Nature-based solutions for urban sustainability

Nature-based Solutions for Urban Sustainability

Cities across the globe face growing sustainability and resilience challenges that will require innovative solutions and collaborative partnerships. The pace of climate change, the frequency and duration of unprecedented climate-related events, threats to biodiversity, and the concentration of people and outdated infrastructure in cities demand new strategies to ensure that cities are livable, resilient, and equitable. Nature-based solutions (NbS) are at the forefront of addressing impacts of climate change, especially in urban planning, practice, and research. A growing number of cities worldwide are exploring NbS, sometimes referred to as green infrastructure, urban nature, ecosystem-based adaptations, or simply environmental restoration or conservation (1). NbS incorporate natural processes to support adaptation to climate change and urbanization, as well as the restoration of ecological functions (Fig. 1). While emphasized as a tool to address climate change in cities, NbS are also promoted for their benefits to individuals and communities, including improved public health, access to nature, and social equity (2, 3). In contrast to traditional engineered urban infrastructure that is mostly rigid and inflexible over time, NbS provide flexibility to confront the shifting impacts of climate change and uncertainty of the future (4, 5).

Fig. 1.

Examples of urban NbS supporting climate resilience: (A) Benjakitti Forest Park in Bangkok is a constructed wetland and green space transformed from a former industrial site (Photo courtesy of Erich Wolff). It manages stormwater, enhances biodiversity, and improves water quality. Using recycled materials and preserving existing trees, the park supports urban resilience, climate adaptation, and community well-being through sustainable, ecological design; (B) Lincoln Park in Chicago functions as a NbS through its restored ponds, wetlands, and natural areas that manage stormwater, enhance biodiversity, and reduce urban heat. Being a public park, its ecological features contribute to climate resilience and public well-being in a dense urban environment (Photo by Nancy Bourque on Pexels); (C) Wohnpark Alt-Erlaa in Vienna is an early example of urban NbS, featuring terraced green balconies that enhance air quality, reduce heat, and support resident well-being (Photo by Nick Night on Unsplash). Though not originally designed as NbS, it integrates vegetation into urban living, offering ecological and social benefits aligned with contemporary NbS principles.

In keeping pace with accelerating interest in urban NbS worldwide, key principles, frameworks, and classification schemes are emerging to understand and advance NbS (6–11). Not only has there been an explosion of research on NbS in the last 10 years, there have also been new local, national, and international development directives supporting NbS implementation. For example, NbS have gained strong support in local climate adaptation plans (12) and national policy agendas within the United States, where the Biden Administration Executive Order 14072 (13) centered NbS for climate adaptation and mitigation alongside biodiversity protection. NbS are also emerging in international agendas through the European Union Horizon 2020 (14), International Union of Conservation of Nature (15), United Nations (UN) (16), Intergovernmental Panel on Climate Change (17), and the World Economic Forum (18).

Despite rapid uptake in policy, uncertainties remain about scaling up and scaling out of NbS to address climate change in cities, particularly in diverse social–cultural, governance, ecological–biophysical, climatic, and infrastructural contexts (19). For example, while NbS are expected to be versatile, multifunctional, and help mitigate the impact of climate risks, the full suite of NbS benefits and potential tradeoffs is uncertain, particularly under changing climate and more severe extreme weather-related events (4, 20–22). The recent frameworks on urban NbS have largely emerged from the Global North, and the application of these frameworks in other contexts, such as in the Global South, informal urban settlements, or from Indigenous perspectives, is not always appropriate (23–26). Moreover, in some global regions, such as Latin America and the Caribbean, urban NbS are predominantly seen (and reported upon) in the wealthiest or largest nations and cities; NbS are less systematically studied elsewhere in the Latin America region, despite likely broad implementation through bottom–up or un-funded initiatives (27, 28). Continued efforts studying place-based design, implementation, and functioning of NbS across diverse global contexts will provide an important solution-set for addressing future urban sustainability and resilience challenges.

