Voluntary Planning and City Networks: A Systematic Bibliometric Review Addressing Current Issues for Sustainable and Climate-Responsive Planning

Abstract

Over the years, energy saving and climate change have sparked a challenge in developing innovative spatial and urban planning tools, methods, and approaches for urban areas and territorial management. This challenge has pointed out a gap in the traditional planning framework in tackling energy and climate issues, highlighting the need for renovated spatial planning practices. The current effective measures carried out by the complex network of stakeholders (public and private) are fragmented, and the role of city networks in shaping decisions and interventions has emerged. In particular, among the approaches for urban and territorial planning and the development of climate-responsive measures, this research adopts a specific focus on voluntary planning. The authors, through a literature review and an analysis of nine city networks, investigated how this approach addresses energy and climate issues and how it is linked to the city networks in designing investments and interventions within the urban context. From the authors’ perspective, city networks are the operative component in designing local experiences and applications, contributing to achievement of the global energy and climate targets according to the current policies. In this context, successful results with respect to climate and energy challenges is expressed in the degree of the awareness and the commitment achieved by the local communities. Moreover, reaching the climate and energy goals is a representation of the outcome of the interaction between the (public or private) actors involved and the degree of a city’s climate-responsiveness, rather than from a normative constraint or an institutional framework.

1. Introduction

“Cities are now acknowledged as a critical arena in which the governance of climate change is taking place” [1]. This statement summarizes, over the last decades, the significant role cities have taken in incorporating environmental considerations into their urban and territorial planning strategies towards sustainable development and low-carbon economy targets.

As highlighted by Hooghe et al. [2], local authorities have performed local climate change actions in climate protection within an explicit ‘multi-level policy framework’, distinguishing two types of multilevel governance: the first is characterized by jurisdictions at a limited number of levels, bundling together multiple functions, including a range of policy responsibilities, according to a system-wide architecture. The second is composed of specialized jurisdictions, and the governance is fragmented into functionally specific sections, providing a particular local service and solving a particular common resource problem without limits to the number of jurisdictional levels and leveraging a flexible design.

Energy saving and climate change have sparked a challenge in developing innovative spatial and urban planning tools, methods, and approaches for urban areas and territorial management. However, this challenge has pointed out a gap in the traditional planning framework in tackling energy and climate issues and a need for renovated spatial planning practices [3,4,5].

Specifically, climate action planning has become a top priority for cities to reduce greenhouse gas emissions and strengthen climate resilience, with improving mitigation and adaptation strategies in urban areas as key objectives for sustainable development [6].

There is a growing recognition that traditional top-down, government-driven, authoritative approaches are becoming less effective due to the shifting of responsibilities and resources across various political–administrative tiers spanning from the EU down to states, regions, and municipalities. Previous research [7,8,9,10,11] has observed that the top-down approaches, public-led actions are no longer politically and economically viable, whereas new methods based on public–private partnerships are being progressively adopted.

The trend of retreatment from the role of regulators on the part of the public authorities has fostered the involvement of private stakeholders in reaching planning goals [12], and public authorities became facilitators in designing new, preferably market-based approaches [13,14].

Consequently, the resulting approach to the climate and energy issues is fragmented when compared to the current effective measures carried out by the complex network of stakeholders (public and private). From the perspective of the authors, voluntary planning (VP) is a planning approach characterized by the engagement of the public and private actors/stakeholders, requiring an “urban and green” awareness in order to achieve successful results in terms of investment and interventions within the urban context.

The voluntary approach, through this perspective, can be considered as a tool able to improve the institutional framework in pursuing the sustainability, efficiency, and engagement issues and making the institutional processes of local governance more flexible. However, this approach supported the development of several interventions on urban areas that were “missing an urban vision” [15] and were operated by non-integrated sectors (i.e., residential buildings, transport, energy, etc…). In any case, the voluntary approach should be evaluated as an opportunity for small cities to develop a sustainable and climate proof policy; but at the same time, the need arises to design an assessment framework that is able to monitor and evaluate the development of actions and policies undertaken. In order to build a comprehensive vision for VP through a conceptual paradigm, the role of city networks in shaping decisions and interventions emerges.

Acuto and Rayner [16] define city networks as “formalized organizations with cities as their main members and characterized by reciprocal and established patterns of communication, policy-making and exchange”.

In detail, from the authors’ perspective, city networks are the operative component in designing local experiences and applications for contributing to the achievement of the global energy and climate targets according to the current policies.

The aims of the research are the following: (1) investigate the pathway of the VP approach in planning energy and climate adaptation policy implementation, and (2) investigate the role played by the city networks on such subjects.

