Building Climate Resilience in Coastal City Living Labs Using Ecosystem-Based Adaptation: A Systematic Review

Abstract

Climate change leads to an unequivocal rise in the intensity and frequency of natural disasters. This necessitates mainstreaming of climate adaptation strategies in the global movement on climate action. Ecosystem-Based Adaptation (EBA) has become popular as an effective means of climate adaptation, which can be resilient and flexible compared to hard engineering-based measures. However, ecosystem-based approaches in disaster risk reduction still remain under-researched despite their growing popularity. This study delves into the utility of EBA in the context of the living lab, using a PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) based Systematic Literature Review. A living lab (LL) is a participatory tool invented to foster innovation through real-life testing environments, such as individual cities. This study focuses on European coastal regions, as these are both highly populated and vulnerable to climate change impacts such as sea-level rise, storms, flooding and erosion. This study identified multiple synergies between the EBA concepts, living lab and disaster-risk reduction and concludes that EBA schemes can be highly effective in the living lab set-up. It also demonstrates that increased stakeholder engagement and the consideration of socio-economic co-benefits as part of the EBA-LL model can lead to successful disaster risk reduction.

1. Introduction

Highly urbanized coastal cities are not only densely populated but also economically pivotal, making them extremely important regions. In light of the increased frequency and intensity of coastal natural hazards in the face of impending climate change, these coastal cities are under an imminent threat. Increased coastal storms, flooding, erosion and sea-level rise in coastal regions have made the study and implementation of efficient coastal adaptation strategies imperative. Innovative adaptation schemes such as ‘ecosystem-based adaptation’ (EBA) have become popular as a resilient and effective means of coastal adaptation [1].

Research has found that nature-based adaptation strategies such as EBA can be extremely effective at addressing hydro-meteorological disasters, including floods, storms, erosion and more [2]. Natural hazards that originate from atmospheric, hydrological, or oceanic processes that cause substantial socio-economic disruptions and devastation, such as loss of human life, services, livelihoods, property, and the environment, are classified as hydro-meteorological risks [3]. These caused roughly 90,325 fatalities in Europe between 1980 and 2017 and accounted for about 80% (502.56 billion USD) of the total economic damage caused by natural hazards (618.5 billion USD) (EEA, 2019). Amongst hydro-meteorological risks, coastal floods and coastal storms have been two of the biggest threats [3]. Research found that EBA strategies can, in several cases, more effectively address these hydro-meteorological risks when compared to traditional engineering-based infrastructure [1].

Nature-based adaptation strategies such as EBA, when combined with participatory approaches can provide a unique and innovative model for climate adaptation. However, their implementation has been limited due to a lack of understanding of the interaction between EBA and participatory approaches [4,5,6]. Several European Union (EU) projects, including OPERANDUM, RECONECT, GREEN SURGE and NAIAD [7,8,9,10] amongst others, have started analyzing the role of EBA in climate adaptation using the living lab (LL) approach, but pertinent research gaps are yet to be addressed [11].

Living Labs (LLs) can be an effective participatory approach to address these gaps through their ability to create real-life testing environments [12]. They have become increasingly popular as ‘innovation ecosystems’ that can address complex challenges. Due to their strong focus on user participation, LLs have become an important component of smart cities in Europe [12]. Coastal City Living Labs (CCLLs), developed as part of the EU SCORE project, are based on the LL concept, but focus on co-designing and co-developing coastal city interventions through novel EBAs. CCLLs have been implemented to tackle specific challenges related to sea-level rise and extreme weather events.

Studying the role of EBA in the context of the CCLL, we also delve into the overlapping concept of nature-based solutions (NBS). NBS are sustainable solutions that are in harmony with nature, cost-effective and provide environmental as well as socio-economic benefits [13]. EBA encompasses NBS strategies specifically aimed at climate adaptation. EBA involves the management of ecosystem services to reduce the vulnerability of human communities to the impacts of climate change [14]. The Convention on Biological Diversity (CBD) defines EBA as “the use of ecosystem services to help people to adapt to the adverse effects of climate change” [15]. EBA is nested within the broader concept of NBS, which essentially corresponds to the sustainable management and use of nature to tackle socio-environmental challenges such as food security, water pollution, biodiversity and climate change [13] and includes concepts such as Blue-Green Infrastructure (BGI), Ecosystem-Based Disaster Risk Reduction (Eco-DRR), Urban Living Lab (ULL), and more. Figure 1 illustrates a timeline of the important concepts reviewed in this article. It also demonstrates the new and innovative nature of the ‘CCLL’ concept, which has been coined in 2021.

It is noteworthy that whilst the main focus of EBA is climate change adaptation, NBS can address a wide range of sustainability challenges [16]. The terms EBA and NBS have been used synonymously in this paper, but it is important to keep this difference in mind.

The key research gap that this paper addresses is the role of NBS in the context of LLs in order to achieve successful climate adaptation/disaster risk reduction (DRR). This paper has focused exclusively on ‘urban’, ‘coastal’ and ‘European’ areas, as these are the parameters of the CCLLs being developed as part of the EU SCORE project. The past and ongoing research within the European context provide a significant foundation upon which further research can be carried out, as has been performed in this paper. European coastal cities have also provided a unique and challenging research environment, as many are economic and cultural hubs that are under imminent threat from sea-level rise. This paper has focused on building climate resilience through studying innovative EBA-based DRR strategies (specifically focusing on hydro-meteorological risks such as floods, storms and erosion) in these European CCLLs.

Ultimately, this paper delves into the role of stakeholder engagement as well as interlinked socio-economic issues in these CCLLs, specifically in the context of successful EBA implementation. This is an important research area. Several authors, e.g., [7,17], have determined that effective stakeholder engagement is key to the success of EBA. However, research on the exact relationship between stakeholder engagement and EBA implementation is extremely limited [11]. Stakeholder engagement is also a key component of the process of co-creation and co-production of knowledge part of the LL approach. Therefore, the study of stakeholder engagement is key to increasing our understanding of the synergies between NBS and LL. This has been explored as part of this paper.

The main research objectives addressed in this paper include: (i) analyzing the role of LL in building climate resilience, (ii) studying the role of NBS/EBA in building coastal resilience, (iii) addressing the linkages between NBS and socio-economic issues in the LL, (iv) studying the relationship between stakeholder engagement and the NBS-LL model and (v) studying the synergies between NBS, LL and DRR.

A systematic literature review has been undertaken using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) methodology, to address these research objectives. Based on an initial screening of 892 peer-reviewed articles, this paper finally makes use of 62 articles as part of its systematic review. The results are presented in seven sections, and then discussed and analyzed in order to address the research objectives.

2. Methodology

This review paper used the systematic literature review procedure as part of its research methodology. Two databases (Science Direct and Web of Science) were selected for the review process. A ‘search string’ was created using the following keywords: ALL= ((ecosystem-based adaptation OR nature-based solutions) AND (living lab OR living labs) AND (coastal OR coast) AND (socio-economic OR socio-economic OR stakeholder) AND (climate)). This search string was applied to the two databases, and while Web of Science yielded 820 results, Science Direct yielded 88 results. Initially, the registers CORDIS (Community Research and Development Information Service) and Climate-Adapt were also being considered for the review but were ultimately not included due to the large number of results already available via Web of Science and Science Direct. Figure 2 depicts the most recurrent terms found in the titles of all the 908 articles reviewed in the databases.

The two databases have been filtered/screened with the primary eligibility criteria defined in

Table 1. Inclusion and exclusion criteria as part of the PRISMA-based systematic review.

Criterion	Eligibility	Exclusion
Timeline	2008–2021	Pre-2008
Language	English	Non-English
Type of Publication	Empirical Studies, Conceptual and Grey Literature.	News, non-empirical studies.
Environmental Issue	Climate change adaptation related	Non-climate change adaptation related.
Geographical Context	Coastal and urban areas (‘living labs’)	Non-coastal and rural areas
Spatial Scale	European	Non-European
Type of Assessment	Socio-economic	Non-socio-economic

. The timeline 2008–2021 was selected because the term ‘nature-based solutions’ was coined in 2008 [18]. The search had been limited to Europe, to the category of ‘environmental science/environmental studies’, and to ‘urban’ and ‘coastal’ areas only. The studies have been selected based on the following keywords: living labs, socio-economic, ecosystem-based adaptation, nature-based solutions, stakeholder engagement and climate.

