The term NbS first emerged on the global stage during the UNFCCC negotiations in 2009 and has since increasingly gained attention. NbS covers a wide range of practices including for example integrated water resource management, forest landscape restoration, ecosystem-based adaptation and mitigation, and ecosystem-based disaster risk reduction. A widely used definition of NbS is that they are actions to protect, sustainable manage and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits. Solutions often enhance existing natural or man-made infrastructure and spur long-term economic, social and environmental benefits.

NbS that contribute to water security can vary widely and have multiple benefits. They can improve water availability and water quality, whilst simultaneously reducing water-related risks and generating additional social, economic and environmental co-benefits. Examples of the types of water-related NbS include: source water protection; wetlands restoration, protection, and construction; water harvesting; agricultural best management practices; soil conservation; afforestation; protecting mangroves

The terminology ‘green infrastructure’ is also often used in relation to NbS, and is a subset of NbS. Green infrastructure for water refers to the natural or semi-natural systems that provide water resources management options with benefits that are equivalent or similar to conventional grey (built/physical) water infrastructure (World Water Development Report, 2018).

Challenges for the planning and implementation of NbS include (adapted from the World Water Development Report 2018):

1. Dominance of grey-infrastructure solutions: Existing governance systems, including management instruments, orientation of economic markets, expertise of service providers, and policy makers have been dominated by an grey infrastructure mentality.
2. Institutional fragmentation and sectoralised forms of decision making that hinder the uptake of NbS (which are intrinsically inter-sectoral) leading to a default back to grey infrastructure as a solution.
3. Regulatory and policy barriers: for example, investments made in NbS or green infrastructure cannot, under certain national frameworks, be counted today as ‘capital expenditure’ by investors in the same way as grey infrastructure.
4. Inadequate financial models: limiting potential investments towards NbS.
5. Important capacity & knowledge limitations: A lack of awareness, communication and knowledge of what NbS can really offer to enhance water security. An overall lack of capacity to implement NbS in the context of water, with nascent and scattered expertise, and lack of standardization of NbS approaches.
6. Potentially large physical footprint: NbS such as conservation of forests, restored wetlands or extensive farming can have significant land requirements.

Some of the key elements for creating an enabling environment and integrating NbS into national planning are listed below; bearing in mind that the implementation of NbS measures takes place at the landscape level and many of these points will be applicable to planning for NbS at lower scales. These have been aggregated from a selection of sources including the World Water Development Report (2018), Seddon (2018), and Seddon et al. (2021).

Institutional and regulatory environment

• Enhancing national and regional regulations and frameworks, including by assessing the legal and regulatory regimes in place, removing existing barriers to NbS uptake, developing enabling legislation and plans focused on NbS and identifying where and how NbS can support existing planning approaches at different levels.
• Leveraging international and global frameworks, as NbS offer countries a means to respond to and use various multilateral environmental agreements, such as the Convention on Biological Diversity, the UNFCCC and the Ramsar Convention on Wetlands
• Creating specific and measurable targets for nature-based solutions in national strategies such as the Nationally Determined Contributions.

Knowledge and capacity building

• Improving the knowledge base on NbS through evidence-based research and lessons learned
• Grounding NbS plans in science-based knowledge, as well as and local knowledge.
• Capacity development for practitioners to learn about NbS, develop NbS plans and approaches adapted to the socio-ecological context, mobilising financing for projects and providing technical support for project development, implementation and monitoring.

Working together

• Enhancing inter-sectoral collaboration and building coherence in national policy processes by bringing together policy makers and institutional actors from different sectors, scientists, and practitioners.
• Building on active cooperation with and between stakeholders
• Managing and implementing NbS projects by, or in partnership with, local communities with consideration of their rights and knowledge, supporting local livelihoods and reducing environmental vulnerabilities.

Mixing grey and green infrastructures

• Building on existing polices, by implementing grey and green infrastructure in an integrated manner. Example of such integration in water management can be seen in Table 1 below.

Table 1. Mixing Grey and Green Infrastructure. Adapted from Browder et al.  (2019).