In order to achieve aims (1) and (2), a literature review on VP and an assessment on a set of nine city networks were performed (details of the selected city networks are given in the Supplementary Material).

The research is structured as follows: Section 2 shows the methodological approach adopted and Section 3 provides the relevant results and discussions achieved via the research, while Section 4 presents the conclusions and future perspectives of this research.

2. Methodological Approach

The research is structured in two parts: the first part examines the path of the VP approach in planning, while the second part focuses on the role played by city networks in such issues. The path of the VP approach was examined through a bibliometric analysis in order to understand whether this approach is “recent” or consolidated over the years according to the methods described in Section 2.1. Following this, the role played by city networks was investigated according to the analytical steps illustrated in Section 2.2.

2.1. Literature Review on Voluntary Planning

There is not a clear date, event, or agreement able to identify the beginning of VP related to urban and territorial development; despite that, it is possible to identify the training path that has supported the establishment of VP related to urban, territorial, and environmental issues.

In order to identify this training path, the authors performed a review on the Scopus website (accessed on 12 September 2023) of the words “voluntary planning” as portrayed in Figure 1.

The search was carried out using the query (voluntary AND planning) by title, abstract, and keywords and 8053 documents were retrieved.

Focusing on the planning issues, the bibliometric analysis was refined by limiting the subject areas (i.e., excluding medicine, chemistry, and biological subject areas) and including only published articles in the English language. The final query (TITLE-ABS-KEY (voluntary AND planning) AND (LIMIT-TO (SRCTYPE, “j”)) AND (LIMIT-TO (SUBJAREA, “ENVI”) OR LIMIT-TO (SUBJAREA, “ENGI”) OR LIMIT-TO (SUBJAREA, “SOCI”) OR LIMIT-TO (SUBJAREA, “EART”) OR LIMIT-TO (SUBJAREA, “AGRI”) OR LIMIT-TO (SUBJAREA, “ENER”)) AND (LIMIT-TO (DOCTYPE, “ar”)) AND (LIMIT-TO (LANGUAGE, “English”))) submitted to Scopus retrieved over 1000 documents.

Data analysis and data visualization were performed through the open-source software Bibliometrix 4.3.0 [17,18].

2.2. Assessment of Selected City Networks

The authors provided an overview of a limited group of city networks operating inside and outside the European borders. These city networks were selected because they focus on climate-responsive processes, adopt a voluntary approach, and are closely linked to each other.

The selected city networks are the following: the United Cities and Local Government (UCLG), Eurocities, the Climate Alliance, ICLEI, Energy Cities, METREX, C40 CITIES, CIVITAS, and the Global Covenant of Mayors for Energy and Climate.

The authors opted for six features to support the description of the city networks selected: establishment, city population size, number of signatories, targets, network of networks, and membership fee rules. The first three are features that provide facts about the operational years of these city networks, the population size that they are referred to, and their extension and relevance in terms of signatories. “Targets” explains the main activities and energy, climate, environmental, or social issues tackled by each city network.

Network of networks is a feature defined by the authors in order to provide an overview on the connections among city networks operating at the EU and international level. Moreover, this feature, besides highlighting the city network that is more connected to the others, allows for the identification of the city networks that share common targets. The last feature, membership fee rules, is the cost of membership and its rules. It was selected because of the fee payment that could be considered a barrier for some municipalities in the choice of a city network membership. Even if there are open-access city networks, the membership fee represents a feature taken into account by municipalities during the selection of a specific city network instead of another.

3. Results

3.1. Results from Bibliometric Analysis

Results from the bibliometric analysis reported 1208 publications covering a timespan of over 80 years, and Figure 2 shows a comprehensive dashboard of the main information retrieved from the dataset built by the authors.

Regarding the publication of articles (Figure 3), there is a general increasing growth trend over the years, and it is relevant to highlight that after the year 2000, the frequency of published articles is always above 20 per year on average (except for a slight decrease in 2002). The increasing trend in scientific production could be linked to the development of energy and climate policies at the national and international level, as well as the growing awareness and interest in voluntary planning.

Regarding the scientific production of the countries (Figure 4), the United States of America is the first one, followed by the United Kingdom and Australia. The common Anglo-Saxon roots of these three countries provide an insight into planning approaches tackled in these countries. It can be seen that the voluntary approach has been of particular interest in these countries, in comparison to others [19,20].

In order to understand the themes that drive (and have driven) the trend of the VP approach, the authors developed a thematic map derived from the co-word analysis. The co-word analysis indicates the conceptual structure and highlights the link between concepts through term co-occurrences.

