Mainstreaming NbS for Water Resilience: A Process-Oriented Framework and Evidence from European Regions (EU HORIZON Project NBRACER)

Environmental challenges such as floods, heatwaves, and droughts and ongoing biodiversity loss are intensifying under climate change, thereby increasing the interest in Nature-based Solutions (NbS) as measures for mitigation and adaptation. Advancing NbS beyond pilot sites requires their systematic integration into policies, planning, and development practices, a process commonly referred to as mainstreaming. NbS mainstreaming is constrained by institutional, organisational, and cultural barriers, as well as development pathways historically dominated by technological and grey infrastructure solutions. While existing research has documented where and why mainstreaming occurs, less attention has been paid to how it unfolds as a dynamic process of change. Conceptualising mainstreaming as a process of innovation adoption and social learning, encompassing integration, institutionalisation, policy uptake, and governance transformation, is therefore critical to enable the systemic changes needed to embed NbS as standard practice in water and climate resilience planning.

The study employed a mixed qualitative approach to develop and refine a framework for mainstreaming NbS. Existing literature and prior project outputs on mainstreaming were systematically reviewed and compiled into a structured database to capture types of mainstreaming activities and associated capacities. A selected analytical framework was used to guide the design of interview protocols and data collection across regions. Empirical evidence was gathered through structured surveys, semi-structured interviews, and cross-regional knowledge exchange activities, including webinars, to identify best practices and facilitate peer learning. Case study insights were iteratively analysed to refine and expand the framework, in alignment with NBRACER’s work on transformational governance. Mainstreaming practices were documented by mapping regional experiences against established typologies, with additional elements incorporated where empirical evidence revealed gaps. This iterative process resulted in a living, practice-oriented framework that evolves as new forms of mainstreaming emerge.

The methodology is illustrated through a set of water-related NbS case studies representing diverse governance and biophysical contexts. These include the SIGMA Plan in Flanders, exemplifying a shift from engineered flood control to floodplain restoration; the Klimatorium initiative in Denmark, which facilitates cross-sectoral collaboration for climate-resilient water solutions; the Water-and-Soil Guiding Principles in Friesland (Netherlands), embedding NbS within regulatory planning frameworks; rainwater harvesting and constructed wetland systems in East and West Flanders; wetland restoration initiatives in Nouvelle-Aquitaine (France); and the interceptor channel in Cávado, Portugal, integrating flood protection, ecosystem restoration, and recreational functions.

Cross-case analysis identifies key enabling conditions for NbS mainstreaming, including the role of extreme events as catalysts for change, the importance of regulatory alignment and long-term policy commitment, and the influence of knowledge brokers and institutional champions. Social learning plays a central role. Co-design processes, trust-building, and iterative feedback loops enabled stakeholders to shift from scepticism to ownership. The findings further highlight the value of incremental implementation pathways, robust monitoring and evaluation frameworks, and comparative assessment methods that account for NbS co-benefits relative to conventional grey infrastructure.

These results underscore the importance of integrated social, institutional, and technical strategies for scaling and embedding NbS in governance and planning systems.