The PRISMA methodology were used to conduct the systematic literature review. PRISMA is a set of evidence-based reporting elements for systematic reviews and meta-analyses. PRISMA is intended to report reviews that evaluate the effectiveness of interventions, but it can also be used to report systematic literature reviews with other objectives. PRISMA is part of a larger strategy to enhance research quality and improve the reporting of several types of research. Table 1 depicts the inclusion and exclusion criteria part of the PRISMA-based methodology.

The initial identification of studies had been made by applying the following filters: search string, language (English), timeline (2008–2021), and peer-reviewed records. Duplicate, unreadable references and unpublished records were removed. This yielded a total of 908 results. The second stage involved: (i) screening based on title and abstract and (ii) full-text screening of the papers selected in the first stage. Finally, in the third stage, the final database of 62 papers is divided into seven sections. These include-Living Labs, Ecosystem-Based Adaptation, Nature-Based Solutions, Coastal/Urban Areas, Disaster Risk Reduction, Socio-Economic and Stakeholder Engagement. The numbers in the brackets next to these sections represent the number of papers per section. The process has been illustrated in Figure 3, the ‘Prisma Diagram’.

3. Results

The 62 papers that were ultimately selected for the systematic literature review, were then studied and analyzed. Since this paper brings together an array of concepts (including LL, NBS, EBA, DRR, and so on), it is important to study the interlinkages between these concepts and analyze any trends. This is what this section aims to do.

In order to find any significant trends amongst the selected 62 papers part of this review, we look at the following data:

• Years of Publication

Figure 4 indicates that while publications on this topic started in 2008, when the NBS concept was first coined; publications only started increasing after 2016 and went on to rise significantly in the years 2019 and 2020. There was a slight dip in the year 2021, most probably owing to the Covid-19 pandemic.

• Countries of Publication

Figure 5 highlights the number of Publications Per Country (in Europe). This figure indicates that Sweden, UK and Germany are the countries with the highest number of publications. The blue circles represent the countries that have been studied as case-study sites as part of the articles selected in this systematic literature review. These countries include: Sweden, Norway, Finland, United Kingdom, Denmark, The Netherlands, Germany, Belgium, Poland, Bulgaria, Italy, Spain, France, Portugal, Greece, Turkey, Czech Republic and Slovenia. The size of the blue circle represents the higher number of case studies from that specific country. Sweden, Germany, Italy and the UK have the highest number of case studies with 6 cases from Sweden; 5 cases from Germany; and 4 cases from Italy and the UK each. There is a significant overlap with the map on overall articles selected as part of this review, as Sweden, the UK, Germany and Italy were also among some of the countries that had the highest number of publications.

• Journals of Publication

Looking at the numerous journals that have been included as part of this review, it was found that environmental journals such as ‘Sustainability’ and ‘Environmental Science and Policy’, ‘Climatic Change’, and ‘Water’, have some of the highest publications. This is what Figure 6 illustrates.

• Type of Study/Research Method

Figure 7 indicates that case studies were the most used research methodology, followed by literature reviews. Framework analysis and systematic literature reviews jointly share the third spot at 14.5%. Participatory analysis tools (such as living labs) and modeling were the least used methodologies, at 9.7%.

• Systematic Literature Reviews included in this article

Table 2. Systematic Literature Reviews included in this article.

Paper Title	Articles Reviewed	Key Findings
Systematic Review of Smart Cities and Climate Adaptation [6]	282 articles	The concept of synergetic coproduction has identified benefits that coexist in smart city and climate adaptation. While smart people and smart government are the most important aspects of smart cities, synergy has been developed in other areas. Smart city applications in adaptation to climate change have boosted cities’ competitiveness by maximizing possibilities while minimizing dangers.
Effectiveness of EBA for adaptation: a review of the evidence base [18]	132 articles	The study found that climate variability and extremes have taught us a lot about EBA. Most measures of their effectiveness described in the publications revealed encouraging findings. Most papers cited the social, environmental, and economic benefits of EBA initiatives, and if drawbacks were mentioned, they were only briefly.
Towards an operationalization of NBS for natural hazards [19]	250 articles + 53 reports	The technique of NBS operationalization was investigated and reported in detail for five different HMHs (floods, droughts, landslides, coastal erosion and storm surge, sediment loading), with seven EU-OALs as examples. For each hazard category, historical and predicted trends in HMHs were examined, and the value of their information in the NBS planning and operationalization process was discussed.
NBS for hydro-meteorological risk reduction: a state-of-the-art review of the research area [11]	146 articles	This work consisted of a critical evaluation of the literature on NBSs for reducing hydro-meteorological risk and identifying current knowledge gaps as well as future research opportunities. Scientific papers in this area have increased significantly, with a more substantial increase beginning in 2007.
An overview of monitoring methods for assessing the performance of NBS against natural hazards [7]	262 articles	This work has contributed to the wider use of NBS by compiling a knowledge base on their monitoring methodologies, efficiency, functionality, and ecosystem services. This was accomplished by analyzing the existing scientific literature on NBS performance in the face of five HMRs: floods, droughts, heatwaves, landslides, storm surges, and coastal erosion.
Stakeholder engagement on NBS: a systematic literature review [20]	142 articles	The present state of the art in public and stakeholder participation in nature-based solutions was investigated in this systematic literature review (NBS). Stakeholder participation in nature-based solutions was acknowledged as beneficial, although research in various linked sectors is still insufficient.
A review of public acceptance of NBS: the why, when and how of success for disaster risk reduction [21]	99 articles	Through a comparison with grey measurements, the unique qualities of NBS in regard to public acceptance were investigated in this paper. Risk perception, trust, competing societal interests, and ecological services were all highlighted in the PA-NBS model. It was argued that increased acceptability should be based on giving and promoting benefits, as well as good communication and teamwork.

highlights the key findings from the important systematic literature reviews included in this article, including containing the number of articles reviewed per paper. As part of these review papers, a total of 1366 articles have been reviewed.

• Frameworks included in this article

Table 3. Frameworks included in this article.

Framework	Article Title	Use
NBS Co-Benefit Assessment Framework [22]	A framework for assessing and implementing the co-benefits of nature-based solutions in urban areas	Within ten difficulty areas, a framework was developed for evaluating the benefits and costs of NBS. In other challenge areas, advantages in one challenge area may have costs, co-benefits, or neutral impacts. This aided in the development of a multi-sectoral strategy to environmental management.
NBS Applicative Framework (based on DPSIR) [23]	Nature-based solutions: settling the issue of sustainable urbanization	A framework for investigating the effects of NBS on urban dynamics. NBS was a category of downstream measures that city leaders and legislators were using to enhance sustainable urbanization.
Dynamic Adaptive Policy Pathways [24]	Paving the way to coastal adaptation pathways: an interdisciplinary approach based on territorial archetypes	Six territorial archetypes characteristic of French coastal territories made up this exploratory modeling framework. For each typology, the framework highlighted separate and shared resources. A generic framework was used to build the adaptation pathways, which included three elements: the archetype’s configuration and specificities, the possible evolution of change variables for each archetype based on available experiment findings and assumptions about sea-level rise.
The THESEUS Approach: the Source-Pathway-Receptor-Consequence model for coastal risk assessment [25]	Coastal flood protection: what perspective in a changing time? The THESEUS approach	This model was providing a comprehensive technique for planning long-term coastal flooding and erosion defense plans that consider technological, social, economic, and environmental factors.
Optimization framework for GBI selection [26]	Exploring trade-offs amongst the multiple benefits of green-blue-grey infrastructure for urban flood mitigation	This framework was developed for identifying and analyzing blue-grey-green initiatives that take into account co-benefits and trade-offs.
EBM Ranking for Flood-Prone Coastal Areas [27]	Ranking coastal flood protection designs from engineered to nature-based	This framework was used to classify and rank coastal flood prevention designs as nature-based, with options ranging from fully designed to wholly natural. Flood-prone locations along the North Sea coast were studied using the EBM approach.
Framework for adaptable socio-hydrology (FrASH) [28]	Situating Green Infrastructure in Context: A Framework for Adaptive Socio-Hydrology in Cities	This framework was helping with NBS planning and implementation. It also helped governments, organizations, and stakeholders build a connected network.

highlights the most important frameworks that have been studied as part of this review article. Many of these frameworks are unique and innovative and specifically created to increase our understanding, improve our assessment, and develop effective selection tools for NBS as well as build effective pathways for coastal adaptation and coastal flood protection in the face of climate change.