The objective of this paper is to introduce a Special Feature: “Nature-based Solutions for Urban Sustainability”—a collection of four articles addressing the current state of global urban NbS science and conceptual framings. The special feature explores opportunities for research and practice to scale up NbS to address equity, justice, and inclusion while enabling transformation in urbanized areas. The special feature includes a review and three perspectives papers that leverage learnings from NATURA (NATure-based Solutions for Urban Resilience in the Anthropocene), an international network of networks that connects academic researchers and practitioners around the world and provides a critical platform for knowledge exchange. The works in the special feature build upon the progress made through global collaborations on urban NbS within NATURA. Here, we briefly introduce NATURA, overview urban NbS and the ongoing needs related to urban NbS, and then introduce the special feature papers that address these needs.

Framing NbS Science and Practice from a Global Network of Networks

Funded by the US NSF in 2019, NATURA is a network of networks, each of which addresses urban NbS in their individual work. NATURA seeks to advance the understanding of NbS as a tool for urban resilience in the face of climate change and climate extremes. NATURA’s objective is to enhance connectivity among the world’s NbS networks, including the research community (e.g., natural, geophysical, and social scientists, engineers, and landscape architects), city practitioners (e.g., officials from city, county, or state governments), members of nongovernmental organizations, community leaders, and private business design and implementation firms. NATURA draws together networks from seven regions of the globe (the United States and Canada, Latin America and the Caribbean, Europe, the Middle East and North Africa, sub-Saharan Africa, Asia, and Oceania) and has grown since 2019 to include 46 networks across the seven regions (Fig. 2). For example, NATURA includes global NbS networks such as The Nature of Cities, The Nature Conservancy, and Cities with Nature, as well as regionally focused networks such as Go GreenRoutes, Oppla, and Kounkuey Design Initiatives, all of which primarily focus on NbS in urban environments. These global and regional networks are examples of key institutional actors building the capacity for and implementation of urban NbS.

Fig. 2.

NbS networks engaged with NATURA across seven global regions.

NATURA applies a social–ecological–technological systems (SETS) framework to study urban systems and NbS. The SETS framework recognizes cities as complex, interdependent systems (29–32). Inclusive of multiple disciplines and practices, the SETS framing recognizes that siloed approaches and single-disciplinary framings are insufficient to navigate the complexities of urban systems threatened by climate hazards and unknown futures (33). In particular, through SETS, NATURA integrates the study and understanding of interconnected social dimensions, including governance, culture, healthcare, and economy; ecological dimensions, including the ecosystems that constitute the urban environment and ecological-based infrastructure; and technological-engineered infrastructure dimensions, including transportation networks, roads, buildings, energy, water, as well as information and technology. The SETS framing and NbS are also critical in addressing climate change challenges and development in more rural settings (19); however, NATURA and the focus here in the special feature are on urban NbS.

When NATURA first initiated, we leveraged the unique opportunity of the NATURA global network of networks to explore the state of the science and practice of urban NbS. We gathered perspectives from over 150 network partners about current and long-term knowledge gaps and opportunities related to urban NbS. Reflecting NATURA’s membership in 2020, the gaps were primarily identified by academics in North America and Europe, though contributions were made from all global regions and sectors—including perspectives from academia, government and practitioner representatives, private industry, and civic organizations. The identified gaps revealed critical research and practice needs for mainstreaming and improving effectiveness of NbS in urban contexts across SETS domains and various sectors, institutions, and regional contexts. Here, harnessing the innovation, creativity, and knowledge from those international urban contexts, we highlight the identified knowledge gaps that continue to frame the ongoing work of NATURA and its collaborators, including the works in this special feature.

Reflecting the social domain of SETS, NATURA members noted that community engagement, public buy-in, effective policies, and knowledge-action exchange are crucial for successful NbS deployment (Fig. 3). An identified need was for more inclusive engagement strategies that foster strong community involvement in planning, implementation, and stewardship of the NbS, ensuring that local residents are both engaged in and benefit from NbS projects. At the same time, it was identified that NbS goals should be aligned with decision-makers’ needs in order to create buy-in and an enabling regulatory environment for these solutions to thrive. Research on effective public engagement mechanisms and policy alignment is needed to bridge this gap.

Fig. 3.

Knowledge gaps and challenges related to urban NbS within the SETS framework as identified by NATURA members at the founding of the network of networks (2020). Circles are sized based on relative number of mentions. Responses reflected a bias in representation of Europe and North America among regions and in academia, which is consistent with the distribution of literature and an indication of the bias among network founders.

