Green Infrastructure and Adaptation to Climate Change in Marginal Areas: A Reference Scheme for Implementation Guidelines in Italy

Abstract

Marginal areas (MAs) can show scarce disaster resilience in the context of climate change. Proactive adaptation to climate change (ACC) based on green infrastructure (GI) has the potential to increase the disaster resilience of the MAs. The scientific literature has scarcely addressed research on methods and guidelines for promoting ACC and GI to increase the resilience of MAs. No previous research has focused on a method to set a reference scheme for implementation guidelines concerning the use of GI as an ACC approach to deal with the effects of a changing climate in Italian MAs. In this regard, this study aims to provide planners and public administrations with an appropriate scheme to foster the mainstreaming of ACC and GI into the planning of MAs. To do so, we proposed and applied a methodological approach consisting of the scrutiny of the scientific and grey literature with the purpose of distilling a set of key elements (KEs) that need to be considered as a reference scheme for implementation guidelines. As main findings, we identified ten KEs relevant to drafting guidelines for integrating ACC and GI into planning tools, e.g., a clear definition of GI, participative approaches, public–private cooperation, and others, that will be tested in ongoing research.

1. Introduction

Marginal areas (MAs) can be defined as contexts rich in natural resources, characterized by a lack of infrastructure, significantly far away from essential services, and suffering from sociodemographic and economic difficulties, such as depopulation, unemployment, and low income [1]. In Italy, these areas cover approximately 60% of the entire national territory and host a quarter of the population [2]. In MAs, extreme weather events occurring in the proven context of climate change can exacerbate negative effects, such as floods, landslides, droughts, heat islands, etc., which are becoming increasingly intense and frequent [3,4,5].

According to the IPCC [6], climate change can be defined as “a change in the state of the climate that can be identified […] by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer” and adaptation as “[in] human systems, the process of adjustment to actual or expected climate and its effects, in order to moderate harm or exploit beneficial opportunities. In natural systems, the process of adjustment to actual climate and its effects; human intervention may facilitate adjustment to expected climate and its effects” [6]. The Mediterranean region is one of the “hot spots” of climate changes, with warming exceeding by 20% the global average increase, and a reduction in rainfall [7]. In Italy, statistics point out that the average temperature is increasing, and there is a general increase in the intensity of rainfall events [7,8].

A large part of Italy shows low disaster resilience [7,9,10] and the effects of a changing climate might be devastating for people and infrastructure; in this regard, adaptation to climate change (ACC) solutions are desirable. Disaster resilience has been explained through several concepts ranging from the “capacity of a system to endure exceptional occurrences” to “the capacity of a system to adapt to varying circumstances” [11]. In this study, we follow the Intergovernmental Panel on Climate Change (IPCC) and define disaster as “[severe] alterations in the normal functioning of a community or a society due to hazardous physical events interacting with vulnerable social conditions, leading to widespread adverse human, material, economic or environmental effects that require immediate emergency response to satisfy critical human needs, and that may require external support for recovery” [6] and resilience as “[the] capacity of social, economic and environmental systems to cope with a hazardous event or trend or disturbance, responding or reorganizing in ways that maintain their essential function, identity, and structure while also maintaining the capacity for adaptation, learning and transformation” [6].

The interest of institutions and the scientific community in the effects of climate change and adaptation strategies and measures has increased over time [12,13,14,15]. In this regard, the European Commission [14] adopted—and, in 2021, updated [15]—a strategy on adaptation to climate change. As a response, in 2015, the Italian Ministry of Environment adopted a National Climate Change Adaptation Strategy (NCCAS; Ministry of Environment [16]) and, in 2023, a National Climate Change Adaptation Plan (NCCAP; Ministry of Environment [17]). Adaptation objectives and measures ought to be sustainable to avoid maladaptation [18,19]. We define maladaptation as “action taken ostensibly to avoid or reduce vulnerability to climate change that impacts adversely on, or increases the vulnerability of other systems, sectors or social groups” [20] or, more recently, as “a result of an intentional adaptation policy or measure directly increasing vulnerability for the targeted and/or external actor(s), and/or eroding preconditions for sustainable development by indirectly increasing society’s vulnerability” [21].

ACC implies a wide range of solutions, including grey, green, and hybrid approaches [22,23]. As for the green approach, “ecosystems and their services […] can provide multiple hazard regulating functions such as coastal and surface flood regulation, temperature regulation and erosion control” [22]. Green infrastructure (GI), i.e., “strategically planned network of natural and semi-natural areas with other environmental features designed and managed to deliver a wide range of ecosystem services” [24], integrated into rural landscapes might contribute to making MAs more resilient to disaster. In Europe, studies show a certain relevance of GI as ACC measures (e.g., [25,26]); on the other hand, in Italy, according to the OECD, “green infrastructure (GI) and nature-based solutions (NbSs) are not yet fully integrated into spatial planning and projects’ appraisal instruments” [27]. This is critical as spatial planning and GIs are key tools to facilitate ACC [28,29].

Although the role of green infrastructure (GI) as an ACC strategy has gained a certain relevance worldwide, the scientific literature has scarcely addressed research on methods and guidelines for promoting the use of GI for increasing the disaster resilience of rural landscapes in Italian MAs. In general, De Montis et al. [30] remarked on the lack of methods aimed at drafting guidelines for the planning and design of GI. We note that the scientific literature is still lacking in research studies addressing the planning and design of tailored GI for MAs in a changing climate context. No previous research has focused on a method to set a reference scheme for the implementation of guidelines concerning the use of GI as an ACC approach to deal with the effects of a changing climate in Italian MAs. In this regard, this study is the first attempt to fill such a research gap in the realm of scientific research. Therefore, we aim to answer the following research question: can we propose a reference scheme for implementation guidelines that could be the basis for integrating GI and ACC in planning processes aimed at increasing the resilience of people and infrastructure against disasters? The aim is to provide planners and public administrations with an appropriate scheme to foster the mainstreaming of ACC into the planning process of Italian marginal areas. As this study is rooted in international publications (the scientific and grey literature), the reference scheme for implementation guidelines is potentially replicable in regions belonging to other countries that are characterized by institutional, climate, and geographical contexts similar to the Italian one. In other words, the reference scheme for implementation guidelines could be adopted by public bodies that are interested in promoting GI and ACC as a first step to allow MAs to be repopulated. To achieve our aim, we propose and apply a methodological approach consisting of the scrutiny of the scientific literature and grey literature (manuals, technical documents, guidance documents) to identify key elements (KEs) useful for integrating ACC and GI into planning tools.