After analyzing these important trends, this section has divided the 62 review papers into seven categories: (i) Living Labs, (ii) Nature-Based Solutions, (iii) Ecosystem-Based Adaptation, (iv) Coastal/Urban Areas, (v) Disaster Risk Reduction, (vi) Stakeholder Engagement and (vii) Socio-Economic Impacts.

3.1. Living LABS

ALL is a user-centric ecosystem that operates within a geographical context (e.g., a city or region), and integrates ongoing research and innovation within a public-private-citizens partnership [12]. LLs appeared in 2000 in private firms as real-life testing environments for Information and Communication technologies [12]. In the context of nature-based climate adaptation, the whole city is viewed as a living laboratory where citizens and stakeholders are proactively involved in the process of designing, implementing and testing innovation [29]. This section focuses on the role of LL for EBA.

LLs involve the concepts of ‘co-creation’ and ‘co-production’, which have now also become popular in climate adaptation literature [2]. Co-creation has proven to be extremely useful in the context of climate change because it suggests that both the local government and the community play a critical role in climate adaptation [2]. This proposes a form of collaborative governance for EBA, a concept also highly synergetic with the LL approach [30].

Ref. [4] has argued that developing ecosystem services in conjunction with NBS and LL can build more resilient cities. However, implementing NBS in LLs is also a challenging process [5]. This is because the integration of diverse actors’ efforts and capacities is a challenging task. Another hindrance comes from the fact that both the NBS and LL concepts focus on human-environment interactions and are usually not based on current executive and legislative structures [5]. A lack of empirical research on the effectiveness of urban LL also hinders their successful implementation. Nineteen address the challenging relationship between NBS and climate adaptation through empirical research in five LLs established in Sweden (Malmö, Lomma, Eslov, Hoganas and Kristianstad) from 2017–2019. They found that municipal staff and citizens pursue five essential tactics to overcome obstacles in the face of NBS implementation in the LL. These include (i) internal cooperation structure modifications, (ii) focused stakeholder collaboration, (iii) targeted public involvement, (iv) hidden science–policy linkage, and (v) outsourcing. In addition to this, ref. [2] led another case study in eight municipalities in the Bavarian region of Germany (München, Nuremberg, Regensburg, Würzburg, Landshut, Passau, Deggendorf and Freising). The authors found that the division of responsibility between city authorities and the citizens can often be ambiguous in a living lab structure. Nevertheless, the importance of handing over more responsibilities to citizens for effective climate adaptation was recognized. This study also observed that in some cases, citizens in the LL can hamper each other’s efforts towards adaptation through a lack of mutual support.

Along different lines, ref. [6] found that participatory approaches such as LL support synergetic coproduction that offers multiple co-benefits apart from climate adaptation (e.g., the establishment of a smart city, improved quality of life, job satisfaction, and increased adaptive ability). In the context of climate uncertainty, the same author suggested that an LL-based strategy for climate adaptation is required to make effective judgments. Moreover, they stated that climate-related concerns frequently affect many sectors, hence necessitating interdisciplinary tools such as the LL to address them [6].

To add to this, ref. [4] carried out a study to identify the stages, stakeholders, strategies and tools for EBA in LLs through the Life-Cycle Co-Creation process. They listed the most important sectors (academia, industry, public sector, and civil society) as well as the most important stakeholders (innovators, financers, end-users, problem owners, and so on) as part of the LL structure. In addition to this, they also provided a list of the roles important for LL implementation, including project manager, living lab manager, pilot manager, and so on. This has been illustrated in Figure 8. Their framework can prove to be useful for implementing EBA in LLs.

Along similar lines, ref. [31] stated that EBA is intricately linked with the LL approach. This is because, in several cases, NBS has served as a platform for knowledge co-creation, enabled social inclusivity, and supported collaborative governance, which are essential components of the LL approach. Moreover, LLs have immense potential to deal with several constraints inhibiting urban EBA (e.g., lack of discourses and support, limited awareness, and low attentiveness in the planning system), thus supporting its wider uptake. Ref. [31] also found a strong need to support EBA at a local level, which is exactly what LLs can do. Through the LL platform (as part of the EU Green Surge project), it became possible to have important discussions with diverse practitioners from different European cities- which aided adaptation planning.

To add to this, ref. [32] developed a value-based framework to facilitate stakeholder engagement in NBS planning as part of the EU UNALAB project. Given how the multifunctionality, context-specificity and co-benefits make it difficult to capture the overall value of NBS, this framework has been extremely useful. This framework was developed using data from the following living labs: Cannes, France; Stavanger, Norway; Castellon, Spain; Prague, Czech Republic; and Basaksehir, Turkey. The respondents felt that the framework might be useful for: raising awareness about NBS amongst urban planners; better network management; stakeholder collaboration; and communication in a standardized language.

Ref. [30] found that an open approach to collaborative governance and co-creation can encourage the adoption of NBS in urban LL. Their research was conducted in nine European cities, namely Antwerp, Belgium; Bristol, UK; Katowice, Poland; Malmo, Sweden; Vejle, Denmark; Potenza, Italy; Ioannina, Greece; Glasgow, UK; and Rotterdam, the Netherlands. Four NBS-based experiments were set up between 2016–2018 in the nine LLs. This included in-person interviews with urban planners, participant observation groups, and workshops to discuss lessons learned. They found that experimenting with NBS requires trust in the local government as well as a unique form of collaborative governance; that NBS should be designed in a manner that it can be replicated in a long term and easily incorporated amongst urban agendas; and that its co-creation requires learning from social innovation.

In synergy with this, ref. [19] studied NBS in the context of Open-Air Laboratories (OAL) (a form of LL). They stated that the OAL can be used as a model for scaling up NBS for DRR. While many authors [33,34,35] claim that NBS can be effective for DRR, few offer a framework for implementation. In this context, ref. [19] developed a framework for the operationalization of NBS within a LL setting. It includes the following steps: identification of hydro-meteorological risks such as floods, and coastal storms); risk assessment through impact modeling and evaluation; selection of the most suitable NBS strategy (green, blue, hybrid); implementation of the NBS as well as socio-institutional measures; co-development (stakeholder mapping, problem framing, etc.); monitoring and evaluation of the NBS schemes; and development of policy frameworks. The absence of science-based proof of NBS’ effectiveness is one of the numerous problems impeding its implementation.

To conclude, our understanding of innovative approaches, particularly bottom-up initiatives with their various actors and how they complement nature-based adaptation planning, is relatively scarce. This emphasizes the need for transdisciplinary approaches to better understand opportunities and constraints within fields of practice, which is what the living lab approach aims to do. However, despite some successes, the actual performance of LL in the context of climate change has been uncertain due to the lack of empirical evidence.

3.2. Nature-Based Solutions

Climate change has been causing a rise in the intensity and frequency of extreme weather events, especially in coastal regions. These include sea-level rise, coastal storms, floods and erosion, amongst others. NBS such as beach nourishment, vegetated roofs/walls and sea dikes can effectively contribute to addressing these coastal hazards [36]. NBS refers to the long-term use of nature to address socio-environmental challenges such as climate change [13]. The term ‘Nature-Based Solutions’ was first used by the World Bank in 2008 and then promoted by the IUCN (International Union of Conservation of Nature) in the consecutive year [14].

