Problem statement
Cities worldwide are increasingly confronted with the impacts of climate change and an unparalleled decline in biodiversity. This has led to a growing interest in the use of Nature-Based Solutions (NBS), which are multi-purpose solutions, inspired and supported by nature, that aim to address societal challenges by protecting, sustainably managing, and restoring natural and modified ecosystems. Due to their multifaceted character, they are able to adapt to local needs and can simultaneously provide a range of social, environmental, and economic benefits. Although their potential and need have been acknowledged, their implementation in Dutch cities remains limited due to a deficient understanding of the factors that influence their adoption as well as the absence of guidance on how to overcome barriers, harness drivers, or implement strategies and measures that can support NBS uptake. Therefore, this research aims to address this knowledge gap by answering the following question:

“What are the factors influencing the implementation of NBS in Dutch cities, and how can these factors be integrated into a guiding implementation framework to support the adoption of NBS?”

Methodology
To answer this question, the design science research approach was employed. First, a review of grey and academic literature was conducted to analyze existing NBS frameworks used during the planning and implementation phases to derive insights into the characteristics such frameworks should possess. A second review identified the barriers and drivers influencing NBS adoption, the strategies and measures that can address these factors or generally facilitate implementation, and the principles that support sound practice. Based on these findings, hypotheses were formulated and explored through ten semi-structured interviews with experts, including both academics and practitioners. These interviews examined whether the factors identified in the literature also arise in practice within Dutch cities and helped contextualize their influence. Interviewees further provided requirements for the framework, complementing the literature-based findings. The interview data were analyzed using thematic analysis. Drawing on all collected insights, the Seeds of Change Framework was developed by synthesizing and visualizing the findings, resulting in a guiding implementation framework to support stakeholders in adopting NBS. Finally, the framework was applied to several illustrative cases to demonstrate its practical relevance and added value in facilitating NBS implementation.

Results – Framework requirements
Certain characteristics were identified to be recurrent in NBS frameworks. Most frameworks specify the framework’s type, nature, purpose, value, during which phase(s) of the urban planning process the framework should be used, and what the intended use and target user group are. For the framework’s application, some recommended a specific governance approach that can be followed. Content-wise, an important element found is the distinction between context, process/activities, and outcomes. For a barriers and drivers approach, organizing them into themes and assigning a relevance level to each factor can provide clarity and overview. Frameworks that included strategies or measures formulated these in the imperative form to communicate action while avoiding the assignment of responsibilities to specific parties. In addition, the text incorporated in the frameworks is formulated concisely. All frameworks are accompanied by supplementary material, often including expert commentary and real-life cases, to support practitioners in their application. Overall, the frameworks strived to achieve a balance between text and visual elements. Interviewees mentioned relatively similar elements. They underscored the importance of stating for whom the framework is intended and selecting a format that fits with these users by reasoning from a Theory of Change. Moreover, usability in terms of word choice, size, and required attention span was highlighted, implicating that sentences should be kept concise and that jargon should be avoided. It was also noted that summarizing the findings first could help keep the content manageable and maintain the reader’s focus on the most important elements, while more in-depth explanations could be provided in subsequent sections. The importance of including visual elements, such as flow charts, to complement text was also stressed. Lastly, many participants pointed out that the use of examples and references is helpful.

Results – Influencing factors

Both literature and experts indicated that the influencing factors can typically be classified across the themes of social and cultural, governance, informational and technological, physical and ecological, financial, political, and legal. The following factors were considered important by interviewees.

Within the social and cultural domain, awareness and understanding, acceptance and support, and interests and priorities vary among citizens and can be addressed by employing several strategies, including informing citizens about NBS and their benefits, framing NBS in ways that align with citizens’ values and priorities, stimulating citizen-led initiatives, and letting citizens participate in multiple forms, ranging from incorporating citizens’ perspectives to co-creation and active involvement in maintenance. Drivers within this domain include the ability of NBS to enhance citizens’ quality of life and to foster a sense of place and ownership.

When it comes to governance, limited collaboration between departments, organizations, and sectors hinders NBS adoption. To foster multi-stakeholder collaboration, the use of co-creation and communication tools, the establishment of construction or thematic groups, and the strategic linking of NBS to urban agendas can be of help. Moreover, assigning responsibility to stakeholders, through multi-level governance structures, national or municipal leadership, or citizen-led stewardship, is vital. While formal networks can serve as platforms for connecting practitioners, exchanging knowledge, and facilitating cooperation on NBS projects, informal personal relationships also play a critical role in driving collaboration.

For the informational and technological aspects, key factors include data availability, expressibility, measurability, and predictability, as well as the presence of appropriate tools. Although data on NBS is becoming increasingly available, several barriers persist: lack of open access to data, the absence of a data overview, the challenge of expressing certain variables quantitatively or monetarily, difficulties in identifying the right tool for specific purposes, and the fact that existing tools often only offer a snapshot of NBS outcomes. To address this, several strategies can be employed, such as developing a comprehensive data overview, using averages or proxies in calculations, combining qualitative and quantitative methods, creating an overview of available tools, and employing scenario modeling to explore long-term effects. Moreover, Urban Living Labs can help with knowledge generation and data collection and catalogs with example NBS projects can help practitioners learn about the possibilities.