A thematic map is a two-dimensional diagram where density and centrality are used in classifying themes [21,22]. Themes are classified in four quadrants: (1) upper-right quadrant: motor-themes; (2) lower-right quadrant: basic themes; (3) lower-left quadrant: emerging or disappearing themes; (4) upper-left quadrant: very specialized/niche themes.

Authors’ keywords were selected as a field of investigation in developing the thematic map.

The results shown in Figure 5 indicate a link between VP and climate change and sustainable development issues. They represent fundamental issues and are a necessary background to comprehend the VP processes. Another relevant feature relates the VP to the themes of ecosystem services and spatial planning, which are on the borderline between niche and emerging (or declining) themes.

The basics themes in the thematic map reiterate the relation between “traditional” and “incoming” issues in describing voluntary planning. Traditional issues are governance, planning, and regional planning, whereas incoming issues are climate change and sustainable development. Thus, investigating these last two themes allows for a better understanding the pathway of the VP approach over the years.

In order to understand how the keywords related to VP over the years, a thematic evolution of the authors’ keywords was performed, as shown in Figure 6. The year 2015 was chosen as the middle year, because it was the year in which the Paris Agreement was adopted. Before the year 2000, VP was described by three keywords without a direct link to energy or climate issues. The middle time slice (2001–2015) registered a set of 20 keywords describing voluntary planning, including specific reference to climate change and its risks such as droughts, climate policy, and risk assessment. Furthermore, through keywords selected by the authors, the voluntary aspect of planning processes emerged, including participatory planning, voluntary environmental processes, or the voluntary sector.

Considering the last decade, (2016–2023) VP was clearly described by keywords including climate change and voluntary issues. In detail, the keyword “Planning” showed the shift in the research towards the current issues such as climate change, green infrastructures, and collaboration in planning processes. Moreover, in the middle slice, for the first time, the keyword “participatory planning” appeared that was explained better in the last decade through the keywords “indicators” and “public participation”. This last remark provides for an insight on the approaches to voluntary planning, based on the issues of climate and the participatory planning of the processes. Another interesting aspect of VP that emerged in the last decade is the indicator-based approach that characterizes the current mainstream research.

Analyzing the results achieved via the bibliometric analysis, a possible training path for the VP emerges. According to the scientific production, VP is more rooted in the Anglo-Saxon countries than others, and the basic themes in Figure 5, such as “planning, climate change, sustainable development, governance, and regional planning” show that VP entirely falls within urban, territorial, and environmental issues. Moreover, VP is also linked to “traditional” themes such as spatial planning as well as emerging themes such as ecosystem services. Figure 6 portrays this pathway, highlighting specific references to climate change, green infrastructures, and collaboration in planning processes through VP keywords.

3.2. City Networks: An Overview

The findings presented in Section 3.1 have suggested a preliminary framework for delineating the VP approach in the context of energy and climate adaptation policy implementation. This following section addresses the role of city networks in relation to these matters.

Over the years, cities have committed targets to solve common issues (such as environment, mobility, disaster risk reduction, climate change, social, and economic issues) that afflict them, designing widespread interventions able to be improved and replicated in similar territorial contexts. An example of this “imitation game” can be found at the Copenhagen Climate Summit in 2015, where the mayors involved in the summit on climate change were impressed by the fact that, despite snow and darkness, one out of three Danes commuted to work on a bicycle in dedicated bike lanes. Seeing this phenomenon, many mayors looked for ways to get more of their constituents out of the car and onto a bike, and mayors from Rio de Janeiro and São Paulo realized that bikes could not only reduce pollution but also enable people who were too poor to afford public transit to commute to jobs [23].

Other examples in understanding that common issues such as environment and pollution were not only the problems of each country but went beyond national borders can be found in a number of events that have been raising EU environmental awareness: “acid rain” in the 1980s caused by UK coal-fired power stations damaged forests and lakes in Scandinavia [24,25,26]; pollution caused by discharges into the Rhine, the Meuse, or the Danube rivers in another country further downstream [27,28,29].

However, the experiences gained by each local authority cannot be kept alone but should be shared with other local authorities, hence the establishment of the city networks as “hubs” where successful experiences are shared so as to provide support to reach similar results in the same contexts.

City networks gather their members on a specific feature (population size, geographical location, economic conditions, …) or because of achieving an objective (sustainable development goals, energy efficiency, climate change adaptation/mitigation, …). Considering the first group, city networks can provide a relevant support to small local authorities (i.e., below 5000 resident inhabitants) because they are representative of a larger territorial extension than metropolitan areas, notwithstanding their contribution in terms of CO₂ emission reduction and climate responsive interventions which is small compared to the worldwide volume.