Ref. [37] found that the NBS concept has a strong footing in the European context (46%) and urban areas (57%) (which is the focus of this study). Coastal flood mitigation has been one of the key motivations for implementing NBS, and their popularity has grown due to lower prices and flexibility compared to hard-engineering-based infrastructure. Ref. [1] argued that the NBS concept’s strength is in its integrative, systemic approach, which keeps it from becoming just another green communication tool. They also found that NBS provides an opportunity for transdisciplinary research. In contrast to this, ref. [37] stated that 59% of the papers in their review showed low-level integration of the NBS concept, with the term being used mostly as a buzzword. Most studies only looked at the environmental benefits of NBS, not considering the socio-economic benefits. Another challenge for an umbrella concept such as NBS has been where to draw the line on what is considered ‘natural’ [1]. Through empirical research based on workshops with experts from seven European countries, ref. [38] determined that to achieve mainstreaming of the NBS concept, there is a: (i) stronger need to produce evidence on NBS for climate adaptation; (ii) need for adaptation to governance challenges; (iii) considering the role of socio-economic co-benefits while implementing NBS.

Numerous publications have tried to bridge the aforementioned research gaps. Ref. [22] studied the role of NBS co-benefits to guide cross-sectoral policies. A review of 1700 publications across ten key societal challenges was conducted to develop this framework. This framework consisted of seven steps: identification of problem, selection of NBS, design NBS implementation process, implement NBS, engage stakeholders, upscale NBS, evaluate co-benefits across all stages. Along similar lines, ref. [39] studied the role of NBS in urban areas. They identified a taxonomy of major hurdles to NBS implementation in urban settings, focusing on the governance challenges to NBS implementation in urban regions. A literature review and expert interviews resulted in the identification of fifteen significant impediments: among them were lack of political will, lack of urgency amongst officials, and lack of public knowledge. The authors also utilized integrative structural modeling to study the interaction between these obstacles. Ref. [36] stated that classifying NBS solutions into high-tech, low-tech and no-tech can assist with effective NBS implementation. Ref. [40] developed a framework for the evaluation of NBS schemes in urban areas. Their viewpoint was that NBS implementation is challenging due to a lack of proof of its impact. Conceptual issues about the assessment of implemented NBS were discovered during a thorough investigation, namely: absence of systematic mapping of synergies and trade-offs between different categories of NBS impacts; mixing of process and results (indicators) in evaluating NBS; lack of analysis of pathways by which NBS affect.

To conclude, the popularity of NBS has grown rapidly in the past decade. Its role has increasingly been recognized in urban areas and also for flood mitigation-2 criteria important to this review paper. Whilst the EU has achieved much to promote NBS in Europe, there is still a need for stronger integration of this concept. To realize the full potential of NBS, the integration of stakeholders has been important.

3.3. Ecosystem-Based Adaptation

Ecosystem-Based Adaptation refers to the sustainable management of ecosystem resources in a manner that alleviates climate change impacts [14]. These approaches have become popular over the last decade as an effective alternative to hard or engineering-based approaches to climate adaptation.

EBA can be important to both climate adaptation and disaster risk reduction, both of which largely overlap. Ref. [16] classify EBA according to their risk-reduction capacities as follows: (i) keep hazards away from communities; (ii) vulnerability reduction to allow communities to live with hazards; and (iii) preparedness for response to cope with climate hazards. Ref. [41] carried out a literature review to study the effectiveness of EBA. It was found that EBA measures often have social and economic co-benefits along with environmental benefits. However, they do not effectively conduct a cost-benefit analysis for the same. In particular, the role of EBA for DRR was also not discussed enough.

Ref. [42] stated that there is still limited literature on the inclusion of EBA measures in climate adaptation plans at urban levels. They developed a framework to address this. However, the most effective EBA-related research has been carried out through the implementation of case studies. Ref. [16] investigated how EBA is incorporated into municipal policies and planning in four coastal, metropolitan Swedish towns. According to [16], the majority of EBA initiatives in these four municipalities were connected to biodiversity protection (32%), with only 6% related to climate adaptation. Furthermore, present policies were unsuccessful in addressing risk factors while also supporting ecosystem services. They reached the conclusion that integrating EBA into local planning requires a more methodical approach.

Ref. [43] looked at how EBA was implemented in twelve German and Swedish towns. While there were certain similarities in the way both countries implemented EBA measures, there were also notable variances. EBA was frequently regarded as a part of ‘ecosystem services’ in Sweden, and hence its links to climate mitigation/adaptation were overlooked. Climate mitigation, on the other hand, was a top priority in Germany. Ref. [43] classified seven options for mainstreaming EBA in climate policy, resulting in an extremely effective framework. It was ultimately concluded that there is a need for research on the linkages between climate policy and EBA, to facilitate its mainstreaming.

Taking a different approach, ref. [44] studied the role of EBA specifically for DRR. It was proposed that coordinating EBA efforts for climate adaptation and DRR can result in significant co-benefits. Stakeholders and funders were attracted when co-benefits were demonstrated. Although EBA and DRR have certain similarities, there are also differences. While climate-related disasters normally necessitated long-term planning, DRR primarily focused on immediate threats. In synergy with this finding, ref. [16] studied EBA measures across 112 cities/urban areas and found rapid growth in their importance, primarily due to the higher costs and inflexibility of hard-engineering-based measures. Whilst most articles focused on flooding as the main risk, the research was fragmented due to different disciplinary backgrounds. However, several articles implied that EBA measures are increasingly being integrated into DRR schemes.

To conclude, EBA can play a crucial role in climate adaptation and DRR-especially in coastal and urban European areas, as highlighted through the above-mentioned case studies. Like NBS, EBA also has significant co-benefits for society and the economy, and its successful implementation requires effective stakeholder engagement. Overall, although EBA is being increasingly integrated into institutional structures, there is still limited literature on the adoption of EBA in local governance strategies as well as a lack of systematization of EBA.

3.4. Coastal Cities

Coastal cities have been significant centres for habitation, industry, agriculture, trade, and tourism, to name a few. As economies have developed, the challenges along coastal cities have also increased, including sea-level rise, storms, flooding and erosion. Climate change has further exacerbated these challenges, and current coastal management strategies are not well equipped to handle these [25]. Large stretches of European coastlines are already exposed to risk. Deltas, low-lying coasts, islands, beaches, wetlands and estuaries around Europe are already affected by a rise in sea levels [25]. In this context, academics have started emphasizing the value of natural coastal features. However, examples of NBS coastal DRR schemes are few and certainly not mainstream [45]. The relative lack of perceived scientific efficacy makes these approaches less attractive.

The layered and intricate nature of population demographics in coastal cities- including diverse economic and social groups- has added to the challenge. In this context, numerous studies have found that NBS has positive effects on the reduction of flood risk in coastal cities, e.g., [39,40,41,42,43,44]. In addition to this, ref. [46] found that NBS can reduce urban surface run-off by 15% compared to grey infrastructure. However, the selection of the most effective type of NBS remains a challenge to urban planners.

To overcome this problem, ref. [23] proposed a robust NBS framework based on the DPSIR (Drivers-Pressures-State-Impact-Response) model. Ref. [23] also created the THESEUS framework after conducting research in eight European locations. This framework assessed coastal risk using the Source-Pathway-Receptor-Consequence model to also assist with the selection of the most effective NBS. Ref. [24] created yet another framework, employing an innovative archetypal framework to investigate adaptation pathways to climate change in coastal locations. Their research aided in the successful management of coastal adaptation in unpredictable environments.