Within the physical and ecological system, the benefits delivered by NBS, including increased air quality, enhanced biodiversity, and reduced flood risk, serve as key drivers for their adoption. Moreover, the inherent adaptability and multifunctionality of NBS further promote their implementation. However, the general lack of space within cities, limited availability of suitable locations, existing systems in place, and maintenance requirements form hindrances. To address these barriers, strategies like assigning multiple functions to NBS, optimizing soil use, implementing hybrid solutions, and using zero maintenance species can be of help.

Within the financial realm, the (maintenance) costs is an important factor. While some argue that the costs are higher, others point out that the percentual difference is minimal, especially given the increase in property value. Making a strong business case is also experienced as challenging: while NBS provide an array of benefits, they are difficult to express in monetary value and are often enjoyed by others than those who bear the costs. Next to this, financial flows within governments are often separated for each department. Combining departmental financing streams, establishing co-financing models, using subsidies, and comparing the costs of NBS with grey solutions, are strategies that can aid in addressing these factors.

For the political theme, the existence of political interest in and prioritization of NBS is vital for its adoption. Participants indicated that NBS are currently not often on the priority list of politicians. To create a supportive political landscape and reduce vulnerability to political cycles, a helpful strategy would be to embed NBS in long-term planning frameworks. Equally important is the presence of supportive and coherent policies for NBS, of which both the Netherlands and the EU have some in place. Despite this, interviewees felt that the current set can be expanded and that cities can take inspiration from each other’s policies.

Lastly, factors within the legal landscape are of influence. Land ownership can act as a barrier, as governments have limited say over what private property owners should implement, and quite a large area of the city is privately owned. Another important factor is the regulations in place, of which some currently make NBS implementation difficult or impossible. However, there are also several supportive regulations in force in the EU and various Dutch cities, of which the latter can serve as measures that can be copied in other cities: implementing a no loss or biodiversity net gain regulation, creating a NBS point system, mandating the inclusion of greenery/water storage, or mandating pavement removal.

Results – Seeds of Change Framework
The insights from literature and experts are synthesized in the Seeds of Change Framework, which is a guiding implementation framework that enables users to systematically identify the barriers and drivers that influence their NBS projects, as well as select the strategies and measures that can be applied to address these factors or to generally stimulate implementation. In addition, it highlights the principles that should be followed to ensure sound practice. The primary application of the framework is prospective, guiding decision-making and design during the planning and implementation phases of NBS projects, but it can also be applied retrospectively to evaluate what went well, identify areas for improvement, and draw lessons for future projects. The framework consists of three chapters. The first chapter introduces the framework by explaining NBS, the necessity of the framework, what it does, who can use it, what it looks like, and how it can be used. This is followed by the second chapter that contains tables for identifying barriers and drivers, selecting strategies and measures, and becoming aware of principles. The first table lists influencing factors for which stakeholders must identify whether they function as a barrier, driver, or both. Next, the framework asks stakeholders to assess the relevance of each factor. The following column refers to numbered strategies and measures that can be selected to address each factor. Separate tables list the strategies and measures as well as the principles, each with a unique number. The third chapter provides one-line definitions for each factor, along with expert comments and illustrative cases for selected factors. The illustrative cases are realized NBS projects that show how the content of the framework can be found in practice.

Contributions to literature
The thesis contributes to literature by providing a comprehensive understanding of the barriers and drivers that affect NBS implementation in Dutch urban contexts, the strategies and measures that can be applied to address these factors or generally support implementation, and the principles that can be followed to ensure sound adoption. It is novel in that it focuses on NBS specifically, considers the Dutch urban context, identifies all factor types within a single study, and treats all of them with equal importance. In doing so, the research also contributes to explaining the existing implementation gap. Moreover, testing hypotheses on these factors revealed which of the factors identified in literature play a part in practice within Dutch cities. It also showed that some factors previously assumed to be barriers can in fact act as drivers, or even both, and vice versa. The nuances in experts’ responses as well as the (subtle) differences in perspectives among participants, further confirmed that factors are highly context-dependent. Finally, the study contributes to the landscape of NBS frameworks that can be used during the planning and implementation phases of projects. By incorporating all factors into a single tool, the thesis provides an implementation framework that can guide stakeholders toward more widespread and successful NBS implementation.

Recommendations for practice
For stakeholders involved in the planning and implementation of NBS projects, it is recommended that they become aware of the most critical factors. Each stakeholder group should act on this knowledge in ways that align with their specific roles, responsibilities, and capacities, addressing the factors they are best positioned to influence. Regarding the use of the Seeds of Change Framework, it is advised that all involved stakeholders apply the framework at the start of the project to create a shared understanding of the influencing factors. As application of the framework is limited by the knowledge and experience of its users, they should collect and analyze data to verify their assumptions about potential barriers and drivers. Before applying the framework to current NBS projects, stakeholders are encouraged to first use it retrospectively on a completed project in which they were involved to gain hands-on experience with the framework as well as to practice critical reflection.