While identified as a challenge across all regions, collaborators in sub-Saharan Africa particularly called out barriers to NbS adoption that were rooted in policy, governance, and political will—such that coherent policies and regulatory frameworks supporting NbS were lacking. Limited political commitment and competing priorities were identified as further impeding progress. Strengthening governance structures and fostering political support are essential steps toward overcoming these obstacles and unlocking the potential of NbS in cities.

While applied research on NbS is extensive, translating these insights into actionable solutions through knowledge-action exchange remains difficult. A major challenge identified was the gap between scientific research on NbS and its practical application. Academics in North America commonly identified the need to improve communication and exchanges with practitioners—both to learn from experiences of practitioners in NbS implementation, as well as to improve implementation standards based on empirical research. Enhancing data-sharing platforms and fostering collaborative networks can be important mechanisms to ensure that scientific insights are more effectively integrated with on-the-ground practices.

A common challenge identified in the social–ecological domain involved the need for comprehensive and integrated socio-economic and ecological assessment frameworks. While NbS projects often highlight ecological impacts, there is an ongoing need to develop integrated assessments that also measure their multifunctionality and the synergies or trade-offs related to public health, social well-being, community cohesion, and economic investments. Integrating economic cost assessments is critical to consider the funding needed for implementation and maintenance of NbS. For example, in the private sector, businesses noted needing clearer insights into how NbS can contribute to their sustainability efforts, reduce operational risks, and offer economic advantages. Providing case studies and guidelines that showcase the economic and environmental benefits of NbS investments will be an opportunity to encourage greater private-sector participation in NbS initiatives.

From an ecological perspective, a commonly identified need across all regions was a better understanding of how to optimize and assess the role of natural ecosystems. This includes addressing the adaptability of NbS under changing conditions and the provisioning of ecosystem benefits from NbS (Fig. 3). For example, Latin American regional members recognized the potential of NbS to enhance biodiversity and ecosystem services, but noted there was a lack of empirical research quantifying these benefits in diverse contexts. Similarly, public and civic organizations emphasized the potential role of NbS in addressing water-related challenges, including flooding and water quality or conservation challenges, but highlighted more work is needed to understand the role of NbS in water management under changing conditions. Further work documenting and long-term monitoring of NbS will help to capture the full suite of ecosystem outcomes and explore how NbS can manage stormwater, improve water quality, and secure sustainable urban water resources.

Similar challenges were highlighted in the ecological-technological domain of integrating NbS into existing urban infrastructure. Designing NbS that are compatible with densely built environments, while also enhancing ecological functions, was noted as a significant hurdle. Urban planners and engineers need more research on how to harmonize NbS with infrastructure without compromising its functional and structural integrity. Such integration is key to maximizing the benefits of NbS in cities.

In the technological-infrastructure domain, NATURA members noted a lack of robust performance monitoring and impact assessments (Fig. 3). While noted broadly across NATURA, those working in government and practice, as well as in the Asia-Pacific region, identified this as a key challenge over other challenges. Currently, inconsistencies in methodologies and the lack of standardized metrics hinder long-term evaluations of NbS success. Effective NbS deployment requires robust tools and methodologies to measure their success, particularly in enhancing urban climate resilience. The development of standardized indicators and benchmarks that can be universally applied will help governments evaluate NbS performance and track progress toward sustainability goals. Establishing reliable monitoring frameworks is essential to ensure that NbS remain effective and adaptable to evolving environmental and social conditions, especially in the face of growing climate impacts (e.g., hydrologic risks, extreme heat), natural disasters, and socio-economic vulnerabilities.

Another key gap in the technological domain revolved around guidance on technical feasibility, design, and implementation approaches. Urban complexity requires innovative, adaptable, cost-effective, and scalable NbS. However, there is currently a gap in practical design strategies that can accommodate the distinct and dynamic needs of urban spaces. Addressing this gap involves developing new methodologies and design practices that consider both technical feasibility and ecological benefits.

Looking to the future, continued innovation in NbS design will be necessary to address emerging urban challenges, including unpredictable and uncertain future climate-related events. Innovations may focus on developing new materials, technologies, methodologies, and safe-to-fail design approaches that enhance the effectiveness and adaptability of NbS. Innovation will also require centering participatory methods that draw on diverse approaches and knowledge to advance the transformative potential of NbS. More research is needed to ensure NbS can provide robust solutions to face the uncertainties of changing conditions.