Ref. [47] studied the role of NBS in alleviating coastal storms and flooding in conjunction with engineering-based infrastructure. They suggested the following NBS: soft solutions in conjunction with hard solutions; morphological and hydrological changes be mitigated; hard coastal constructions be ecologically enhanced. Local environment and socio-economic factors have heavily influenced the selection and success of these components. Ref. [48] investigate the ecological value of sea dikes, which are essential for preserving low-lying coastal areas across the world. Sea dikes are typically made up of hybrid constructions: vegetation and grey infrastructure. A total of 1200 km of sea dikes safe-guard a population of 2,400,000 people in Germany. However, there has been little research on the effect of NBS on sea dikes, and there are significant knowledge gaps. Multidisciplinary collaboration between engineers and ecologists has become increasingly important to close this gap.

Coastal dunes are equally significant in reducing coastal hazards. According to [49], coastal dunes operate as a barrier to storm surges and wave winds, minimizing flood and coastal erosion. The previous study investigated the function of coastal dunes in catastrophe risk reduction along the rapidly eroding coastline in Bellochio, Italy. Under current conditions, the planned dune system resulted in a 22% increase in DRR, and between 57% and 82% under future sea-level rise scenarios for low to high RCP (Representative Concentration Pathways) scenarios, respectively.

To conclude, the role of NBS has increasingly been recognized in urban and coastal areas. Even though coastal regions have been adversely affected by rapid urbanization and climate change, numerous studies indicate the potential of NBS for coastal hazard and flood mitigation. Although there are still knowledge gaps and implementation challenges, researchers are developing effective frameworks to address these. On the other hand, numerous scientists, ecologists and engineers are also developing practical tools such as sea-dikes, dunes and hybrid infrastructures to address sea-level rise, flooding and erosion.

3.5. Disaster Risk Reduction

The ongoing climate crisis has caused a dramatic rise in extreme weather events around the world [3]. NBS has recently received considerable attention in response to this phenomenon as they can effectively address natural hazards and generate co-benefits.

Ref. [11] conducted intensive systematic literature on the role of NBS for DRR. NBS can help reduce the risk of storm surges, wave energy, coastal flooding and erosion in coastal areas (see, for example, [50,51,52,53]). They investigated the role of small and large-scale NBS. Dunes, beaches, oyster and coral reefs, mangroves, seagrass beds, and marshes are examples of small-scale coastal NBS interventions. To date, various types of small-scale NBS have been investigated with the goals of reducing the flood peak [54,55,56,57,58], postponing the flood peak [59], and reducing the volume of sewer overflows.

Although the implementation of large-scale NBS for flood reduction has been limited due to factors such as higher costs and infrastructural barriers, numerous case studies have demonstrated their potential for example, [60,61,62]. The Sponge City Programme in China and the Room for the River Programme in the Netherlands have been two of the most effective international case studies demonstrating the potential of large-scale NBS. The Room for the River Programme studies 39 projects combining nine types of NBS measures, inter alia, floodplain lowering, dyke-relocation, summer-bed deepening, groyne lowering, water storage, and dike-strengthening [10].

Ref. [10] used the platform of the EU RECONECT project to perform research on large-scale NBS in two catchment areas in the Portofino National Park (Italy). This is an area of significant social, environmental, and economic value that has been endangered by flash floods, storm surges, hyper-concentrated floods, erosion, and landslides, among other hazards. The Portofino NBS case study has produced a number of benefits and co-benefits, including: (i) reduced geo-hydrological vulnerability; (ii) effective hydro-meteorological risk monitoring; (iii) efficient management of dry-stone walls to aid in the restoration of old gardens and re-incentivized agricultural processes; (iv) cultural heritage protection; and (v) reduced effects of landslides caused by coastal erosion. Several studies showed that large-scale NBS can dramatically change run-off in urban areas and is more efficient at long-term flood mitigation [63]. Though the data is clear on the effectiveness of large-scale NBS, further research on the role of hybrid NBS (NBS combined with traditional engineering) is needed [11].

Apart from studying the role of large and small-scale NBS, ref. [11] also looks at the most effective frameworks for the evaluation of NBS. These included hydraulic models, cost-benefit analysis, multi-criteria analysis, multi-attribute utility theory, relative performance evaluation, and qualitative methods. In addition to this, ref. [17] evaluated 1834 publications to investigate people’s perceptions of NBS’s involvement in DRR. Prior flood damage experience, personal risk perception, future flooding dread, and a coping appraisal were some of the key aspects that influenced people’s ‘risk perception’: The value of NBS co-benefits, the evaluation of risk reduction efficiency, stakeholder participation, socio-economic conditions, environmental attitudes, and uncertainty were some of the primary subjects explored in this article.

One of the most important publications in this line of work is that of [7]. They stated that there is an absence of universally standardized methods for monitoring NBS. They attempted to fill this gap by reviewing the literature on ground-based methods and remote sensing observations. They discovered that aerial and satellite-based remote sensing technology is quite successful, but that it must be tailored to the unique NBS. Ref. [7] developed the following methodology for NBS monitoring: (i) Natural hazard detection, (ii) NBS intervention, (iii) NBS monitoring, (iv) Evaluation, and (v) Decision-making. The indicators, also known as Key Performance Indicators (KPIs), are based on both hydro-meteorological hazards and impacts (biophysical, sustainability and socio-economic).

When it comes to floods, ref. [7] discovered that the effectiveness of a flood control system is highly dependent on the type of flood. [64] considered hybrid flood prevention systems to be the most effective. Wave height, velocity, and direction; storm characteristics (duration, surge, height, wind intensity, direction); vegetation/coral/oyster coverage, type and topography; and bathymetry were some of the most useful methods for monitoring storm surges and coastal erosion [7]. Whilst [65] demonstrated that salt marshes are effective in reducing wave height and energy from 60–80%, authors such as [66,67] demonstrated the role of dunes. Ref. [27] conducted a global analysis on the role of mangroves, seagrass/kelp beds, and coral reefs for wave height reduction from 52 projects in various global habitats.

Shifting our focus from technical aspects to policy, ref. [68] studied the role of governance mechanisms in implementing EBA for DRR. Governance theories, socio-ecological systems, and multi-level politics are all part of their analyses. A paper by [69] found that mainstreaming EBA into policy is a governance challenge. Ref. [68] argued that whereas most research focuses on governance difficulties (money, bureaucratic capacity, political jurisdiction, corruption, etc.), their focus is on governance potential. Economic, institutional, spatial planning and implementation, emergent innovation and technology, and socio-political processes are all examples of these. The primary governance ideas used for EBA were adaptive management, climate change and risk governance, transformational governance, environmental economics, and governance of socio-ecological processes.

To look at this from a different angle, ref. [8] studied the role of the insurance industry in ecosystem-based DRR. This report described the findings of comprehensive literature analysis and 61 stakeholder interviews as part of the EU NAIAD project. Grounded Theory-based methods showed how this sector can help with nature-based DRR and loss avoidance. The findings contributed to a broader discussion in Europe about the cost of avoiding damage from green preventive measures. This research was significant because it has been established that natural disaster damages will increase in Europe. In France, for example, if no preventive steps are taken, insured property damage has been predicted to increase by 50% [8]. The study also revealed that implementing NBS measures in the insurance industry is considered significantly more burdensome. Whilst 67% of the interviewees said they had no plans to incorporate NBS into risk models, only 15% of interviewees had explored this option [8].

To conclude, as climate change exacerbates natural hazards, NBS will play a critical role in mitigating disaster risks. While [11] demonstrates the efficacy of large versus small-scale NBS for DRR, other authors share case studies [10] wherein NBS was used for reducing risk from natural disasters. Different articles studied the role of NBS in DRR from different vantage points. Ref. [7] analyzed the different monitoring methods to assess NBS; Ref. [68] reviewed the governance of EBA for DRR; and ref. [8] studied the role of the insurance industry in eco-DRR.

3.6. Socio-Economic

Although it has been widely acknowledged that the success of NBS projects is dependent on socio-economic benefits, most NBS assessments continue to focus solely on environmental benefits. According to [70], this is because NBS initiatives have been usually constructed by ecologists and biologists versed in a different scientific worldview and hence communicating in a different language than decision-makers and citizens.