This paper unfolds as follows. In Section 2, we provide definitions and elements that characterize the Italian marginal areas. In Section 3, we summarize research on the role of GI as an ACC strategy, as well as report practical examples. In Section 4, we describe the method, which provides the basis for the review of the scientific and grey literature. In Section 5, we apply the method and discuss the findings. In Section 6, we elaborate on the concluding remarks.

2. Marginal Areas in Italy

According to Barca et al. [2], ‘inner areas’ are those significantly distant from the supply centers of essential services (education, health, and mobility), rich in important environmental and cultural resources. About a quarter of the Italian population lives in these areas, which exceed sixty percent of the national territory [2]. The Italian National Institute of Statistics (Istituto nazionale di statistica; ISTAT, Italian acronym) includes in inner areas a preponderant part of the Italian territory, where ‘small urban centers’ most of the time can grant residents only limited access to essential services [31]. FORMEZ PA [32] considers inner areas as significantly distant from the main urban centers that provide essential services (education, health, and mobility) and have important environmental and cultural resources. The inner areas are identified among the municipalities lacking services according to a distance principle, which is understood as the travel time necessary to reach, by car, destinations delivering key educational, health, and mobility services [2]. The “peri-urban areas” are up to 20 min away from the “pole municipality”, the “intermediate areas” from 20 to 40 min, the “peripheral areas” from 40 to 75 min, and the “ultra-peripheral” areas over 75 min; only the last three categories are classified as “inner areas” [2].

The intermediate, peripheral, and ultra-peripheral municipalities are clustered into the group of inner areas [31]. Italian inner areas embrace around half of the Italian municipalities, mainly located in southern and insular regions [31]. Part of the municipalities in these regions are considered ‘ultraperipheral’. Ultraperipheral are those municipalities with a distance greater than the 95th percentile from the nearest ‘Pole municipality’ or ‘Intermunicipal Pole’. Pole municipality or Intermunicipal Pole jointly supplies three basic services: health, education, and mobility [31]. Marginal areas include, but are not limited to, inner areas; an area can be considered marginal for geographic reasons as well as development issues [33]. ‘Inner’ means that the areas are located in mountainous contexts, but, above all, they are far from the places of development and service networks [33]. Acierno [34] points out that the “processes of marginalization of our country’s inner areas [Italian inner areas] began in the first decades of the last Century and were initially characterized by ‘mountain depopulation’ [35], which was particularly accentuated after the First World War” [34].

Dezio and Paris [36] referred to MAs in terms of the contraction of utilized Italian agricultural areas, notable reduction in farms, and population decline in rural contexts: “This steady depopulation […] describes a framework of deep-rooted fragility that affects different rural areas in Italy, that we grouped and defined as “marginal”: peri-urban territories […]; mountain territories […]; inner areas […] and in-between Italy […]. This abandonment affects the territories as a system, and not only agriculture” (detailed references in Dezio and Paris [36]). In this research, we define marginal areas in a way that follows Mareggi [1], who defines MAs as contexts rich in natural resources that are characterized by a lack of infrastructure, are significantly far away from essential services, and suffer from sociodemographic and economic difficulties, such as depopulation, unemployment, and low incomes.

The National Strategy for Inner Areas (Strategia Nazionale Aree Interne; SNAI, Italian acronym) represents one of the national measures to combat depopulation and aims to counter the marginalization of the Italian innermost areas, with the purpose of promoting an improvement in demographic trends and stimulating the capacity of these areas to contribute to the processes of growth and national cohesion [37]. As part of the SNAI, Italian Law 205 of 2017 established a fund to support economic, craft, and commercial activities to be distributed among municipalities in inner areas by decree of the Italian Prime Minister [38]. In 2020, this fund was named Support Fund for Marginal Municipalities (Fondo di sostegno ai comuni marginali, in Italian). It aims to promote social cohesion and economic development in municipalities affected by depopulation and where there are significant shortcomings in attractiveness due to the reduced supply of tangible and intangible services to people and economic activities while respecting complementarity with SNAI [39]. Overall, EUR 180 million was allocated to 1187 municipalities for the time frame 2021–2023 (Figure 1). Note that other marginal municipalities are not included in those funded. Therefore, the map is purely illustrative as it refers to the time span 2021–2023.

3. An Overview of Green Infrastructure for Adaptation to Climate Change

In this section, we aim to remark on the relevance of GIs as ACC solutions. The purpose is to provide a research framework that supports this study. In other words, this section focused on the role of GI in promoting ACC. The emphasis is on ACC-GI-based measures, which might be part of a proposal of guidelines, but that are insufficient per se to increase the disaster resilience of specific institutional and geographical contexts.

