Source-linked AI summary
Nature-based solutions in the urban context: terminology, classification and scoring for urban challenges and ecosystem services
Joana. A. C. Castellar, Lucia . A. Popartan, Josep Pueyo-Ros, Natasa Atanasova, Gunter Langergraber, Ina Saumel, Lluis Corominas, Joaquim Comas, Vicenc Acuna
TL;DR
The paper addresses persistent disagreement over NBS definitions, terminology, classification, and assessment in terms of urban challenges and ecosystem services. It integrates knowledge from four European projects using mixed quantitative-qualitative methods to develop a common framework. The resulting framework provides 32 evaluated NBS, a novel classification scheme, and evidence of uneven agreement across performance domains and identification criteria.
Problem
Disagreement over NBS definitions, terminology, classification, and UC and ES assessment makes the concept difficult to delimit consistently.
Method
The study integrates four European projects through workshops, surveys, expert interviews, statistics, and qualitative UC and ES evaluations.
Results
The paper delivers 32 NBS with UC and ES evaluations and a novel classification scheme, while finding stronger agreement for environmental UC and some ES than for socio-economic UC and supporting and provisioning ES.
Takeaways & Limitations
The framework contributes to a common understanding of NBS and identifies the ‘green factor’ and non-intensive nature-based practices as key practitioner criteria.
Takeaways & Limitations
The assessment requires further research coupling cognitive analysis with other qualitative methods, and missing UC assessments can bias results.
Abstract
from arXiv · showhide
The concept of Nature-Based Solutions (NBS) has emerged to foster sustainable development by transversally addressing social, economic, and environmental urban challenges. However, there is still a considerable lack of agreement on the conceptualization of NBS, especially concerning typologies, nomenclature, and performance assessments in terms of ecosystem services (ES) and urban challenges (UC). Therefore, this article consolidates the knowledge from 4 European projects to set a path for a common understanding of NBS and thus, facilitate their mainstreaming.
Graphical abstract 18
The study integrates NBS knowledge from four European projects into a common list, classification, terminology, and assessment framework. It distinguishes NBS units from NBS interventions and finds differences in versatility and assessed performance across urban challenges and ecosystem services.
- Approach: The methodology combined workshops, web-based surveys, hierarchical clustering, qualitative project scores, PCA, and an evenness index.These steps supported terminology, classification, and integrative performance assessment.
- Classification: The resulting framework provides a list of 32 NBS and introduces NBS units and NBS interventions as distinct categories.NBS units are stand-alone green technologies or urban green spaces; NBS interventions involve intervening in existing ecosystems or NBS units.
- Performance: NBS units are 35 more versatile than NBS interventions in terms of urban challenges and ecosystem services.The statistical analysis reports this difference between the two categories.
- Performance: Performance assessments show greater agreement for environmental urban challenges and cultural and regulating ecosystem services than for socio-economic challenges and supporting and provisioning services.The comparison concerns agreement across the integrated project assessments.
- Identification: The ‘green factor’ and replication of non-intensive practices occurring in nature are key criteria practitioners use to identify an NBS.These criteria emerge from the reported practitioner-oriented assessment.
1. Introduction
NBS has gained broad uptake, but inconsistent definitions, terminology, classification, and performance assessment leave the concept difficult to delimit. The paper addresses this gap by integrating knowledge from four European projects through a mixed quantitative-qualitative methodology.
- Context: NBS is associated with sustainable, resilient, socially inclusive cities and with addressing economic, environmental, and social urban challenges.Definitions emphasize different aspects, including sustainability pillars and conservation or restoration actions.
- Conceptual gap: Multiple definitions and disagreement over NBS characteristics have created confusion about what does and does not qualify as an NBS.The concept overlaps with established environmental approaches such as ecological engineering and green infrastructure.
- Conceptual gap: Different projects classify and assess NBS inconsistently, particularly regarding urban challenges and ecosystem services.This problem is especially evident across projects funded under the European Horizon 2020 program.
- Terminology: The same solution may receive different names, including “green façade with climbing plants,” “climber green wall,” “ground-based greening,” or “green façade.”The examples illustrate the lack of agreement over NBS terminology.
- Objectives: The paper aims to establish common NBS typologies, terminology, classification, and evaluation by integrating knowledge across four H2020 European projects.Its mixed methodology uses workshops, expert interviews, surveys, statistics, and qualitative project evaluations.
- Objectives: The stated objectives include a practitioner-preferred nomenclature, a user-friendly classification, conceptual criteria for identifying NBS, and an integrative UC and ES assessment.Together, these objectives target communication, knowledge-sharing, conceptualization, mainstreaming, and performance overview.
2. Methods
The study used three linked stages: constructing a shared NBS list, reaching consensus on terminology and classification, and integrating UC and ES assessments from H2020 projects. It also applied statistical analyses while acknowledging missing-value constraints.
- Study design: Researchers developed a common NBS list across H2020 projects, built terminology and classification consensus through worldwide surveys, and integrated UC and ES scores statistically.The three stages covered list development, consensus-building, and performance assessment.
- NBS list: Experts consolidated similar NBS across projects using shared roles of nature, technical or design requirements, implementation scale, and benefits.Only NBS considered similar or equal across at least two projects were selected for robustness and cross-source assessment data.
- Study design: The project review selected NBS projects that provided classification or nomenclature and assessed urban challenges or ecosystem services.The review covered URBANGREENUP, UNALAB, NATURE4CITIES, and THINKNATURE.
- Terminology: Two surveys elicited preferred NBS names, using a 50% voting threshold and follow-up statistical testing when no name reached that threshold.Where preference remained unclear, Scopus publication counts and expert consultation helped determine final names.