According to [71,72], implementing NBSs that have tangible benefits for the city’s resilience and liveability has often inspired stakeholders and citizens. Furthermore, because NBS measures frequently necessitated an investment, stakeholders must be aware of their utility [73]. It is critical to consider socio-economic uncertainty within the framework for flood mitigation to effectively apply NBS. Ref. [74] established a framework for adaptable socio-hydrology (FrASH) that may be used in NBS planning and implementation. The framework has also helped governments, organizations, and stakeholders build a connected network.

In addition to this, an article by [75] examined whether adaptation responses in coastal areas are ‘robust’, by focusing on the extent to which they reduce socio-economic vulnerability. This article was authored as part of the EU CLIMSAVE project, and case studies from Switzerland, Norway and Scotland were studied. The results showed that People-based Adaptation was the most effective of all the archetypes. This reduced vulnerability by increasing people’s adaptive capacity through education and building networks.

Ref. [28] conducted the first assessment of floods in the EU in the context of the socio-economic effects of climate change. The evaluation was split into two categories: no adaptation and adaption. Flood inundation maps were combined with susceptibility levels to assess socio-economic damage. Under the no-adaptation scenario, yearly flood damages of €5.5 billion could climb to €98 billion annually by the 2080s. Floods presently affect 200,000 people annually in the EU, but this number is anticipated to climb to 360,000 persons annually by 2050. Despite the fact that flood damage in Europe has been quantified in numerous IPCC (Intergovernmental Panel on Climate Change) assessments, ref. [28] were among the first to have assessed their socio-economic impact. The goal of this evaluation was to see how future climate and socio-economic changes will affect future flood risk in Europe, and how much it will cost to mitigate the negative effects through adaptation. Even though the population of the UK, Ireland, Belgium, France, the Netherlands, Austria, Finland, and Italy is declining, ref. [28] concluded that floods would harm a greater number of people (100-year forecast) in these nations due to a rapid rise in flood events.

They also stated that it is harder to address socio-economic problems compared to technological ones. This is because socio-economic challenges include perception, legislation, the multidisciplinary dimension of NBS implementation, education, and the documentation of the economic effects of NBS implementation [76]. Nonetheless, scientific research has helped understand the hurdles faced as part of NBS initiatives and gain insight into a community’s needs and risk perception [76]. Moreover, there are few case studies that have examined NBS politics in relation to community mobilization [68]. Involving stakeholders in selecting, planning, designing, and implementing NBS has been critical for bridging gaps.

Ref. [17] conducted a systematic review which found merely ten publications relating to socio-economic conditions and NBS. They discovered that people’s views of NBS were exceedingly diverse and inconsistent as they were influenced massively by context. The same study also found that characteristics such as education levels and financial robustness shape perceptions of NBS. According to [77], the quantity of household income and government subsidy were both connected to the level of support for NBS projects. This connection, however, only applied to low-income homes. Other investigations have discovered that a preference for NBS can be location-dependent. People’s attachments to the project site also played a role in this. A few studies discovered evidence that stakeholders’ attitudes regarding NBS were influenced by their environmental attitudes. People who reported higher levels of environmental concern, for example, favored NBS over traditional flood management methods. A preference for NBS was interpreted in another study as evidence of benevolence: participants picked NBS despite obtaining no personal benefit because of “the degree of environmental quality offered” and “the act of giving” [17].

Another systematic evaluation was undertaken by [78] to study the role of EBA strategies for social empowerment. They believed that there is a dearth of theoretical and empirical understanding of how EBA techniques disrupt power relations in society, particularly their impacts on marginalized groups. In the academic literature on adaptation, social empowerment has received relatively little attention exceptions are [79,80,81]. NBS has grown to prominence due to its ability to produce win-win results [82,83].

Engineering-based solutions are starting to be seen as less inclusive than NBS. Due to the heavy reliance of marginalized communities on the local ecology for their livelihoods, it is believed that EBA is particularly well suited for this purpose [84]. Both EBA and NBS have a number of co-benefits, many of which are socio-economic in nature [85,86]. The argument that EBA can provide social advantages for underprivileged populations has been intriguing from the standpoint of empowerment [84]. Despite the fact that these statements have become more common [41], their empirical validity has received limited attention [16]. In this context, ref. [77] studied the interlinkages between EBA and empowerment. They discovered that EBA provides a variety of social advantages, including being a pro-poor approach linked to climate-affected livelihoods, being a participative, inclusive, and regionally sensitive approach, and addressing the ecological basis of people’s vulnerability.

In order to build a framework for the socio-cultural valuation of NBS, ref. [87] gathered information from 200 citizens in Rotterdam, the Netherlands. This study analyzed concerns about climate consequences, their acceptance of NBS, and their choice of varied NBS measures, including their willingness to pay (WTP). Among the main results, it was found that while most citizens were aware of climate challenges, they were unaware of the function of NBS in minimizing these effects. Whilst environmental education helped support NBS measures, their WTP was ultimately affected by income levels and ethnicity.

To conclude, although the research on the linkages between socio-economic issues and climate adaptation is limited, studies have found a correlation between increasing climate-related natural hazards and socio-economic vulnerability. The work by Rojas et al. (2013) on the socio-economic effects of floods is very insightful in this regard. A comprehensive analysis of systematic reviews, empirical research as well as frameworks indicates that incorporating socio-economic wellbeing while framing climate policies is key to their success.

3.7. Stakeholder Engagement

Stakeholder participation has been highlighted as an important component of DRR processes and NBS implementation. It is important to include the stakeholders that will have been affected by NBS projects in the decision-making. In this regard, ref. [88] conducted a study to analyze the role of stakeholder engagement in NBS projects. The review identified (a) stakeholder perceptions and viewpoints; (b) the participation process, which includes obstacles and incentives, methodologies and structures, and collaborative governance. The study indicated that although stakeholder engagement in NBS initiatives is increasingly recognized as important; there are still pertinent research gaps.

Although authors such as [88,89,90] studied the role of stakeholder engagement in NBS implementation, these are mostly focused on urban green spaces and city liveability, and do not incorporate a comprehensive study of NBS. Refs. [91,92] found that citizens prefer biophilic designs that enhance spatial experiences and aesthetics. The main problems mentioned by stakeholders when assessing perceived NBS challenges included a lack of: information, political backing, finances, evidence of efficacy, and so on. Stakeholders also identified numerous opportunities and benefits from NBS, such as social cohesion, environmental education, connection with nature, conflict prevention, increased biodiversity, and so on.

Ref. [17] found that although stakeholder participation was touched upon in 12 of the 102 studies reviewed as part of their systematic review, it was never the main focus. They found that efficient communication and trust amongst stakeholders increase local ownership of these initiatives. For example, in the Netherlands, people’s trust in regional Dutch groups enhanced support for NBS, as found during the Room for River Program. Citizens and stakeholders play a critical role in ascertaining the public acceptance of NBS projects. Ref. [65], as part of the EU OPERANDUM project, studied the increasing role of public participation in addressing flood risks, as codified in the EU Water Framework Directive. They found that though negative perceptions of NBS hamper their successful implementation, on the other end of the spectrum, stakeholder participation ensures their success.

Despite the fact that public participation is a goal of NBS initiatives, stakeholder engagement is rarely based on a thorough understanding of the elements that influence public perception. The majority of NBS research has concentrated on its physical execution rather than local views, while the latter is gaining more recognition [68]. Due to a lack of social science research, expectations may be mismatched, and communities may be blamed for project failures. Ref. [21] argued that the shift from traditional grey infrastructure towards NBS is increasing the reliance on public acceptance. Ref. [27] suggested that a loss of public trust in decision-makers, as well as increased demands for transparency, has fueled a growth in public participation. Ref. [5] also stated that the reason for more citizen involvement in NBS is a paradigm shift toward coexistence with nature. Although the exact necessity and character of public acceptance vary depending on the setting, it is nonetheless critical for the success of NBS programs, as numerous authors have indicated.