The environmental policy of the European Union (EU) aims to preserve, protect, and improve environmental quality and protect human health [40]. Degradation and loss of natural or semi-natural habitats, climate change, and risks due to extreme weather events are central themes of European policies [41,42,43]. There is a growing awareness that nature, understood as a system of natural (and semi-natural) ecosystems and related ecosystem services, plays a key role in making a territory more resilient. In this regard, the so-called ‘nature-based solutions’ (NbSs) deserve to be mentioned within approaches to the ACC [44,45,46]. In this study, NbSs are defined as “[…] actions to protect, sustainably manage and restore natural or modified ecosystems, which address societal challenges (e.g., climate change, food, and water security or natural disasters) effectively and adaptively, while simultaneously providing human well-being and biodiversity benefits” [47]. NbSs are inspired, supported, or copied from nature [48]. They are based on the ecosystem approach that underlies the Convention on Biological Diversity ratified by Italy in 1994 [44,49,50]. NbSs can be grouped into five macro-categories [51] related to ecosystem restoration (e.g., forest landscape restoration), specific ecosystem interventions (Ecosystem-based Adaptation, acronym EbA), infrastructure interventions (Green Infrastructure, GI), ecosystem management, and ecosystem protection. NbS is an ‘umbrella concept’ that covers EbA, GI, and ecosystem services [44,46,52]. EbA specifically emphasizes the role of nature in ACC, while the concept of GI has emerged in planning theory and practice because it can foster the evolution of strategic approaches for the systematic integration of NbS and EbA in urban development at various scales [46]. GI can be defined as “a strategically planned network of natural and semi-natural areas with other environmental features designed and managed to deliver a wide range of ecosystem services. It incorporates green spaces (or blue if aquatic ecosystems are concerned) and other physical features in terrestrial (including coastal) and marine areas. On land, GI is present in rural and urban settings” [24]. GI provides a wide range of (provisioning, regulating, supporting, and cultural) ecosystem services [53,54].

It is well established that spatial planning and GIs (in addition to EbA) are key tools to facilitate ACC in various anthropized settings [28,29]. The role of GI in climate change mitigation and adaptation actions is also recognized by national and supranational public bodies (see, for example, [55,56]). Onuma and Tsuge [57] recalled that GI used for disaster risk reduction “can prevent multiple natural hazards, for example, as forests can prevent both landslides and floods” [57]. Even the European Environmental Agency [58] reiterated a similar statement: “[Green infrastructure], particularly forests but also other vegetation, can sizeably reduce [the] occurrence of shallow landslides” [58].

GI can be classified as urban or rural [59,60,61] and be beneficial to rural [62] and depopulated areas [63]. Aspacher and Alam [62] stressed the high costs and structural inefficiency of the traditional stormwater management methods while recalling the role of GI in mitigating stormwater runoff. GI absorbs water, which might “be reused throughout the natural hydrologic cycle” [62]. Blasi et al. [59] listed the benefits provided by GI in urban and rural contexts. As for the rural context, GIs have a positive role in soil erosion reduction, flood control, improved soil permeability, flood risk prevention, improved economy, and job opportunities (see the full list in Blasi et al. [59]). The implementation of GIs offers an efficient response against the effects of climate change and can contribute to improving people’s well-being [30].

Both the scientific and grey literature are rich in terms of GI solutions, which can be clustered according to the scheme reported in

Table 1. The most quoted green infrastructures that can be relevant to ACC by type, description, and references. Below, in Table 1, we stress the role and possible uses of GI in terms of ACC.

Type of GI	Description	References
Green corridors	They are avenues that allow animals to travel, plants to propagate, and populations to move in response to specific threats or environmental changes. They link natural areas in urban settlement.	[64,65,66,67,68]
Green bridges and eco-tunnel (or landscape bridges, or wildlife overpasses, or wildlife crossing structures, or wildlife crossing bridge)	They allow wild fauna to cross transport and mobility infrastructures.	[27,69,70]
Green noise barriers	They reduce urban traffic noise.	[27,71,72]
Urban forest	It is made up of the set of trees planted along avenues and in parks, up to and including entire wooded areas located both within the boundaries and around the city.	[67,73,74]
Terraces and slopes	They consist of an alteration of the slope shape, with the purpose of steepening one part of the slope (i.e., the riser) and reducing another part (i.e., the tread).	[67,75,76]
River and stream renaturation	They help addressing (mitigating) flooding risk through habitat creation, protection, or restoration.	[27,67,77]
Extensive and intensive green roofs (or biotic roofs)	A variable thickness package overlying a traditional roof and able to reduce water runoff and decrease heat island effect.	[67,78,79,80,81,82,83,84,85,86]
Ground-based green façades	They are composed of evergreen or deciduous climbers growing up the wall and sinking their roots into the soil next to the façades.	[67,80,81,87]
Façade-bounded greening	It is a green façade without the roots in the ground. The plants grow on particular thin layers of substrates, with purpose of reducing the weight of the green façade.	[67,80,81,87]
Open green spaces	They can be recreational (roof gardens, urban parks, botanical gardens, …), functional (administrative buildings, research areas, college campuses, agricultural lands, …), natural/semi-natural (coastline, wetlands, forests, …), etc.	[67,88,89,90]
Rain gardens	They are characterized by depressions in the ground, which collect rainwater runoff from impervious surfaces. The water stored in the depression tends to permeate slowly into the subsoil.	[91,92,93,94,95]

.

Below, we stress the role and possible uses of GI in terms of ACC. A green corridor “[…] can change the microclimate of the area and improve urban ventilation as they create a path for cooler air from outside to penetrate into the more densely built areas, also reducing the [Urban Heat Island effect]” [64]. It can also contribute to increasing permeability and reducing runoff in the context of water and flood management [65]. An example of a green bridge useful in terms of increasing resilience can be found in Natural England: “the design considered climate change resilience to match the water management on the green bridge with Intergovernmental Panel on Climate Change based climate scenarios of the Royal Dutch Meteorological Institute” [70]. The green noise barriers contribute to improving urban air quality [71]. Urban forests contribute to mitigating the heat island effect “by providing shade and by reducing urban albedo, and through cooling evapotranspiration” [74]. Urban forests contribute to controlling runoff due to storms and flooding “by catching rain in [the] canopies and increasing the infiltration rate of deposited precipitation. Reducing stormwater flow reduces stress on urban sewer systems by limiting the risk of hazardous combined sewer overflows” [74]. As for the terraces, they can be used “[…] to slow water down and provide areas for vegetation […]” [76]. River restoration is a technique aimed to reduce flooding risk. A green roof contributes to improving stormwater management, water run-off quality, and reducing the urban heat island effect. An extensive green roof contributes primarily to stormwater mitigation. An intensive green roof contributes primarily to stormwater mitigation, biodiversity, and amenity spaces, while “plants on a green façade can act as a rain screen and help decrease air and surface temperatures by canopy evapotranspiration and shading” [87]. Finally, open green spaces (e.g., parks) can contribute to mitigating the heat island effect [88], and rain gardens contribute to runoff storage and peak-flow reduction.