Considering the second group, city networks could play an important role in defining and developing climate policy at a city level [30], such as the role played by the ICLEI, C40, or Covenant of Mayors members. These aspects have emphasized those territorial contexts where there is not a specific climate commitment at a local level or there is a lack in technical skills able to adopt policies independently and proactively.

In

Table 1. The dashboard of selected city networks.

City Network	Establishment	City Population Size	No. Signatories (as at 2023)	Targets	Network of Networks	Membership Fee Rules
United Cities and Local Government (UCLG)	1913	All population sizes	Over 240,000 towns, cities, regions, and metropolises and over 175 associations of local and regional governments	Representing interests of local and regional governments worldwide. Advocating for the localization of SDGs and promoting the role of local governments in addressing global challenges such as climate change, urbanization, and sustainable development.	Association of Netherlands Municipalities, C40 Cities Climate Leadership Group, Global Covenant of Mayors, ICLEI	Membership fees are based on a calculation that takes into account the number of inhabitants represented by the member and the state of the country’s economic development.
Eurocities	1986	Over 250,000 Inhabitants	208	Eurocities represents the voice of cities at the EU level to bring about change on the ground. It shares and facilitates the exchange of knowledge, experience, and good practices between cities to scale up urban solutions.	TheMayor.EU—the European Portal for Cities and Citizens, CIVITAS, UCLG	Both full and associate members of the Association will be required to pay an annual subscription fee. A city who has not paid its subscription fee will automatically drop out of the members list. The amount of this fee will be proposed by the Executive Committee and formally approved by the Annual General meeting.
Climate Alliance	1991	All population sizes	1969	Reduction in CO2 emissions by ten percent every five years (equivalent to a half of per capita emissions by 2030 as compared to 1990); reduction in emissions to 2.5 tons of CO2 equivalents per person via energy saving, energy efficiency, and the use of renewable energy, promoting climate justice in partnership with indigenous peoples by supporting their initiatives, raising awareness, and abstaining from the use of unsustainably managed tropical timber.	Global Covenant of Mayors for Climate and Energy, European Committee of the Regions	Fees are moderate and structured so that they are feasible even for the most economically strained municipalities. Local authorities pay just EUR 0.0077 per resident per year. Annual fees are capped at a maximum of EUR 15,000 and a minimum of EUR 231 per member, municipality, or district. Indigenous people’s organizations are under no obligation to pay fees. The Executive Board decides on annual fees for associated members on a case-by-case basis.
ICLEI	1990	All population sizes	1075 members (including more than 2500 local and regional worldwide governments)	Working alongside local and regional governments to anticipate and respond to complex challenges, from urbanization and climate change to ecosystem degradation and inequity. At national and global scales, pushing for robust policies that reflect the interests of local and regional governments and applying global policies to sustainable urban development strategies at subnational levels.	Global Covenant of Mayors for Climate and Energy, C40, UCLG	ICLEI members pay an annual fee based on the number of inhabitants in the local and national area based on per capita income. According to four groups classified per Gross National Income Per Capita (local Governments from EUR 100 to 8000)
ENERGY CITIES	1990	Municipalities, inter-municipal bodies and consortia, local energy agencies, and municipal companies chaired by an elected member specialized in regional or national associations of municipalities working in the same sector as that of Energy Cities/Energie-Cités. Municipalities located outside geographical Europe may have the status of Associate members	180 member cities	Sharing of knowhow in the fields of energy management, development of renewable energy sources, and reduction in pollutant and greenhouse gas emissions, to contribute to strengthening the role and capabilities of municipalities and local authorities in the areas of energy consumption, distribution, and production and more generally local energy planning.	Global Covenant of Mayors for Climate and Energy, METREX	Annual fees are adapted to the specific context of the members. It depends on the number of inhabitants.
METREX	1996	Metropolitan areas	120 metropolitan regions and areas	Strategic planning and development at the metropolitan level.	EUROCITIES	The cost of the fee is related to the membership type
C40 CITIES	2005	Megacities	96 member cities	Adoption by the cities of a resilient and inclusive climate action plan aligned with the 1.5 °C ambition of the Paris Agreement and regular updates. In 2024, the city remains on track to deliver its climate action plan, contributing to increased resilience, equitable outcome, and halving C40’s overall emissions by 2030.	Global Covenant of Mayors for Climate and Energy, ICLEI, UCLG	C40 member cities earn their membership through action. C40’s most distinguishing feature is that it operates on performance-based requirements, not membership fees.
CIVITAS	2002	All population sizes	Over 340 local authorities	Promotion and implementation of sustainable, clean, and (energy) efficient urban transport experiments. Demonstration of integrated packages of technology and policy actions in the field of energy and transport in eight categories of measures. Built up critical mass and markets for innovation by transferring good practices to other European cities.	Global Covenant of Mayors for climate and energy, Eurocities	Membership is free and open to all who sign the CIVITAS City Declaration.
COVENANT OF MAYORS FOR ENERGY AND CLIMATE	2008	All population sizes	11,820 EU27 signatories	Achieving climate neutrality by 2050 according to the EU objectives, with the commitment to mid- and long-term targets. Developing a climate pact with all players (i.e., citizens, businesses, and governments at all levels) engaged in the processes. Networking with fellow mayors and local leaders, in Europe and beyond.	ANCI, CIVITAS, C40, Climate Alliance, Energy Cities, ICLEI, UCLG	The GCoM is based on a voluntary commitment. Joining the GCoM is fully free of charge.

