories and help upscale the definition and implementation of SECAPs and the monitoring of SDGs—in this particular case following a top-down approach. Nevertheless, it is worth noting that, as mentioned before, the usefulness of the set of indicators is not limited to a top-down approach and can be used as a starting point in bottom-up projects.

In this context and using a starting point, the set of indicators defined, two additional steps were introduced under this top-down approach, as shown in Figure 9. First, the list of indicators was filtered according to three different criteria: (i) the relevance of the indicator considering the aim of the project and the requirements of the different outcomes, (ii) the reliability and availability of data in open data sources at the scale needed, and (iii) the existence of a clear methodology to downscale the information to NUTS-3 regions if the data were not available at the desired level. During this process, only 6% of the total sample was discarded due to the lack of data and the impossibility of replacing the original source and 20% due to the scope of the project demonstrating the value of the set defined. As a final step, indicators that were adding different components, such as energy consumption from fossil fuels, were disaggregated into several single ones to allow a more detailed analysis of the current scenario, resulting in a final list of 250 indicators [160]. It is worth mentioning that not only was a substantial amount of data gathered, but also a precise disaggregation methodology was established to analyse the information effectively at the NUTS-3 level. This database of indicators can constitute a valuable resource for numerous European regions, especially for those which lack the resources or knowledge to begin planning.

5.5. Link between SDG and SECAP Plans

Concerning the last question, which addressed the link between the SDG and SECAP frameworks, the indicators related to both initiatives were listed to draw a clearer link between these plans and analyse the interconnection and potential synergies between the programmes. As mentioned above, 22 indicators out of the 114 indicators are linked to SECAP pillars. Figure 10 illustrates the SDG links within each pillar and the weight of the different goals. A clear connection between the SECAP mitigation pillar and SDG07, Clean Energy, SDG13, Climate Action, and SDG12, Responsible Consumption, can be spotted in the graphic as a strong connection between the adaptation pillar and SDG11, Sustainable Cities, SDG13, Climate Action, and SDG15, Life and Land, can be noted as well. Concerning the energy poverty pillar, the most recent assessment included in the SECAP comparable aspects are measured in SDG01, No Poverty, SDG10, Reduce Inequality, and SDG13 and SDG08, covering climate action and work and economic growth. Nevertheless, as represented in the graphic, there are many other relevant connections between the two plans, as each pillar is linked to eight different goals.

Moreover, as shown in Figure 11, half of the SDG goals can be linked to one specific pillar, whereas the other half is linked to more than one. SDG07, SDG13, and SDG11 are particularly relevant, first due to the amount of connection but also because they are linked to all three SECAP pillars in the first two cases and to two pillars in the second case. Additionally, potential aspects to be further developed in SECAPs can be identified by the lack of connections with SDG04, SDG16, and SDG17 or to the low number of connections with other relevant SDGs such as SDG05.

Furthermore, the analysis demonstrates that it is possible to address various aspects included in the SDG and SECAP plans with a limited number of indicators, reducing the complexity and effectively harnessing the limited resources that many regions and cities have. Several associations were recognised between targets and indicators, such as between SDG01, SDG07, SDG11, and SDG13, which have clear links to citizens and cities, energy, and climate change and to fundamental parts included in SECAPs as well.

Additionally, a Sankey graphic was constructed to illustrate the interconnections detected between the different goals and targets and the SECAP pillars, as shown in Figure 12. The thickness of the lines represents the number of indicators found in each target and the distribution considering the other targets where the same indicator is used. Since sometimes indicators were linked to only one target and to several in others, the inputs and outputs received by each target vary. As can be seen by the thickness of the connections, several common aspects were identified between SDG01 and the energy poverty pillar and between SDG07 and the mitigation pillar. Nonetheless, there are many other shared topics that both plans address. Considering that, in many cases, one single indicator is associated with multiple targets, there are more than 200 potential connections between the metrics proposed. Furthermore, all three pillars are linked to at least 20% of the total number of links established, demonstrating the vast interconnections that can be made between the two frameworks.

6. Discussion

Cities face many challenges related to sustainable development, such as limiting greenhouse gas emissions and improving living conditions. In that context, indicators can provide a solid basis for decision-making at all levels and measure the progress towards sustainable development at different scales. Even so, a plethora of indexes, indicators, and frameworks can be identified addressing the subject. In addition to the wide range of indicators and frameworks, up to this point, there has been no substantial effort to establish the interlinkages between the SECAP and SDG goals, even more so considering that indicators around mitigation have internationally recognised metrics.

The reference cases selected allowed comparisons between international guidelines, regional assessments, and specific frameworks developed by cities. Although it is worth mentioning that the sampling was mostly limited to initiatives within Europe, our analysis provides a comprehensive overview of the number of indicators included in initiatives launched in different parts of Europe and the priorities that current initiatives attribute to different aspects of the SDG goals.