GI can also supply disservices [96], i.e., negative impacts on humans due to allergenic pollen, fungal spores, plants with thorns, plants with stinging hairs, and others (more details in Ćwik et al. [96]).

Solutions based on GIs can be useless as a way to address the effects of climate change if we do not provide them with a reference scheme for implementation through adequate guidelines. As the scientific literature has scarcely focused on reference schemes for implementation guidelines concerning the use of ACC-GI-based solutions in Italian marginal areas, we aim to fill this research gap. In this regard, in the next section, we propose a methodological approach with the purpose of supporting the implementation of GI by considering several elements emerging from the scientific and grey literature.

4. Materials and Methods

This section focuses on the methodological approach adopted for scrutinizing the scientific and grey literature to identify criteria for proposing a reference scheme for drafting ACC-useful GI implementation guidelines. We have been inspired by previous works based on the review of the scientific and grey literature [97,98,99,100,101] because our aim is to provide a reference scheme that is rooted in scientific bases, but that can be applicable in practice, i.e., in operational terms.

We considered the time span from 2013 —when the European Commission adopted the directive “Green Infrastructure (GI)—Enhancing Europe’s Natural Capital” [24]—to 2023. We extracted from Scopus and Web of Science the journal articles relevant to this research. We filtered the items by applying queries, such as “guidelines” AND “green infrastructure”, “green” AND “infrastructure” AND “guidelines”, “green infrastructure guidelines”, “guidelines for green infrastructures”, “green infrastructure guidance”, “green infrastructure” AND “adaptation”, and other similar matches; we sorted the publications by relevance [101]. We retrieved conference papers, manuals, guidelines, guidance documents, reports, and other publications that are part of the grey literature by filtering the Google search engine with the same queries. In total, Scopus (search within Article title, Abstract, Keywords) listed 2122, while Web of Science (search within: All Fields) listed 2787 journal articles. Note that the articles were sometimes redundant, i.e., the queries returned the same article(s). As for the grey literature, we did not impose any timeframe and did not count the number of publications as Google suggested too many web pages of references, which were challenging to consider (175 web pages).

As the issues actually covered by these publications are not fully relevant, we further filtered this dataset, following an approach inspired by Ray Biswas and Rahman [102], who excluded irrelevant items in subsequent selections by (i) titles and keywords and (ii) abstract or similar table of contents. Researchers specialized in ACC governance, GI planning and design, and spatial and landscape planning chose the most relevant publications for this study. The aim was to reduce subjectivity as much as possible. We also considered the Italian guidelines issued by Città Metropolitana di Genova e Università degli Studi di Genova—Dipartimento Architettura e Design—Scuola Politecnica [103] as we found the document was relevant to the Italian context. The aim was not to thoroughly review the literature on ACC and/or GI but to focus on studies and guidance documents considered useful in terms of drafting guidelines.

Finally, we focused on seventeen publications to identify key elements for designing ACC-useful GI guidelines, as described in

Table 2. The publications selected in this paper.

Scientific/Grey Literature	Title	Reference
Scientific literature	GI Guidelines for the Metropolitan City of Cagliari (Italy): A Method for Implementing Green Areas	[100]
	Integrating climate adaptation and transboundary management: Guidelines for designing climate-smart marine protected areas	[104]
	Barriers and guidelines for public policies on climate change adaptation: A missed opportunity of scientific knowledge-brokerage	[105]
	Increasing house owners adaptive capacity: Compliance between climate change risks and adaptation guidelines in Scandinavia	[106]
	Function-based and multi-scale approach to green roof guidelines for urban sustainability transitions: The case of Bogota	[83]
	Towards guidelines for designing parks of the future	[88]
	Looking to the future: guidelines for decision support as adaptation practice matures	[107]
	Guidelines for co-creating climate adaptation plans for fisheries and aquaculture	[108]
	The practice of settling and enacting strategic guidelines for climate adaptation in spatial planning: lessons from ten Swedish municipalities	[109]
Grey literature	Green Infrastructure Resource Guide	[110]
	Guidelines for Climate Change Adaptation in Brazilian Cities through Urban Green Infrastructure	[99]
	Infrastrutture verdi per l’adattamento ai cambiamenti climatici. Strategie e indicazioni progettuali per la gestione sostenibile delle acque meteoriche urbane nell’area mediterranea nord-occidentale	[103]
	Green Infrastructure Guide for Small Cities, Towns and Rural Communities	[111]
	Green Infrastructure. Guide for the Municipalities	[112]
	Design of guidelines for the elaboration of Regional Climate Change Adaptations Strategies	[113]
	Green Infrastructure Guide for Water Management: Ecosystem-based management approaches for water-related infrastructure projects	[114]
	Guidelines for co-designing and co-implementing green infrastructure in urban regeneration processes	[115]

.

5. Results and Discussion: Key Elements for Designing ACC-Useful GI Guidelines

In this section, we summarize and discuss the main findings distilled from the scientific and grey literature and point out key elements that should be part of a proposal of guidelines (

Table 3. Elements that can be relevant to drafting guidelines.