, the authors provided an overview on a limited group of city networks operating inside and outside the European borders listed per year of establishment and classified by the six features.

The overview on the city networks shown in Table 1, through a dashboard of six features, carried out a first assessment on connections between policy objectives and city networks operating within the voluntary planning domain.

Establishment allows for the identification of the “oldest” city network among the nine selected. Meanwhile, it shows which city network has gathered the highest number of signatories compared to the founding period.

City population size indicates the population size to which they are related. It is important to note that six out of nine city networks include municipalities of all population sizes, while only three of them are referred to a specific population size (metropolitan areas or megacities).

The number of signatories lists the members of each city network and provides an indication of the size of the city network in terms of number of members. A comparison between this feature and the establishment feature reveals that the “oldest” UCLG has gathered the highest number of signatories, but the “youngest” Global Covenant of Mayors for Climate and Energy has increased by over 10,000 signatories in less than 20 years.

Targets offers a summary of the visions, objectives, and commitments of each city network. Within the targets are included both references to the energy and climate policies (such as the Paris Agreement or EU climate policies) and the contribution to the municipalities in supporting their development and capabilities towards the clean energy transition.

“Network of networks” (Figure 7) allowed for a better explanation of the connections among the city networks highlighting the more “social” city network and the connections due to common or shared targets. Specifically, the more “social” city network is the Global Covenant of Mayors for Climate and Energy, which is linked to six (out of nine) city networks, compared to an average of two links for the other city networks.

Membership fee rules show (list) the economic requirements asked for the signatories of each city network. Among them, only two out of nine are free and open to all population size municipalities. The majority of city networks (six out of nine) require a membership fee depending on the number of inhabitants and membership type. C40 is the only one featured by the functioning on performance-based requirements, not membership fees.

Among the specific features of the city networks assessed in this research, there emerged some significant highlights.

UCLG, as a global network of cities and local, regional, and metropolitan governments and their associations, is committed to representing interests of local and regional governments worldwide. It serves as a platform for collaboration and cooperation among municipalities, cities, and regions from different countries in addressing global challenges such as climate change, urbanization, and sustainable development. UCLG strengthens its network by enhancing political participation, designing new tools for synchronized action and renewing partnerships with different actors.

Eurocities is one of the EU city networks with a specific threshold in terms of population-size. Metropolitan areas larger than 250,000 inhabitants are eligible signatories, and the targets are related to population size. Eurocities represents a city network strongly involved in social issues and provides equal opportunities in promoting diversity, recognizing cities as policy makers, service providers, employers, and buyers of goods and services. Actually, among the targets, there is the promotion of measures that contrast the urban sprawl towards the models of compact, integrated, and organic cities and during the last years, with the Integrating Cities Charter, they have set commitments on the integration of migrants, providing an overarching framework for work in this area.

With this perspective, the Climate Alliance is the first city network tackling the climate issues with a specific focus on the local level. It emphasizes the role of the municipal involvement in climate protection and considers cities and towns as key element in the implementation of the 2030 Agenda with its Sustainable Development Goals. The introduction of the Climate Alliance Charter boosted the voluntary commitment of the signatories in their local climate strategies, oriented towards a “continuous reduction of greenhouse gas emissions”.

ICLEI works like a city network, providing technical consulting to local governments to meet environmental and sustainability issues, despite the fact that it is technically an international non-governmental organization. The self-defined commitment to climate protection represents the only requirement for membership, and there is not a limitation in terms of population size. This allows for the engagement from local to global levels, shaping policies and sparking actions to transform urban environments worldwide.

METREX is a city network designed specifically for the metropolitan regions and areas. Its fundamental aims are related to integrating strategies for sustainable development, metropolitan land use and transportation, urban growth, renewal and regeneration, and strategies for environmental renewal.