Finally, intersecting all domains, equity and justice were identified as key concerns. This gap was more commonly noted in the Global North, for example where Europe’s relatively advanced NbS landscape still grapples with issues of equity, justice, and social benefits. Inclusive approaches can ensure that marginalized communities are not left behind in the design, planning, deployment, and multifunctional benefits of NbS, nor are they disproportionately impacted by unintended tradeoffs of NbS deployment. Further research is needed to assess the broader social benefits of NbS, including their impact on human well-being and social cohesion.

Forward Progress and Future Opportunities

Despite significant progress since the inception of NATURA, still more work is needed to further address the gaps and opportunities for urban NbS across SETS domains. The articles included in this special feature elaborate on the current global, regional, and place-based challenges and opportunities for more effective, impactful, and equitable urban NbS. The special feature articles include: a synthesis of global reviews on NbS (28), a perspective on principles for guiding transformative potential and equitable outcomes of NbS (34), a perspective on the radical, place-based levers needed to address power dynamics in adoption of NbS (35), and a critique and expansion of the framing of NbS from Indigenous perspectives (26). Together, these papers chart a path forward in opportunities to advance innovations in frameworks, research, and implementation of NbS.

In contribution to this special feature, McPhearson et al. (28) expand upon the current key challenges of NbS for addressing urban sustainability across diverse biophysical, socio-economic-cultural, and governance contexts in the Global North and Global South. Drawing on a global synthesis of review articles and expert assessment within seven global regions, this paper highlights how local and regional contexts are critical to effective NbS implementation. The review discusses the cutting edge of innovation in NbS and where ongoing challenges lie. Through the global review and regional insights, the paper makes clear the needed paths forward for fostering innovation and knowledge sharing locally and across regions and sectors, such that assessment, financing, political will, and participatory processes for planning, implementation, and management will lead to just and equitable benefits and outcomes.

Also in this special feature, Frantzeskaki et al. (34) identify guiding principles and processes needed to make progress on addressing the identified challenges, particularly those associated with just transitions to urban NbS. The authors center the core principles of inclusivity and justice in inter- and transdisciplinary research, as well as design, planning, and implementation of NbS. They argue that collaboration with diverse and inclusive participants in both research and application ensures a holistic examination of NbS and their contribution toward just and transformative urban systems.

Further delving into the short and long-term transformative potential of NbS, Diep and McPhearson (35) propose four levers to radically transform the way cities adopt nature-based adaptations to address climate challenges. To leverage the transformative potential of NbS, the paper highlights the importance of addressing power dynamics while acknowledging the socio-institutional factors and contexts in which urban NbS exist. While levers for transformation apply in other nonurban areas, the paper draws from successful urban examples of NbS in Latin America, Africa, Europe, and the United States. The authors emphasize the need for inclusive knowledge production, transparent and open knowledge sharing that is accessible to broad audiences, incentive-based policies that bridge the gap between initial investment and long-term maintenance for benefits, new mechanisms for integrating financial and nonfinancial resources and partnerships, and reflexive monitoring and evaluation that draws on community perspectives and values.

Finally, Nelson and Reed (26) reflect on Indigenous perspectives, concerns, and critiques of NbS concepts, particularly as applied in urban environments. The authors argue that there has been an epistemic erasure of Indigenous knowledges from NbS frameworks and that concepts and framing of Indigenous Knowledge Systems and Traditional Ecological Knowledge have thus far not been given sufficient attention in NbS scholarship and practice—despite a long history of Indigenous Peoples’ engagement with and protection of nature and biodiversity. In particular, Indigenous perspectives and approaches incorporate “bioculturally-based solutions” that capture the concepts of biocultural diversity and heritage and do not make a distinction between nature and culture. The article concludes with recommendations for transparent and decolonial practices that will lead to the more just framing and implementation of NbS.

As cities turn to NbS to address the impacts of a changing world, there are ongoing knowledge gaps and implementation challenges—particularly given uncertainties about future climate change conditions. While much work is yet to be done to address the short and long-term gaps and challenges related to NbS, collaborative networks, such as NATURA, and the special feature papers highlight the opportunities and need for a concerted effort to close these gaps through collaborative research, policy innovation, cross-sectoral partnerships, and looking to other ways of knowing.