Code	Key Element (KE)	Description	References
KE1	Literature review	The literature review allows to identify the so-called state of the art. The literature review points out recent progress, critical issues, shared (or unshared) conclusions, etc., and it is the basis of documents rooted in scientific and technical considerations. Systematic analysis of the literature aids in identifying barriers that hinder ACC and overcoming them. The set of references needs to be listed as it provides the basis of the document and allows a reader to find details on specific topics.	[83,103,105,112,114]
KE2	Definition of green infrastructure, components and features of green infrastructure, main functions	The guidelines may include a brief framework which summarizes information on green infrastructure.	[103,112]
KE3	Consistency check	The guidelines should be consistent with European, national, and regional rules, norms, strategies, plans, guidance documents, etc.	[100,103,111]
KE4	Participative approaches	The participation of stakeholders should contribute to guidelines rooted in consensus and awareness. A preliminary version (draft) of the guidelines can be shared to capture different viewpoints and improve the document.	[83,88,108,113]
KE5	Public–private cooperation	Cooperation between public and private bodies is important to develop ACC guidelines that contribute to making information available and accessible, thus facilitating individual adaptive capacity.	[106]
KE6	Context-specific	The guidelines need to be adapted to the context, i.e., context-specific.	[83,99,100,103,107]
KE7	Concise, clear, and practical guidelines	The guidelines should use a plain (simple) language aimed at practitioners. Scientific knowledge must be translated for practitioners in transparent ways. A glossary/list of acronyms and/or abbreviation can also be adopted in the document. The use of practical examples or case studies can inspire practitioners, who are faced with problems already solved in other similar geographical and institutional contexts. Pilot application can be desirable.	[103,104,105,110,113,114,115]
KE8	Future climate scenarios	They are useful for considering future threats from climate change and prioritizing adequate protections.	[104]
KE9	Monitoring	Monitoring is useful to assess the performance of GI and adopt countermeasures if necessary.	[108,111]
KE10	Regular updating	The guidelines need to be regularly updated to integrate the most recent regulatory framework, research advancement, progress in daily practice, best practices, best available knowledge.	[107,109]

).

5.1. Key Elements from the Scientific Literature

Clar et al. [105] focused on barriers and guidance documents (decision-support frameworks) for public policies on ACC. The authors compared a set of guidelines against policy-related barriers that hinder ACC policymaking, which were distilled from the scientific literature. The authors identified sixteen key barriers, including a lack of political commitment, inadequate or unclear responsibilities, inadequate cooperation, no adequate technological solution available, and insufficient resources. They found out that “none of the guidelines […] address[ed] all or even a major part of the barriers identified” [105] because the guidelines lacked a systematic analysis of barriers (from literature review or empirical studies; Clar et al. [105]). Finally, Clar et al. [105] argued that “[if] guidelines are framed as knowledge-brokerage tools, relevant scientific insights have to be identified (or generated) and “translated” for practitioners in transparent ways” [105]. Arafeh-Dalmau et al. [104], who focused on guidelines and recommendations aimed at designing climate-smart networks of marine protected areas “with explicit integration of climate-change scenarios at ecoregional scales” [104], remarked on the need for practical guidelines. Arafeh-Dalmau et al. [104] also used future climate scenarios, which can be decisive in considering prospective threats due to climate change and prioritizing adequate protection.

Glaas et al. [106] analyzed the compliance between climate change risks and the ACC guidelines adopted in Denmark, Norway, and Sweden (Scandinavia), focusing on the adaptive capacity of the building stock. The scrutinized guidelines were drafted by insurance companies, government authorities, and municipalities. The authors found “that current guidelines often are built on experiences from previous weather impacts and are in this sense reactive, i.e., their development has been driven by experienced rather than expected impacts [and then] guidelines are generally less developed for how to mitigate future expected climate change risks” [106]. The authors argue that cooperation between public and private bodies is important to develop ACC guidelines that contribute to making information available and accessible, thus facilitating individual adaptive capacity (e.g., “the Danish government together with private actors has created widely distributed forums for spreading adaptation guidelines to some specifically targeted user groups” [106]).

Klemm et al. [88] stressed the key role of urban green infrastructure (UGI) as strategic ACC measures and addressed the design of “guidelines for climate-responsive UGI that stem from scientific knowledge and are useful to design practice”. Klemm et al. [88] aimed at developing design guidelines for climate-sensitive UGI that are useful in practice. They proposed and applied a methodological approach based on ‘Research through Designing’, which consisted of three steps: preliminary design guidelines, design practitioners’ assessment of the preliminary guidelines, and revision and improvement of the preliminary guidelines.

Ibáñez Gutiérrez and Ramos-Mejía [83] focused on the Bogota Biotic Roof Guidelines, which were drafted in four steps: literature review, debate with local government authorities, submission of the draft to stakeholders, and acquisition of opinions and definition of alternatives for the construction of guidelines based on consensus.

Palutikof et al. [107] summarized the main insights from eleven papers addressing ACC “from the perspectives of adaptation platform and decision support tool developers” [107]. To do so, the authors distilled ten guidelines clustered into three groups: foundational; design and construction; and long-term sustainability. The guidelines included the so-called ‘one size does not fit all’, meaning that the tools designed to support ACC “should be context-specific […]” [107] (see also [108]) and the need for regular updating of decision support tools or adaptation platforms to “ensure continued relevance and sustained viability, and hence user confidence in the long-term and ongoing usage” (see Palutikof et al. [107], for more details and the full list of guidelines). Storbjörk and Uggla [109] pointed out similar considerations, arguing that the “planners further see any guideline for climate change as temporary as they have already witnessed them being gradually sharpened and in constant need of updating following best available knowledge” [109].

Calia et al. [100] pointed out the lack of scientific literature concerning methods for drafting guidelines aimed at supporting the public administrations in the implementation of GI. Thus, the authors proposed and applied a methodological approach to the design of GI guidelines for the Metropolitan City of Cagliari (Italy). The method consisted of three phases: context analysis, as objectives and measures need to be shaped to meet specific requirements due to the type of context; consistency check, as the objectives of the guidelines have to be consistent with the sustainability framework (i.e., sustainability objectives established from international to regional scale); and a draft of the guidelines, with a focus on the inclusion of key elements distilled from the grey literature.