METREX works to enhance funding, budgets, and the position of its signatories on the European and/or global level, which often translates to better outcomes for citizens, businesses and institutions. It contributes the metropolitan dimension to policies, programs, and projects on a European scale. It plays an active role in starting and coordinating metropolitan developments, considering that many of the METREX challenges can be tackled in coordination with other metropolitan areas in Europe.

ENERGY CITIES is a city network that includes local and regional authorities but also municipal agencies or companies, as well as regional authorities and their subordinated organizations, willing to engage in the energy transition. A key feature of ENERGY CITIES is the internal organization governed by the principles of holacracy, which means decisions are made by the person or “circle” responsible for a role. Ambition and commitment to share experiences are required by the signatories in order to reach climate neutrality in the territories by 2050 and to align the local strategic development with the Paris Agreement.

C40 Cities is a city network exclusively related to megacities aimed at the cooperative reduction in climate pollution. C40 member cities have developed broad efforts to build climate action through peer-to-peer knowledge sharing, including climate action planning, buildings, transport, energy, and adaptation.

CIVITAS, as well as ICLEI, acts as a network of cities, for cities, with a specific focus on sustainable urban mobility. It supports the European Commission in achieving its ambitious mobility and transport goals, according to the European Green Deal. CIVITAS fosters political commitment and boosts collective expertise, supporting the development of policies related to the mobility towards decarbonization processes. The current phase of CIVITAS 2030 (2021–2025) supports cities to make smart and sustainable urban mobility systems and ensures that mobility is a driving force behind the building of climate-neutral and resilient cities.

The Global Covenant of Mayors (G-CoM) initiative was launched in Europe fostering the ambition to gather local governments voluntarily committed to achieve and exceed the EU climate and energy targets. The approach pursued by G-CoM signatories is bottom-up and currently G-CoM counts over 10,000 signatories thereby becoming the largest global alliance for city climate leadership. It is relevant to highlight that among the G-CoM signatories, 63% of them have a population below 10,000 inhabitants. The G-CoM is the only city network analyzed in which each signatory develops a plan: the Sustainable Energy and Climate Action Plan (SECAP). Through the SECAP, commitments and policies towards climate neutrality have been put into practice through a standard set of sectors on environmental, social, and urban issues. SECAPs represent tools that are useful to drive the territorial governance under the perspective of “the green responsibility”, helping the local administrators to manage the urban and territorial transformation processes towards a low-carbon economy and European climate-proof cities. Furthermore, SECAPs could fill the lack of Local Climate Plans among European cities where skills and resources of local governments are missing [31]. From this perspective, G-CoM experiences among the European cities have highlighted the planning role of the SECAP that produced a new perspective in rebuilding cities and shaping territories, contributing to improving the quality of life and the city welfare according to SDGs.

4. Discussion

4.1. Evidence from the Bibliometric Analysis

The VP approach represents a field of research tackled in a scientific article for the first time in 1936, ref. [19], where it is affirmed that “voluntary organization is a peculiarly American institution” and it is not without its counterpart abroad. In the same article, the need for a well-established procedure and operating technique is highlighted before being incorporated into a government framework. Moreover, the need of a structured framework is pointed out by the fact that both the official planning commission and the VP association are necessary, because each one is fitted to perform certain functions which the other is either not able to perform as well or cannot perform at all [32].

Aiming at finding a specific time start, Beaufoy locates the growth of modern civic consciousness from 1890 to 1920, when citizens began to exercise their right to participate in the planning and design of the urban environment. Research claims that civic consciousness, in that period, shifted from a nineteenth century philanthropic approach to urban reform, advocating a more professional and democratic attempt to attend to the planning of the entire urban environment by focusing on the relationship between the town planning movement, the local government, and a VP and amenity group, the London Society, founded in 1912 [33].

The first geographical (in other words: place-based) approach of VP came back in 1981. In the paper “A small area profile system: its use in primary care resource development” [34], VP was a means to collect and evaluate secondary source data as site testing for the development of rural primary care clinics in order to have a small demographic area with primary care resource profiles. Still, in 1981, a second paper in medical geography, “VP forestalls excessive competition, regulation” [35], evaluates VP as an aid for institutions to achieve cost containment without undermining long-range goals.

Only in 1983, Errington and Thomas [36] related VP to environmental issues, providing a brief account of a project designed to sensitize people of all ages to the environmental problems and opportunities in their community, within the scenario of modifications in South Wales with the redevelopment of the Cardiff city center, the slum clearance improvement program for older housing, and the scrapping of the Buchanan Plan. Always in England, VP operating with aid groups was the reaction to the reduction in time and resources allocated to the public consultation and participation from the environmental professions against the outlook of that period; “less planning is better planning” [37].

