Strategies for mainstreaming nature-based solutions in urban governance capacities in ten European cities

The paper addresses how to overcome the implementation gap in nature-based solutions (NBS) by mainstreaming them within urban governance. Despite widespread advocacy and documented environmental, social, and economic co-benefits, NBS implementation often remains limited to isolated pilots with insufficient long-term management. Institutional, organizational, and cultural barriers in city governments—such as siloed departments, rigid funding prioritizing cost over socio-ecological value, and limited public engagement—hinder scaling. The study seeks to clarify what mainstreaming entails and how it can be realized through institutional changes in planning tools, routines, and governance settings. It adopts the lens of institutional mainstreaming as an incremental, iterative process of experimenting with and reforming governance rules, relations, practices, and discourses to build capacities for coordination, integration, and inclusion. The research explores how city officials in ten European cities, through the Connecting Nature project, experimented with novel governance processes and mechanisms across the NBS lifecycle to develop capacities for systemic, inclusive, and reflexive planning, delivery, and stewardship.

Prior research highlights NBS co-benefits for addressing multiple urban sustainability challenges and resilience, but identifies persistent implementation barriers including sectoral silos, financing models emphasizing narrow cost-effectiveness, and limited public inclusion. Emerging scholarship argues mainstreaming requires shifting institutional structures and routines rather than merely integrating NBS into existing policy domains. Demonstration projects underscore institutional learning and the role of planners as institutional entrepreneurs in adapting instruments, regulations, and collaborative practices. Gaps remain in systematically investigating how to operationalize mainstreaming processes, build cross-sectoral capacities, and embed co-creative and reflexive practices. The paper builds on work on policy mainstreaming, adaptive and collaborative governance, and reflexive monitoring to propose process-oriented strategies and stepping stones that change governance conditions (rules, relations, practices, discourses) necessary for scaling NBS.

Design: Qualitative comparative case study of ten European cities within the EU Horizon 2020 Connecting Nature project (June 2017–June 2021). The three frontrunner cities (Genk, Glasgow, Poznań) and seven fast-follower cities (A Coruña, Burgas, Ioannina, Málaga, Nicosia, Pavlos Melas, Sarajevo) applied the Connecting Nature Framework across NBS planning, delivery, and stewardship. Approach: Inter- and transdisciplinary knowledge co-production combined with reflexive monitoring in an iterative peer-learning process. Activities included workshops, webinars, interviews, field visits, city-to-city mentoring, and knowledge hub sessions. Cities were equal partners, co-leading research and innovation. Data sources: Continuous documentation of city activities and governance innovations; monthly/bi-monthly reflexive monitoring sessions (especially with frontrunners); city reports on framework application; supplementary materials on governance innovations and strategy implementation. Analysis: Inductive, three-step comparative analysis conducted iteratively with partners: (1) clustering all city interventions across the NBS lifecycle into three emergent mainstreaming strategies reflecting governance capacities (systemic, inclusive, reflexive); (2) identifying ‘stepping stones’—key interventions overcoming governance inertia; (3) characterizing changes in governance conditions (rules, relations, practices, discourses) created or mobilized. Ethics complied with relevant regulations.

• Three mainstreaming strategies emerged that institutionalize governance capacities:
  1. Institutionalizing a systems' approach to NBS: linking NBS to cross-cutting policies and SDGs; embedding in regulatory frameworks; formalizing cross-departmental relations and roles; integrating skills (e.g., ‘green agents’); developing NBS-aligned business models (adapted Business Model Canvas) to diversify financing; positioning NBS as priorities within climate and regeneration agendas.
  2. Institutionalizing inclusive collaboration: building co-production capacity (staffing, tools, skills); tailoring engagement to goals and audiences; establishing informal and formal platforms for ongoing participation; formalizing collaborative governance models and hybrid financing; strengthening community empowerment and self-management (training, information points, shared spaces).
  3. Institutionalizing reflexivity and continuous learning: adopting reflexive monitoring to identify critical turning points and adapt in real time; developing impact assessment strategies with context-specific indicators across environmental, social, economic, and governance dimensions; creating partnerships and platforms for data sharing and learning (e.g., Urban Observatory; citizen science integrated into strategies).
• Concrete examples across the ten cities include: legally binding strategies and action programs (Glasgow OSS); inclusion of NBS in municipal development plans (Burgas); cross-departmental working groups (Genk); replication of nature-oriented playgrounds via cross-departmental ‘green agents’ (Poznań); collaborative financing and governance models with pre-schools (Poznań); community-managed urban gardens with training and revised tenders (A Coruña); CSR-linked engagement and ‘Adopt-a-Park’ schemes (Nicosia); NBE support and accelerator programs (Glasgow, A Coruña, Poznań); regular reflexive monitoring meetings (Ioannina, Genk); citizen science feeding into strategic planning (Glasgow).
• Outcomes include changed governance conditions: new rules (formal roles, procedures, funding mechanisms), relations (cross-departmental and public–private collaborations), practices (dedicated positions, routine co-production and reflexive monitoring), and discourses (place-based narratives of co-benefits and regeneration).

The findings demonstrate how NBS, as systemic innovations, can catalyze institutional learning and change by empowering policy officers as institutional entrepreneurs to rework governance rules, relations, practices, and discourses. Mainstreaming progressed where cities embedded cross-sectoral alignment, co-production, and reflexive learning into organizational procedures, staffing, and financing mechanisms. Differences across cities reflect varying entry points (strategic city-wide versus replication of small-scale interventions) and governance contexts, yet all advanced towards capacities for systemic, inclusive, and reflexive NBS. Frontrunner cities extended governance innovations to other urban agendas (e.g., energy, mobility), indicating broader governance shifts. Persistent barriers—such as inconsistent political support, short-term financing and procurement emphasizing costs over benefits, departmental silos, and limited capacity to engage diverse communities—constrain scaling. Evidence generation (impact assessment, reflexive monitoring) and peer learning facilitated cross-departmental buy-in and adaptation, but large-scale private financing remains challenging without higher-level policy and market changes. Transferability may benefit from capacity-building programs (e.g., UrbanByNature) and sustained city-to-city exchange.

This study contributes a process-based understanding of institutional mainstreaming of NBS, articulating three actionable strategies with associated stepping stones and governance condition changes that build capacities for systemic integration, inclusive collaboration, and reflexive learning. By documenting how city teams operationalized tools (e.g., Business Model Canvas, citizen science, reflexive monitoring) and embedded new roles and procedures, the work moves beyond barrier identification to show how to create enabling governance conditions. Future research and practice should: (1) support multi-level policy reforms to align financing and procurement with NBS co-benefits; (2) strengthen evidence on the value of co-production and cross-departmental collaboration; (3) enhance methods to engage diverse and underserved communities; (4) scale capacity-building and peer-learning platforms to transfer frameworks and practices; and (5) further institutionalize reflexive learning in decision-making cycles and urban observatories for continuous adaptation.

• Many barriers lie beyond city teams’ control: inconsistent political support, short-term financing and procurement rules prioritizing costs, and limited organizational staffing.
• Departmental silos and institutional hierarchies remained difficult to overcome despite progress with working groups and collaborative models.
• Large-scale private-sector financing was not unlocked; enabling market conditions require national/EU-level intervention.
• Persistent challenges in engaging diverse residents, especially immigrants and low-income groups.
• Extensive inter- and transdisciplinary support within the project may limit straightforward transferability to cities without similar resources.
• The approach emphasizes process learning and institutional change rather than ex-post quantitative impact attribution.