Pham et al. [108] proposed guidelines consisting of a detailed step-by-step approach aimed at drafting ACC plans in the fishery and aquaculture systems. This approach is based on the continuous involvement of different types of stakeholders (co-creation approach) throughout the planning process (e.g., scoping of the plan, ranking risks and opportunities, etc.), which contributes to making the planning process more transparent and can help in reaching a consensus. As an example, the role of stakeholders is relevant to define the scope and aims of the plan, assess the risks and opportunities, and identify adaptation (much more details in [108]).

5.2. Key Elements from the Grey Literature

Ribeiro et al. [113] drafted a policy guidance document “intended to assist regional authorities and other regional bodies in charge in formulating [Regional Adaptation Strategies]”, which was based on the contents of thirty-one regional adaptation strategies (adopted in France, Germany, Netherlands, the UK, Spain, and Sweden), an analysis of previous guidelines released for drafting ACC strategies, and stakeholders’ participation. Ribeiro et al. [113] identified five key factors for a successful Regional Adaptation Strategy: meaningful and sustained stakeholder engagement; use and dissemination of appropriate information; awareness raising; monitoring, evaluation, and review; and successful management of multi-level governance. In terms of concrete adaptation measures, Ribeiro et al. [113] recalled three typologies: grey infrastructure, GI, and soft, non-structural approaches: “Green infrastructure is using the functions and services provided by ecosystems to achieve more cost-effective and sometimes more feasible adaptation solutions” [113]. The guidelines proposed by Ribeiro et al. [113] are rich in practical examples and suggestions, including a glossary clarifying the meaning of technical terms (such as adaptation, climate scenario, vulnerability indicators, etc.) and a list of criteria for evaluating the effects of adaptation actions.

According to the United Nations Environment Programme (UNEP acronym), “spatial planners, engineers and decision-makers are eager to identify and utilize cost-effective, long term and environmentally appropriate infrastructure solutions” [114]. UNEP released a guide to improve the awareness of GI solutions and related cost-benefits. The guide branched off into six main sections supplemented by references: introduction; key water resources management issues addressed by GI solutions; GI solutions for water management; methodology for water management options assessment; practical tools for quantification and valuation of benefits; and benefits, barriers, and the possible way ahead [114]. The guide recalled solutions also useful in rural areas, such as “[in] situ water harvesting practices [that] usually contribute to soil conservation through preventing soil erosion and soil loss, thus providing better conditions for crops and other vegetation in the area [which are relevant to] increased food security and resilience to droughts as well as reduced need for irrigation water and energy use for water transport” [114] and related costs. The guide also provides a matrix [114], which includes GI solutions depending on the context (watershed, floodplain, urban, and coastal). As an example, in non-urban contexts, with a focus on moderation of extreme events (floods), the guide suggests afforestation, re/afforestation, forest conservation, wetlands restoration/conservation, constructing wetlands, riparian buffers, establishing flood bypasses, reconnecting rivers to floodplains, etc. Re/afforestation, riparian buffers, and reconnecting rivers to floodplains are also relevant to erosion control (reinforcement of slopes, in terms of corresponding grey infrastructure solution).

In September 2017, AECOM [110] released a guide for the United States Agency for International Development (USAID), which needed guidelines to support the planning and design of GI, which can be included in projects. The main sections of the guidelines covered an introduction to GI interventions and GI considerations depending on different settings and scales [110]. The document defined acronyms and provided the reader (practitioner) with definitions of key terms such as GI, indicator, rain gardens, peri-urban agriculture, etc. The guide encompassed a variety of topics, for example, “Erosion control”, “Rural flood mitigation”, and “Managing soil and slope stabilization after wildfires”.

The Greenbelt Foundation published, in 2017, a GI guide for small cities, towns, and rural communities [111]. The guide included four sections: “Overview of Green Infrastructure Types and Their Functions”, “Introduction to Planning Zones”, “Green Infrastructure Opportunities for Each Planning Zone”, and “Green Infrastructure Types in More Detail”. The guide emphasized the prevailing availability of studies and guidelines on GI for densely populated urban contexts compared to “smaller and rural settlements […] despite the many benefits that green infrastructure can provide in these settings” [111]. The document is intended as support to stakeholders, including planners and developers, and clearly remarked on the key role of GI in terms of climate change resiliency planning. Overall, the guide considers seventeen types of GI, which are “suitable for built areas of smaller cities, towns and rural communities” [111] and that include hedgerow, perforated pipe, riparian buffer, etc. The guide points out three key considerations regarding each type of GI: maximize benefits (specific goals, needs, and climate conditions have to be considered); maximize efficiency and effectiveness (elements such as place and design need to be considered); and monitoring (to assess the performance of GI and adopt countermeasures if necessary).

Hudeková [112] remarked on the role of the local level (e.g., municipality) for the implementation of GI and drafted a guide for municipalities to foster the comprehension of GI into practice. The guide consisted of six main sections: “What is green infrastructure?”, “The application of the concept of green infrastructure”, “Main functions of green infrastructure”, “Components and features of green infrastructure”, “How to elaborate the Strategy/Action plan for green infrastructure in municipalities”, and “Funding possibilities for green infrastructure”. An appendix and a rich bibliography supplemented the guide. The author stated that “[green] infrastructure can be divided according to different criteria. The basic categorisation presents a breakdown into urban and rural green infrastructure […]” [112]. As regards ACC, the guide recalled both the EU Strategy on green infrastructure [24] and the EU Strategy on Adaptation to Climate Change [14], which “highlights the role of green infrastructure and the provided ecosystem services and nature-based solutions” [112]. According to Hudeková [112], GIs have a variety of environmental and ecological functions, such as improvement of air quality and microclimate in urbanized settings, ACC, and “regulation of soil erosion and other slope processes [landslide risk prevention]”. As components of GI in rural areas, Hudeková [112] referred to, inter alia, protected areas, restored biotopes, wetlands, natural meadows, windbreaks, hedgerows, solitary trees, forests, and wildlife crossing structures (eco-ducts or eco-bridges).