The 1980’s and 1990’s saw the onset of a period characterized by the establishment of programs (i.e., Water Agency Response Network) and city networks (i.e., Eurocities, Climate Alliance, ICLEI, etc.) that operated on a voluntary approach of their members and improved the overall response capabilities of agencies that were experiencing significant damage to their systems through VP [38].

The increasing awareness of environmental issues on greenhouse gas (GHG) emissions and climate change, with the institution in 1988 of the International Panel on Climate Change [39] and “Acknowledging that change in the Earth’s climate and its adverse effects are a common concern of humankind” from the United Nations Framework Convention On Climate Change [40], added VP to the environmental key components for tackling climate change through a responsive climate planning.

Indeed, since the 1990’s, VP has emerged in voluntary programs, suitable to address specific urban governance issues and providing a means for taking action in situations in which it is too costly or difficult to implement direct regulatory interventions [41]. Voluntary programs have become conventional instruments in urban climate governance [42,43]; however, city governments should consider that urban or territorial problems can be addressed with voluntary programs if they are legitimated by the actors and stakeholders engaged therein [44,45].

In this context, there emerged the role of City Networks (and initiatives promoted by private foundations) in designing climate and energy efforts and interventions with a voluntary approach for achieving sustainable development objectives and energy/climate targets.

This voluntary approach has characterized the last two decades, becoming a distinctive label of such city networks as the Global Covenant of Mayors for Climate and Energy and has overcome the institutional processes of urban planning.

The initiative developed effective practices, useful technical contributions in selecting intervention priorities, and the design of feasible project frameworks for public and private investments [46]. On this track, VP has supported actions related to the targets set by the European Community or International Agreements, supporting the urban development processes. Furthermore, it has highlighted the unsuitability of the current normative framework concerning urban development and management to express required performances in promoting actions and tools (the ‘plans’) oriented towards applying sustainable development principles and climate adaptation/mitigation [15].

4.2. Evidence from the City Networks Overview

City networks have supported climate action planning. It became a top priority for cities to reduce greenhouse gas emissions and strengthen climate resilience, while improving mitigation and adaptation strategies in urban areas as a key objective for sustainable development. Moreover, city networks can be intended as the operative component in designing local experiences and applications scaling the global energy and climate targets according to the current policies. In this perspective, cities considered as ‘delivery agents’ of EU policies, as provided by the Energy Cities impact report 2022, report the current operative connection between policies and city networks. We may refer to this role as a peculiar “skill” of the cities engaged in such policies; it derives from scaling down global solutions to local experience. It is demonstrated that such targets can only be achieved if they are integrated into planning, policy-making, and action [47]. However, the approach to the climate and energy issues under the umbrella of VP is fragmented if compared to the current effective measures implemented by the complex network of stakeholders (public and private) [48].

The VP approach has designed an “additional” approach, and it is irrespective of the institutional processes. It can be considered as a variable aspect because it is related to the environmental awareness and engagement of the citizens in the urban issues that are not pursued likewise worldwide.

This approach enabled working groups to tackle energy efficiency, climate change, and social issues, and additionally, it has become mainstream to communicate and share experiences suitable for all (as examples, Car Free-Day or World Environmental Day). It is a mark of the commitment level of the local authorities that often supports and promotes the establishment of local groups of municipalities in reducing energy, sharing common targets, and supporting innovative processes.

Furthermore, the voluntary approach overcomes stiff institutional processes, sharing common targets but achieving them with more flexible processes. Related to this, are those experiences developed in Denmark integrating climate change into institutional processes [49] or those widely adopted in Europe within the Covenant of Mayors initiative [50,51], as well as detailed for Italy, where the voluntary approach has unlocked the planning processes in urban areas [46]. Another relevant issue is to consider how the engagement of the stakeholders and citizens involved in the processes plays a fundamental role in achieving successful results in those contexts where there is a complete normative national framework as opposed to a fragmented local one.

From the perspective of the authors, VP is a planning approach characterized by the engagement of the public and private actors/stakeholders, requiring an “urban and green” awareness in order to achieve successful results in terms of investments and interventions within the urban context. From this perspective, the role of city networks emerges in shaping decisions and interventions that allow for a comprehensive vision for the VP through a conceptual paradigm. Moreover, the challenge of energy saving and climate change requires innovative tools in spatial and urban planning, and at the same time, there is a gap in the traditional planning framework for tackling energy and climate issues and the need for renovated spatial planning practices arises [3,4,5].