In their systematic review of 5900 articles, ref. [21] identified key characteristics of NBS and how they related to public acceptance. They found that the most commonly accepted NBS measures in urban settings were found in Europe, whilst nearly half of the articles reviewed were situated in coastal regions. The most common natural risks were classified as flooding, erosion, storm surges, and cyclones, among others. Ref. [21] also found that public acceptance is generally more important in the case of NBS than for grey measures. In the case of NBS measurements, acceptance is also linked to upscaling and repetition. While 59 papers discussed the impact of co-benefits in promoting public acceptance, ref. [21] found that perceived levels of risk also influenced the public acceptance of NBS. They listed the following characteristics as criteria that boost trust in NBS: egalitarian, multi-functional, evidence-based, culturally meaningful, value-framed, clear and consistent.

Ref. [93] conducted a study on stakeholders’ preferences for governance approaches for EBA. Results from 251 questionnaires indicated that most respondents preferred an EBA strategy for DRR over conventional ones. The findings indicated an evolutionary approach to flood management, in which new paradigms emerge. In contrast to these literature reviews, ref. [94] conducted an empirical study in 2014 in Basque County, Spain, where a workshop was held to study climate adaptation. The views of participants from academia, private enterprises, and the public sector indicated that NBS-related measures were the most effective for climate adaptation, as they were less expensive and provided co-benefits, offering a win-win situation. Among different adaptation measures, early warning systems and coastal defences against flooding were mentioned in the workshop and EBA measures were also preferred due to their positive socio-economic outcomes.

Ref. [95] studied the role of stakeholders in co-production in municipal adaptation planning. Synergies, mismatches, impediments, and driving forces in the co-creation process were found based on a participatory analysis of two municipalities in Germany and Sweden. Looking at another empirical study, ref. [96] studied stakeholders’ perceptions of vulnerability and their involvement in NBS strategies in the Ebro delta, Spain. The findings revealed that there is consensus on the socio-economic issues that climate risks can cause in the delta, as well as the absence of adaptation methods. There is a clear need for a strong commitment by local, regional, and national governments, as well as stakeholders, to build a new type of collaborative governance that has not previously been achievable.

Moreover, another empirical research was carried out in the coastal region of the Inner Forth estuary in Scotland by [97]. They investigated the role of controlled re-alignment, a natural-based coastal adaptation technique that permits farmland to be converted to wetlands. While farmers backed seawalls, local inhabitants primarily preferred managed re-alignment, according to interviews conducted with 16 organizations and 109 citizens living in the Inner Forth estuary zone. Local adaptive capacities are hampered by a lack of stakeholder and citizen participation, according to the findings.

Ref. [98] argued that there is a gap between the information produced by scientists and the information needed by stakeholders. Their paper addressed this gap through empirical research in the Biebrza Valley in Poland. This research was important for this region, as the frequency of floods has increased dramatically in the area. It was found that increased stakeholder engagement can ensure effective adaptation to floods. The research challenges were: simple communication of climate science to construct effective policies; accounting for uncertainty as part of adaptation plans; environmental project monitoring.

To add to this, ref. [9] developed an innovative NBS assessment framework using fuzzy cognitive mapping (FCM). A case study from the Lower Danube region (Romania) was used, as part of the EU NAIAD project. Individual FCMs were created using semi-structured interviews to collect information about water-related dangers. Stakeholders were asked to state what they expected from NBS in terms of decreasing water-related risks and resolving societal issues. Ultimately, this work successfully demonstrated that differences in co-benefits perception led to trade-offs amongst stakeholders. Another EU NAIAD publication by [99] assessed the role of stakeholder engagement in implementing NBS for flood risk reduction using the case of Ljubljana, Slovenia. This research created a Systems Dynamic Model to quantitatively examine the effectiveness of NBS. In order to motivate stakeholders, ref. [99] claimed that NBS’s multi-functionality and monitoring its co-benefits have become important to NBS programs. Ref. [100] developed a framework incorporating the maturity model to study the involvement of stakeholders in the city-building process as part of the EU European Smart Mature Resilience Project. They created a model using an iterative process that involved conducting interviews in Bristol and Glasgow in the United Kingdom, San Sebastian in Spain, Rome in Italy, Vejle in Denmark, and Kristiansand in Norway.

Ref. [101] studied the role of stakeholder engagement in coastal zone management. A variety of conflicting perspectives exist on coastal zone management in the context of climate change, and it is important to incorporate these complexities for long-term coastal planning. Research exists that describes management actions for the coast [102,103,104,105] and the use of stakeholder preferences in selecting options [106,107,108,109] yet little research exists on how climate change can be incorporated into decision-making processes. In this context, they were the first ones to suggest a novel method scenario-based stakeholder management to manage coastal areas in the UK in the context of climate change. Tompkins et al. (2008) found that scenario-based stakeholder engagement should be introduced as part of Shoreline Management Plans in the UK, for better coastal management.

To conclude, there are a plethora of studies studying the relationship between NBS and stakeholder engagement from varied vantage points. Whist [20,65] make use of systematic reviews to study the role of public perceptions for the implementation of NBS and the role of stakeholders in NBS co-benefits and trade-offs identification, refs. [96,97,98,101] conducted empirical research in diverse European coastal settings, including Scotland, Spain, and Poland. In addition to this, ref. [99] developed a framework for studying stakeholder engagement as part of the EU NAIAD project, and [100] as part of the EU European Smart Mature Resilience project. Although each study presents unique findings, all of them indicate that stakeholder participation plays a crucial role in the implementation and success of NBS initiatives.

4. Discussion

4.1. Role of Living Labs in Climate Adaptation through NBS

CCLLs are based on the aforementioned LL concept but focus on co-developing coastal city interventions and activities through novel EBAs. CCLLs aim to tackle specific coastal challenges, including erosion, flooding, storms and sea-level rise.

Although the interlinkages between LL and climate adaptation have not yet been studied effectively, through the analysis conducted as part of this review, it can be ascertained that climate adaptation and LL are inextricably linked (Zoelch et al., 2018). This is because: (i) LLs have demonstrated potential to address various barriers to NBS adoption for climate adaptation (e.g., a lack of dialogue and support, limited knowledge, low attention in the planning system, and so on); (ii) LLs are based on the concept of ‘collaborative governance, which can be extremely effective for climate adaptation through adoption of NBS schemes (Wamsler, 2016); (iii) LLs have aided in effective decision-making the face of climate uncertainty, as they can bring together diverse stakeholders and interdisciplinary techniques (Huang-Lachmann, 2019); (iv) LLs have served as standards for scaling-up NBS for dealing with climate-related natural disasters because they promote a user-centric approach in which information and skills can be efficiently shared (Kumar et al., 2021); (v) there has been a considerable demand for local support for NBS schemes, which is exactly what LLs can provide (Zoelch et al., 2018); and (vi) LLs encourage citizens and stakeholders to be proactively involved in the process of designing and implementing innovative schemes, which can also assist with effective climate adaptation (Chroneer et al., 2019).

4.2. Role of NBS in Building Coastal Resilience

This review article established that coastal flood mitigation is one of the key motivations for implementing NBS, and its popularity has been growing due to its effectiveness and resilience in the face of storms and floods (Hanson et al., 2020). This holds true especially for urban coastal areas (e.g., [110,111,112,113,114,115]). Numerous studies indicated the relatively lower costs and flexibility of NBS compared to hard-engineering-based measures are contributing to their popularity (Brink et al., 2016).

Whilst the use of NBS for coastal mitigation is rapidly increasing around the globe, their success depended on numerous factors and their effects are still difficult to monitor. In this context, the frameworks and strategies developed by [40], Sarabi et al. (2020), [23,24,25] have proven to be particularly effective for coastal NBS implementation. These studies and their findings further reinforced NBS’ growing role in coastal flood mitigation and its potential for coastal DRR.