The metropolitan city of Genoa (Italy) [103] drafted guidelines concerning GIs for ACC, which focused on strategies and design guidance for sustainable urban stormwater management in the northwestern Mediterranean area. The guidelines consist of four main sections that regard climate change and urban environment, GI (benefits and ecosystem services, EU community policies and international and national examples of guidelines, etc.), fact sheets for the design of stormwater management systems (rain garden, infiltration basin, vegetative swale, and green roof), and a case study (an example of rain garden). The guidelines are bilingual (written in Italian and French), rich in terms of scientific and technical references, accompanied by illustrations concerning the design of GI in practice and photos that clarify the case study. The guidelines also provide a list and description of the species adopted in the rain garden (Astelia banksia, Carex secta, Ceanothus spp, Chasmanthium latifolium, Cotoneaster dammeri, Festuca actae, etc.). Technical drawings (plant and section) of the rain garden supplemented the case study.

Almeida and Engel [99] considered the role of Urban Green Infrastructure for ACC in Brazil and settled guidelines to reduce the vulnerability of the cities. The authors developed the research in four steps: “systematic review elaboration […] document selection and identification of risks […] document selection and evaluation of the green infrastructure applicability in the urban context […] connections between risks and green infrastructure” [99]. Almeida and Engel [99] emphasized that it is necessary to choose solutions suited to specific local issues.

Wilk et al. [115] proposed guidelines aimed at providing “practical guidance for setting up organizational and administrative structures suited to the planning and execution of local [Nature-based Solutions] co-design processes”. Wilk et al. [115] remarked on the need for concise and practical guidelines, which should be written in simple and clear language to be understood by practitioners.

5.3. Key Elements: Summary

Table 3 lists some elements that should be relevant to drafting guidelines. The key elements (KEs) include literature review (KE1), clear definition of GI (KE2), consistency check (KE3), participative approaches (KE4), public–private cooperation (KE5), context-specific (KE6), conciseness and practical use (KE7), future climate scenarios (KE8), monitoring (KE9), and regular updating (KE10).

Below, we summarize and discuss the KEs.

5.3.1. Literature Review (KE1)

A proposal of guidelines, as intended in this paper, should be rooted in scientific and technical bases (KE1), according to a twofold approach. Snyder [116] argues that “[using] literature review as a methodology has a high potential to make a substantial contribution to theory, practice, or policy” [116]. In this study, we follow Snyder [116] and argue that the scientific literature can provide guidance and suggestions concerning the advancement of research worldwide in a variety of fields, and a proposal of guidelines should lie on shared key factors usually useful in several contexts, e.g., clear definition of GI, participative approaches, and inclusion of practical examples. On the other hand, the grey literature has a practical role as it is often the result of interactions between public and/or private bodies that work in actual scenarios. Practical guidelines need to consider specific normative requirements, climate conditions, latitude, and other characteristics of the urban, peri-urban, or rural context where a system of GI could contribute to increasing disaster resilience. The suggestions retrieved from the grey literature may help to translate theoretical guidance into operational strategies and measures. Furthermore, the systematic analysis of the scientific and grey literature has the potential to identify barriers that hinder ACC and overcome them. A literature review is often time-consuming and demanding in terms of analytical skills (see also for suggestions [116,117]). We are aware that public administrations may not be able to perform a literature review due to a lack of expertise and financial resources to hire qualified officials.

5.3.2. Definition of Green Infrastructure, Components and Features of Green Infrastructure, and Main Functions (KE2)

The wide variety of definitions of GI [118] has pros and cons [119,120]. The pros include, for example, that the term’s flexibility has contributed to increasing GI appeal, while the cons are that the same flexibility “can lead to frustration and greenwashing, where broken promises of multi-functionality sour public opinion and leave cities vulnerable to the threats GI was supposed to address” [120]. In this regard, we feel that a clear definition of GI (KE2) would allow—in and for a specific context—interested parties to fully understand what a GI and related ecosystem services are. Once the parties agree on the meaning of GI—its components, features, and main functions—then the stakeholders involved in the planning, design and decision-making, and implementation process, from the public bodies to citizens, can communicate on common ground. In other terms, the use of a shared and clear definition of GI may avoid misunderstandings on their potential use and limitations.

5.3.3. Consistency Check (KE3)

The consistency check (KE3) allows the guidelines to be coherent with European, national, and regional sustainable and ACC objectives as well as normative and planning issues. This is relevant to integrate ACC and GI considerations according to a top-down approach, with the purpose of promoting the mainstreaming of ACC from strategies to operational measures that are consistent with supra-ordinate plans and programs or directives. In this regard, a proposal of guidelines could integrate “sustainability objectives” [100] that set a framework for sustainable ACC strategies, objectives, and measures to avoid maladaptation, i.e., to promote sustainable adaptation [18].

5.3.4. Participative Approaches (KE4)

The participative approach (KE4) is commonly adopted to integrate public perspectives into the planning and programming processes in a variety of contexts [98,121] with different effectiveness [121]. Dorst et al. [122] identified barriers, i.e., project-level problems, to urban NbSs, including difficulties in citizen engagement that depend on different reasons (e.g., lack of resources and NIMBY syndrome). The authors argue that “[in] order to function well, [Nature-based Solutions] need to be brought into alignment with local environmental, physical and social contexts, which requires a level of citizen engagement” [122]. As GIs are part of NbSs, we speculate that a bottom-up approach could allow the public to express criticism, suggestions, or advice against issues not enough—or not at all—considered by who is responsible for drafting the guidelines. In this regard, a preliminary version (draft) of the guidelines can be shared to capture the different points of view and improve the document [83]. However, the technicalities and complexity of the topics (ACC and GI) might be unfamiliar to people without adequate technical, regulatory, or specialist skills, and public participation would be useless.