- Classification: The proposed classification has three hierarchical levels and begins with three intervention types ranging from minimal ecosystem intervention to intrusive management or ecosystem creation.The first level draws on Eggermont et al.’s categories, while later levels use expert interviews and literature scanning.
- Assessment: The integrative assessment calculated crossed UC and ES scores, normalized individual NBS scores, and applied multivariate analysis including PCA and an evenness index.The assessment combined score calculation, visualization, and multivariate analysis.
- Assessment: Urban challenges with more than one missing assessment value were excluded to reduce bias from missing data.This exclusion constrained the assessment of incompletely evaluated urban challenges.
3. Results
The study consolidated NBS from four European projects into a common list, terminology, hierarchical classification, and integrative assessment of urban challenges and ecosystem services.
- 3.1 Common list of NBS: The selection process excluded 62 items because they were not considered NBS, including nature-inspired but non-natural interventions and overly intensive practices.Examples included permeable concrete and small-scale urban livestock.
- 3.1 Common list of NBS: A further 33 NBS were excluded because they were not similar or equal across at least two projects, with design and implementation scale more relevant than benefits for judging similarity.
- 3.1 Common list of NBS: Expert elicitation produced a common list of 32 NBS representing 107 NBS from four H2020 projects.
- 3.2 NBS common terminology and classification: The 32 common NBS were organized into a three-level hierarchy distinguishing NBS units from interventions, then differentiating units by spatial or technological form and interventions by purpose or site.The third level groups spatial units by vegetation form and technological units by implementation scale.
- 3.3 Integrative assessment framework for urban challenges and ecosystem services: The PCA’s first two dimensions explained 49.4% of model variance and showed no obvious NBS clustering, although the proposed categories generally performed properly across the two dimensions.Spatial units scored well on social issues, climate resilience, and air quality, while most interventions performed well for provisioning and supporting ecosystem services.
4 Discussion
The discussion refines what counts as a Nature-Based Solution, proposes terminology and classification advances, and evaluates NBS performance across urban challenges and ecosystem services. Results show stronger agreement for environmental challenges and regulating and cultural services, while the green-factor criterion excludes some nature-based filtration solutions.
- Defining NBS: Participants treated vegetation—the paper’s “green factor”—as central to NBS, while replication of natural processes alone was necessary but insufficient.Porous asphalt replicated water infiltration but did not require the green factor.
- Defining NBS: Participants also associated NBS with non-intensive resource use and occurrence in nature, excluding solutions judged artificial or resource-intensive.The discussion excludes smart soil production and small-scale urban livestock under these criteria.
- Defining NBS: Requiring greenness excludes natural filtration solutions such as infiltration trenches, despite their use of natural, non-intensive filtration processes.This criterion therefore removes some elements based on biofiltration through natural porous material.
- Defining NBS: The discussion identifies resistance to planning and management approaches as NBS, although these approaches are presented as supportive for maintaining natural capital and implementing and monitoring NBS.The literature is cited as validating the participants’ exclusion of these approaches from the NBS category.
- Standardization: The paper proposes a compact hierarchical NBS classification and a formalized terminology list that identifies a cross-project core and supports future standardization.The classification is described as robust because categories align with addressed urban challenges and delivered ecosystem services.
- Integrative assessment: Performance assessment showed higher agreement for environmental challenges and regulating and cultural services than for socio-economic challenges and supporting and provisioning services.Green space management scored highest among urban challenges, while participatory planning scored lowest; regulation and cultural services also exceeded supporting and provisioning services.
- Integrative assessment: The multivariate analysis found more co-benefits for NBSsu than NBStu and NBSi, with no overlap in NBS applications across urban challenges and ecosystem services.The authors interpret the alignment between classification and performance dimensions as evidence of classification robustness, and provide an online scoring tool.
5 Conclusions
The article consolidates diverse NBS knowledge into a common terminology, classification, and assessment framework, while showing that the proposed scheme remains open to refinement. It argues that shared language and holistic understanding can support knowledge transfer, replication, and more resilient cities.
- The study delivers a replicable methodology and a set of 32 NBS evaluated for Urban Challenges and Ecosystem Services.
- Its novel classification scheme is designed for systematic knowledge representation, open expansion, and integration of databases beyond the four analysed H2020 projects.
- NBS are conceptualized as components of larger living systems whose interactions with other nature-based or grey solutions can diversify ecosystem services, close resource loops, and compensate disservices.
- Practitioners associate NBS particularly with a green factor and non-intensive resource use, insights that can inform clearer and more comprehensive definitions.
- The proposed list, terminology, and classification are not definitive; further research should distinguish NBS interventions from other green planning approaches and review excluded solutions.
- The integrative assessment indicates that evaluation efforts should especially address socio-economic challenges and supporting and provisioning services for technological and interventional NBS.
MOTIVE
The paper motivates a common NBS framework by addressing inconsistent classifications and a lack of performance assessment for urban challenges and ecosystem services. It distinguishes NBS from related but non-equivalent approaches, technologies, benefits, and planning tools.
- A lack of performance assessment in terms of urban challenges and ecosystem services motivates the integrative framework.
- The framework separates NBS from measures inspired by nature but not employing nature, benefits dependent on plant selection, and approaches that are too intensive.
- Some entries are classified as typologies of NBS or as planning approaches and tools supporting NBS implementation or ecosystem preservation and monitoring.
- The reviewed material spans diverse NBS, including green roofs, urban green spaces, wetlands, river restoration, permeable pavements, and habitat measures.