In addition to the VP approach, from the city’s perspective, the opportunity to be part of a community provides local authorities with opportunities in terms of policy development, technical support, and enhancing their global relevance.

This membership aspect has increased the adoption of (environmental and non-environmental) policies, especially if cities have interests in public health and economic development co-benefits [52], as well as co-benefits deriving from the reduction inf air pollution and fossil fuel consumption (as a result of energy efficiency policies) [53]. Furthermore, it is a significant opportunity for the small cities (i.e., below 5000 resident inhabitants), where there is usually the a of technical skills, to unlock the development of policies or launch them without additional support, as opposed to the Metropolis or large cities (i.e., with a number of resident inhabitants over 50,000) where technical teams are skilled in developing policies and planning interventions. Small cities, through the support of the city networks, have expressed their contribution to achieve global climate and energy targets and have increased their worldwide significance to be active players just like the larger cities.

On this track, city networks have supported and reduced the gap between large and small cities in developing environmental and non-environmental policies, operating outside institutional processes and fostering the achievement of sustainable development goals and facing climate change.

Lastly, the participation in a city network is an opportunity for cities and local communities to achieve common goals with well-structured support, learning from each other and sharing good practices [54]. In this context, the city network deriving from the 100RC Initiative can be considered a remarkable example of how “knowledge co-production amongst cities and city-networks could bring about new urban solutions applicable across scales and across geographies for urban resilience and urban sustainability”, as remarked by Elmqvist et al. [55].

Membership fees could represent a barrier to membership, especially for the small cities, due to their limited financial resources. The G-CoM and Civitas can be an opportunity to promote participation in a city network and retrieve the benefits in terms of knowledge sharing and capacity building in a free-fee membership. At the same time, if ICLEI, Climate Alliance, and UCLG take into account membership fee rules, they are linked to the G-CoM. Thus, the members of these city networks still have the opportunity to be indirectly in contact.

5. Conclusions

The research has identified the VP approach as an expression of the awareness and commitment gained by the municipalities. This approach can promote bottom-up processes that allow the local community and local players to express their views and needs for the local sustainable development in line with the SDGs.

This research highlighted some non-formalized urban planning practices that are essential in addressing urgent sustainability issues. This is even more important in contexts (for example the Italian one) where the planning regulatory framework is not up to date, and consequently not able to tackle the current challenges related to climate change [56,57].

The framework of VP also introduces a new urban planning paradigm: energy efficiency and climate challenges require a new generation of planning tools, and SECAP (suggested by the G-CoM) is such a candidate for the production of relevant changes to the complex system of EU municipalities integrating specific urban issues and the wider territorial sustainable objectives [15]. In this perspective, the SECAP approach, intended as a tool to facilitate decision-making processes in energy and climate local actions, is very flexible if compared to other institutional planning processes and could fill the gap of traditional urban planning tools concerning the objectives of GHG reduction and climate adaptation/mitigation [58]. These plans can be considered as indications of the planning platform of European cities, thereby making the European cities approach in managing climate adaptation and energy sustainable transition comparable across the EU as it is based on a common planning approach, a common planning scheme, and common evaluation metrics.

A holistic approach, as suggested by G-CoM, ICLEI, C40, or 100 Resilient Cities, could be the solution to design and compare similar experiences among the municipalities towards building an effective adaptation/mitigation strategy facing the climate-change challenges for future sustainable cities included in the low-carbon transition process.

The holistic approach, together with the bottom-up approach, could represent a suitable mix for VP in achieving the following goals:

• Better orienting the decisions and initiatives taken on by the municipalities;
• Better evaluating the interventions conducted, improving the interventions in accordance with the local needs towards sustainable development;
• Better defining the contribution to the climate and energy challenge of the “small” to the “major” municipalities.

The role of city networks in designing and shaping interventions coupled to VP can underpin those weak municipalities, where awareness and commitment are effective but are opposed by technical and financial barriers. This is the case of the small municipalities (i.e., below 10,000) that are strongly aimed at joining the effort to combat the energy and climate challenge but encounter several barriers (technological, financial, or logistic) as opposed to bigger municipalities. Moreover, the meeting of the foundations with the city network could be an opportunity to improve the local development with ad hoc investments and enhance engagement processes of public and private actors involved in planning processes. We can confirm that this produces a higher awareness in local communities towards planning as a process to address local needs in a strategic and integrated long-term view.

A relevant component to be included in a further development of this research is the involvement of citizens [59] and the engagement of stakeholders in the SECAP design process. This is a grey area, and it requires effective participation methods [60,61,62,63] (such as public consultation, working groups, forums, and workshops) in order to produce improvements to the plan without affecting the effectiveness of the process.