From the analysis, several aspects can be highlighted.

First, since SDG and SECAP implementation is considered relevant for regional and local authorities, it is crucial to conduct further assessments to gain a deep understanding of their implications and the interactions between indicators and with other relevant instruments. SDGs and SECAPs are being used to align local plans but also as instruments to evaluate the actions done and the impact of the measures across different sectors. As can be seen in the literature, an increasing number of municipalities and regions are committing to adopting these plans, and an extensive number of papers and guidelines dealing with their implementation and analysing their synergies, challenges, barriers, and effectiveness can be found.

Second, cities and regions are relevant actors not only in the implementation of SDG11 but also in the successful achievement of many other goals. As shown in the analysis, SDGs have multiple interactions among themselves, and almost the entire set of indicators could be linked to actions planned under the umbrella of the CoM. Based on these findings, it will be essential to develop an integrated framework that offers clear guidance for all stakeholders involved. In particular, special attention should be paid to the common aspects addressed by both.

Third, despite numerous attempts to define the frameworks and indicators, as evidenced by the extensive literature available, there is no consensus on how to measure Sustainable Development Goals at the local level and on which indicators are most suitable to reflect local and regional realities. A clearer framework needs to be agreed upon among cities and regions to improve benchmarking and optimise the implementation of actions. As can be seen by the referred cases, there are several different approaches to selecting indicators. International and regional studies often choose a smaller sample of indicators to monitor and compare cities with a median of 37 indicators listed. In contrast, the median of indicators assessed for specific cities was 66.

Fourth, considering the limitations and barriers cited, it is necessary to find a balance between comparability and specificity when selecting appropriate metrics. As demonstrated, some sources prioritised the alignment with the international SDGs framework, therefore, comparability with other cities, while others created specific metrics considering the availability of the data and the region’s or city’s reality. The analysis showed that global indicators represented up to 33% of the total sets, while alternative indicators represented up to 68% of the total frameworks proposed in the studies. As an example, almost 56% of the indicators proposed by Barcelona were adapted to consider the specific reality of the city, whereas official global indicators represent only 6% of the total set.

Another relevant point to consider is the diversity of the variables chosen for monitoring a particular target; aspects such as the availability of data or disaggregated information at lower scales became relevant to choose appropriate metrics. Between 1 and 35 different proposals to monitor each target were listed, highlighting the huge number of possible metrics that could be selected. Some sources also underline the importance of contextualising indicators by comparing metrics with other relevant data, such as emissions with population or total energy production, instead of using absolute values.

7. Conclusions

The research described in this paper aimed to collect indicators from representative case studies, analyse the interlinkages between SDG targets and indicators and the metrics used in SECAPs, and propose a set of harmonised indicators for regional and local administrations. The research questions defined for the project pointed at (i) verifying which targets and indicators are being reported at the local level, (ii) identifying which metrics are most frequently used in lower scales, and (iii) highlighting potential indicators linked to more than one target, and that could serve both to monitor SDGs achievement and SECAPs implementation as well.

The results show that, in relation to the SDG targets assessed at the local scale, even though SDG11 specifically addresses cities, most of the local and regional frameworks have found connections with most of the SDGs, therefore stressing the necessity of analysing the SDGs as integral instruments with several aspects that cities and regions could track.

This initial analysis shows a strong connection between SECAPs and SDGs and the relevance of aligning the objectives of the two frameworks. Therefore, it is important to consider both plans at their initial states and carefully study their interactions to facilitate the achievement of goals and the monitoring of progress.

Additionally, thanks to this study, a list of potential indicators suitable for a large proportion of cities and regions was established. The analysis yielded a total of 114 potentially relevant indicators, 53% of those proposed by several sources, 57% linked to more than one target, and 20% of them associated with SECAP pillars. The list was composed by indicators that were either frequently included or linked to several targets, therefore emphasising the synergies between the different aspects and the targets and goals that integrated SECAP metrics. This outcome could facilitate better coherence among the initiatives, the optimisation of dedicated resources, and the alignment of long-term actions and monitoring processes. The set proposed could be used for guidance during the decision-making process and provide valuable insight into the aspects that other authorities are monitoring. The use of these indicators could allow comparability with other similar cities and regions and a critical analysis of the progress made over the years. However, given the varied contexts and range of indicators, a more in-depth analysis is necessary to establish priorities and enable optimisation. Various mathematical approaches, such as Pareto or sensitivity analysis, can be utilised to assess and determine the significance of the listed indicators and their importance within the set.

Lastly, the analysis of a short version of 13 indicators demonstrated that a small number of indicators can effectively cover various aspects of SDGs and SECAPs. This reduced set of indicators covers 25 different targets and several aspects related not only to energy but also to the quality of life. Therefore, it can be a good starting point to start the process, reducing the complexity of the task and allowing regions and cities to make the most of their limited resources.