4.3. Socio-Economic Welfare in the Context of NBS Implementation

This review article has found that although more publications are recognizing the importance of socio-economic co-benefits for the success of NBS projects, most of these projects still focused primarily on environmental agendas. One of the reasons for this is that it has not always been easy to quantify and address socio-economic concerns [76]. The relationship between EBA/NBS and socio-economic welfare is multi-layered, complex and non-linear.

This review article has established the importance of considering socio-economic indicators in order to successfully implement NBS schemes for urban flood risk management. People’s geographical location, education levels, income levels as well as cultural upbringing determine their perceptions of NBS [17]. Whilst NBS can be affected by people’s perception, it can also act as an inclusive mechanism to address the challenges faced by marginalized groups much more effectively than engineering-based alternatives [84]. EBA is specifically suitable for this purpose due to the high dependence of these groups on the local ecology for their livelihoods [84]. EBA can have multiple benefits for social empowerment [78]. EBA and NBS both also have multiple co-benefits, many of which are socio-economic in nature [85,86].

Finally, several authors have developed frameworks to assess the potential of NBS for socio-economic well-being. For instance, ref. [74] developed the FRASH framework; ref. [75] developed a framework to address socio-economic vulnerability in coastal areas; and ref. [28] created a framework to appraise the socio-economic effect of floods in the EU.

4.4. Stakeholder Engagement in the Context of NBS Implementation

Although each study presents unique findings, overall, this review article has established that stakeholder participation is crucial for the success of NBS initiatives [65]. However, stakeholder engagement has been a complex and challenging task due to the diverse nature of the participants involved. Although public engagement is a common goal of NBS projects, the engagement processes are rarely based on a thorough understanding of the factors influencing public perceptions [68]. In addition to this, there has been a gap between the information produced by climate science and the information needed by stakeholders, which can sometimes hamper effective NBS implementation [98].

Finally, several authors have developed frameworks to incorporate stakeholders in NBS implementation schemes. For example, ref. [9] developed an FCM-based framework to assess NBS effectiveness amongst stakeholders; ref. [99] assessed the role of stakeholder engagement in implementing NBS for flood risk reduction; ref. [32] developed a value-based framework to facilitate stakeholder engagement in NBS planning; and ref. [101] developed scenario-based stakeholder management to manage coastal areas in the UK.

4.5. Synergies between NBS, Disaster Risk Reduction and Living Labs

Although the concepts of LL, DRR and NBS originate in diverse scientific disciplines, there are significant overlaps when they are studied in collaboration for the sustainable management of natural disasters. As has been discussed earlier, the concepts of DRR, LL and NBS all require stakeholder engagement for their successful implementation. NBS and DRR initiatives usually also have socio-economic co-benefits, even if their main goal is climate adaptation. All three concepts usually succeed through a collaborative form of governance and co-production of knowledge. Figure 9 illustrates the overlaps between LL and NBS; NBS and DRR; and DRR and LL, respectively; and also illustrates the synergies between LL-NBS-DRR together.

4.6. Research Gaps and Future Prospects

This review article studied interlinkages between a range of concepts, including NBS, EBA, LL, DRR, stakeholder engagement, socio-economic impacts, coastal resilience, and more. Whilst this study addresses pertinent research gaps, the systematic nature of the analysis has also highlighted some additional research gaps as well as future research prospects, as part of

Table 4. Research Gaps and Future Prospects.

Subject Matter	Number of Publications	Knowledge Gaps	Future Research Prospects
Linkages between NBS and LLs	8	Synergies and trade-offs between NBS and LLs	-Defining how LLs can support NBS implementation -Defining how NBS can support the LL co-creation process better than traditional infrastructure
Relationship between NBS and EBA	7	Synergies and trade-offs between NBS and EBA	-SDGs achieved by NBS and EBAs
Role of NBS for DRR	21	Framework for selection of appropriate NBSs for different disasters	-Defining the role of NBS for DRR -Exploring socio-economic vulnerability in the context of NBS for DRR -Involving stakeholders in the management of natural hazards
Relationship between LL and DRR	3	Synergies and trade-offs between LL and DRR	-Defining how LLs can complement DRR schemes
Hybrid NBS	6	Role of NBS compared to traditional engineering-based infrastructure	-Cost effectiveness of NBS versus traditional infrastructure -Longevity and resilience of NBS versus traditional infrastructure -Effectiveness of Hybrid infrastructure versus engineering-based infrastructure
Linkages between NBS/EBA and stakeholder engagement	14	Role of stakeholder participation in successful Implementation of NBS	-Incorporating stakeholders in the implementation of NBS
Linkages between NBS/EBA and socio-economic conditions	7	Direct and indirect effects of NBS schemes on socio-economic conditions	-Measuring socio-economic co-benefits of NBS -Measuring socio-economic vulnerability as part of NBS schemes

.

5. Conclusions

This article has presented a systematic review that offers insights into concepts such as NBS, EBA, DRR, LL, stakeholder engagement and more in the context of coastal urban adaptation. The article studied the linkages between the aforementioned concepts, bridging them together to offer a new, interdisciplinary approach towards coastal risk reduction. This review has focused exclusively on the European context, which as has been indicated earlier, is an ideal setting for NBS and LL-related research. This paper also draws attention to the coastal regions within Europe and specifically addresses challenges such as coastal floods, storms, erosion and sea-level rise- some of the most potent natural threats today. The CCLL concept has been created as part of the EU SCORE project to establish ‘living laboratories’ in European coastal cities, as these will be affected by the increase in frequency and intensity of natural hazards, owing to the ongoing climate crisis. This review paper has studied the role of fresh and upcoming concepts such as LL and NBS/EBA in order to combat these natural disasters.

This article has found EBA and NBS, specifically hybrid NBS to be a resilient, flexible and cost-effective approach for mitigating floods and coastal storms. Numerous authors demonstrated the potential of LL for the implementation of successful NBS schemes. This is due to LL’s ability to aid decision-making in the face of climate uncertainty; LL’s use of collaborative governance which aids adaptation; and LL’s potential to address adaptation barriers. Multiple studies have also indicated the importance of stakeholder engagement for both NBS as well as LL implementation. The LL model has clearly defined stakeholders (such as academia, government, private sector and civil society), which can be useful for managing stakeholder engagement processes within NBS initiatives. Studies also demonstrate the crucial role stakeholder engagement plays in NBS implementation for climate adaptation. Negative perceptions of stakeholders can severely hamper the success of NBS-LL projects, and lead to failure. In order to achieve the goal of DRR, numerous authors have developed frameworks for achieving effective stakeholder engagement as part of NBS schemes.

This article found that it is critical to include a socio-economic analysis of costs and benefits to effectively implement NBS projects. Socio-economic factors such as education, income levels, environmental attitudes and more, significantly affect the success of NBS-LL-DRR schemes. The papers demonstrate that EBA/NBS schemes can aid with social empowerment and also assess socio-economic vulnerability as part of NBS-DRR schemes. This article also found synergies between LL, NBS and DRR, including: (i) the LL model allows replicability of the NBS-DRR initiatives in the long term; (ii) the co-production of knowledge in the NBS-LL-DRR schemes links ecosystem services with science and (iii) the LL model increases trust in local governance, which aids NBS-DRR initiatives. The main challenge to the implementation of these new-age NBS-LL-DRR schemes is the lack of research as well as a limited understanding of the synergies and trade-offs between these concepts. Finally, this paper also helps define additional research gaps, relating to the linkages between NBS and LL; the linkages between NBS and DRR; hybrid NBS; the relationship between EBA and NBS; and further research possibilities relating to these gaps.

Although these concepts originate in diverse scientific and academic disciplines, a study of their interlinkages provides innovative tools for effective climate adaptation. For example, the living lab can be an effective means of engaging citizens in climate action, which has been an under-researched theme. Another example is the growing recognition of including socio-economic well-being in climate adaptation policies and the role of EBA in aiding this process. Yet another example is the ability for DRR strategies to overlap with climate adaptation goals, through tools such as NBS and LL. These examples demonstrate the potential of, and offer key insights in, interdisciplinary and transdisciplinary climate adaptation strategies.