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National governments, local authorities (Tool B1.02), basin organisations (Tool B3.04), businesses (Tool C5.05), donors and financial institutions, including development banks (Tool D2.04; Tool D2.05) are potential stakeholders in developing NbS projects. For a concrete NbS project to yield the outcomes desired, its design and verification should be based on a robust framework represented by the following criteria and corresponding indicators (IUCN, 2020): 

Criterion 1. NbS effectively address societal challenges: ensuring that a NbS is designed as a response to a challenge which was formulated during a participatory decision-making process, including community members. The following indicators to assess this are used: 

• The most pressing societal challenges are prioritised 
• The challenges are clearly understood and documented 
• Tangible and substantive benefits to human well-being are delivered. 

Criterion 2. Design of NbS is informed by scale: recognising the complexity and uncertainty coming from biophysical and geographical perspectives, as well as economic and political systems. The following indicators support the assessment: 

• NbS recognise and respond to interlinkages between the economy, society, and ecosystems 
• NbS seeks synergies across sectors 
• NbS incorporates risk analysis (Tool C1.01). 

Criterion 3. NbS result in a net gain to biodiversity and ecosystem integrity: avoiding undermining the integrity of an ecosystem. The following indicators shall demonstrate successful implementation: 

• NbS address drivers of degradation and loss 
• Biodiversity conservation outcomes are identified, benchmarked, and assesses 
• Potential negative externalities arising from the NbS are periodically assessed 
• Opportunities to enhance ecosystem integrity are incorporated into the NbS. 

Criterion 4. NbS are economically viable: considering economic viability of the project (Tool D1.01). The following indicators may be applied: 

• Direct and indirect benefits and costs are taken into account, together with identifying who pay and benefits 
• A cost-effectiveness study is conducted 
• Available alternative solutions are estimated 
• Various resourcing options, such as private and public sector, as well as voluntary commitments are considered. 

Criterion 5. NbS are based on inclusive, transparent, and empowering governance processes (Tool B1.05): NbS align with regulatory provisions, and mechanisms that engage affected stakeholders are activated. The following indicators will demonstrate that: 

• Feedback mechanisms are available 
• Participation is based on mutual respect and equality regardless of gender, age or social status (Tool B5.03) 
• Stakeholders affected are identified 
• Decision-making process responds to the rights of all participating stakeholders 
• Mechanisms to enable joint decision-making of the stakeholders in the affected jurisdictions are established. 

Criterion 6. NbS equitably balance trade-offs between achievement of their primary goals and the continued provision of multiple benefits: all the stakeholders should be consulted on how the trade-offs should be addressed. The following indicators may be used: 

• Costs and benefits of associated trade-offs are acknowledged 
• The rights and access to land and resources of different stakeholders are respected 
• Periodic revisions of mutually-agreed trade-offs limits are conducted. 

Criterion 7. NbS are managed adaptively, based on evidence: ensuring adaptive management to address uncertainty and harness ecosystem resilience. The following indicators are used: 

• NbS strategy is used as a basis for M&E 
• A M&E plan is developed 
• Iterative learning is applied to enable adaptive management. 

Criterion 8. NbS are sustainable and mainstreamed within an appropriate jurisdictional context: ensuring that NbS interventions aim at long-term sustainability aligning with sectoral, national and other policy frameworks. The following indicators help monitor that: 

• NbS design, implementation and lessons learnt are shared 
• NbS informs facilitating policy and regulation frameworks 
• NbS contributes to national and global targets for human well-being, climate change, biodiversity and human rights (Tool A2.05). 

Further detailed information on NbS implementation can be found on the following online platforms:    

• The Nature-Based Solutions Initiative has created a dynamic evidence platform for the consolidation of data on the effectiveness of NbS, as well as a policy platform which provides information on NbS in the Nationally Determined Contributions and scientific literature at the country level.   
• TNC Water Funds Toolbox provides guidance on a model approach to the protection of water sources, highlighting nature-based solutions and payment for ecosystem services (Tool D2.06).   
• ThinkNature Platform is an MSP supporting the understanding and promotion of NbS providing case studies, resources and a scenario game (Tool C2.03). 
• The REGREEN Nature Solutions Platform shares knowledge and experience on NbS, serves as online crowd-funding site and supports decision-making needed to implement NbS.