5.3.5. Public–Private Cooperation (KE5)

Cooperation between public and private bodies (KE5) is important to develop ACC guidelines that contribute to making information available and accessible, thus facilitating individual adaptive capacity (e.g., by spreading ACC guidelines to specific user groups). As an example, relevant actors might be government authorities, municipalities, and insurance bodies [106].

5.3.6. Context-Specific (KE6)

Context-specific guidelines (KE6) are often thought to be more effective than those based on vague and purely theoretical and general guidance (e.g.,: [98,123]). We agree with this point of view. The guidelines could include a general part that encompasses European, national, and regional frameworks and a specific part that points out remarkable peculiarities concerning the subregional scale, e.g., type of landscapes and hydrogeological, climate, and other characteristics. In other words, the guidelines might include landscape fact sheets (e.g.,: [124]) and climate scenarios (historical climate data and climate forecasts) set on a sub-regional scale, with the purpose of defining potential GI-based solutions, which will be detailed and operationalized at a municipal scale.

5.3.7. Concise, Clear, and Practical Guidelines (KE7)

The guidelines should be concise and practical (KE7). This is a well-known suggestion [88,104,105,115]. We mean ‘concise’ as free of redundant information and ‘practical’ as a translation of suggestions into feasible/realistic ACC measures. As an example, if the guidelines suggest using GI to reduce/avoid the negative effects of floods and landslides, then they should also provide a set of operative measures that can be adopted in practice (e.g., conservation/implementation of forest covers, increase the surface occupied by green spaces, strengthening the greenery in public parks, increase the areas occupied by green roofs, promote the creation of urban gardens, promote the participation of citizens in the care of public green areas, etc.). The inclusion of practical examples can inspire practitioners who are faced with problems already solved in other similar geographical and institutional contexts. The practical examples should be retrieved from actual case studies or GI projects already adopted. The guidelines may refer to the practical examples in an ad hoc section, which provides the reader with adequate references. As an example, this section could include the name of the project/case study, year of implementation, geographical context, main characteristics of the project/case study, type of climate disaster considered (e.g., floods, landslides, drought), type of GI adopted, and cost. Finally, the use of a glossary/list of acronyms helps to increase the conciseness of the guidelines.

5.3.8. Future Climate Scenarios (KE8)

Future climate scenarios (KE8) can be useful for considering future threats from climate change and prioritizing adequate protections [104]. Some researchers have pointed out that future climate scenarios can be used for assessing “the impacts on GI performance” [125] and the cost-effectiveness of GI in the realm of ACC [126]. However, climate model projections have practical limitations due, for example, to deep uncertainty and natural variability [127]. A proposal of guidelines may include—or suggest the inclusion in plans and programs of—future climate scenarios, although we are aware these may be unavailable at local scales and may be devoid of reliable and detailed data.

5.3.9. Monitoring (KE9)

Monitoring (KE9) is relevant to assess the performance of GI and adopt countermeasures, if necessary [111], e.g., it helps us to understand if adaptation works are fruitful or not [102]. Monitoring relies on the use of quali-quantitative indicators, which “reduce the complexity of data, simplify interpretations and assessments and facilitate communication between experts and non-experts” [29]. The guidelines may suggest a set of indicators for assessing the effectiveness of GI in terms of increased resilience against the effects of climate changes (e.g., temperature moderation by evapotranspiration and shading, wind speed modification, control, flood reduction, etc.; see [29]).

5.3.10. Regular Updating (KE10)

Regular updating (KE10) of the guidelines is necessary to consider recent regulatory frameworks, research advancement, progress, and best practices [107,109]. Non-updated guidelines may include references to outdated documents, repealed laws, and links to offline websites. In the worst case, the guidelines become useless.

6. Conclusions

In this study, we aimed to set a scheme for implementation guidelines concerning the use of green infrastructure (GI) as an adaptation to climate change (ACC) approach to increase the disaster resilience of Italian marginal areas (MAs). Thus, we identified and proposed ten key elements (KEs) that constitute a reference scheme for GI implementation guidelines. The KEs distilled from the scrutiny of both the scientific and grey literature are aimed at introducing GI and ACC in a GI planning and design process. We found out that the elements relevant to drafting guidelines are (i) solid scientific and practical bases, (ii) clear definitions of the term GI, (iii) coherence against European, national, and regional strategies and objectives, (iv) stakeholder involvement, (v) cooperation between public and private bodies, (vi) the need to meet local problems through ad hoc solutions, (vii) conciseness and practical examples to support practitioners, (viii) the inclusion of future climate scenarios, (ix) the monitoring phase and indicators, and (x) regular updating.

This study has limitations that future research should address. First, the KEs have not been tested in practice, and we are not aware of their effectiveness in an actual scenario. However, as the methodology adopted in this study is rooted in international publications, the KEs are reasonably applicable in other contexts. In this regard, scholars may find, in this study, one of the first attempts to propose the use of GI as an ACC strategy to contribute to repopulating MAs. Second, the capacity to introduce the KEs in a proposal of guidelines can be challenging depending on the type of KE we consider. For example, some KEs are likely to be addressed at a regional scale (e.g., literature review; definition of GI, its components, features, and main functions; consistency check, etc.), where more resources are available (data, information, fundings), while other KEs are addressed at a local scale (context-specific guidelines; monitoring; etc.). Ongoing collaboration between regions, municipalities, and other relevant stakeholders would, therefore, be desirable to define guidelines that are reasonably useful.

Future research needs to address the practical application of the KEs in an actual GI planning and design process and answer questions concerning the barriers to the full implementation of the KEs, the main obstacles, and the pros and cons. In this regard, we will be addressing the practical application of the KEs in a case study in Sardinia (Italy).