Humboldt University, Germany
Nature-based Solutions (NBS) are living solutions inspired and supported by the use of natural processes and structures, and are designed to address various environmental challenges in an efficient and adaptable manner, while simultaneously providing economic, social, and environmental benefits (European Commission, 2015). The core idea of NBS is to use the benefits of ecosystem services to prevent a system from crossing a certain threshold/tipping point, such as critical air temperatures, water shortages. or water levels that could lead to dangerous flooding. These interventions create net positive effects, e.g., clean air (Nowak et al., 2014), cooler air temperatures (Baró et al., 2014; Kain et al., 2016), and flood or coastal protection (Wright & Scott, 2011). Types of NBS relevant to cities include: ecosystem restoration, greening of grey surfaces (e.g., green rooftops, green walls or greened brownfields), and integrated broad scale climate change mitigation and adaptation measures, e.g., afforestation, natural flood control, constructed wetlands and, potentially, geoengineering.
The term “Nature-based solutions” has been in use since 2012 by the International Union for the Conservation of Nature (IUCN) in order to promote the role of nature and natural spaces in providing climate mitigation options and when facing adaptation challenges (IUCN, 2012). The European Commission provides a strong impetus through its new framework programme for research and innovation (Horizon 2020) through which NBS are used to provide a new narrative for research and development activities involving biodiversity and ecosystem services by aligning this type of research with a strong focus on innovation for job creation (European Commission, 2015). NBS had already emerged in publications of joint EU research activities (e.g., Potschin et al., 2015), but only recently started being covered by research papers explicitly in this new framing/context (e.g., Eggermont et al., 2015; Maes & Jacobs, 2015).
Examples of NBS in Europe
A recent review of existing projects in various stages of implementation shows the potential of NBS to impact urban land use change in Europe. Many actions focus on the transition of grey infrastructure or brownfields into greenspaces, such as in Gomeznarro Park in Madrid, Spain, where about 10,000 square meters of its land area was completely restructured, including replacing impervious pavements with permeable surfaces, thereby facilitating water drainage and collection. As well, a system of underground storage tanks were installed for water collection and distribution. Eroded or compacted soil was replaced in order to enable re-vegetation in these places (click here to see other examples of NBS in Europe).
Another example is Nijmegen, The Netherlands, where the city started a wide range of greening activities, including green walls, parks, planted and potted trees as well as the creation of a park from a former parking lot in order to face the challenges of public health and climate adaptation (http://www.future-cities.eu/). More illustrative examples of possible NBS in cities involving land and ecosystems are shown in Figure 1.
Figure 1. Nature-based solutions for sustainable cities that involve land area and land use change (Photos by Dagmar Haase)
NBS often involve larger parts of the urban area as they make use of existing natural elements and remnants of nature in the cities, such as wetlands, rivers, mountains/rocks or forests. Most examples in Europe stem from lowland cities in the Netherlands, Spain, Germany, UK, or Italy, where large space potentials are given. However, all cities have spaces that could potentially be utilized for NBS, such as buildings redesigned to have rooftop gardens, the construction of living walls, or planting trees along streets without being dependent on large remnants of nature such as rivers, creeks or dead river channels (Kain et al., 2016).
Compared to traditional construction approaches predominantly used in flood and storm water management, NBS are “low-impact” strategies, not only in terms of the level of protection they provide but also the level of risk in case they fail. For example, a reconstructed wetland is able to store a defined amount of water for a period of time until the soil and sediment saturation threshold is reached, but will never be “safe” up to a specific water level as dams and dikes presume to be (McCallum & Heming, 2006). If NBS fail, risks are lower as they tend not to fail in catastrophic ways, e.g., if a dam fails. Nevertheless, for people living nearby, a certain amount of safety is given by the functioning wetland and, what is more, the soils store the surplus water for balancing drought periods that might follow a flood, especially in summer.
Long-term challenges for the use of NBS in cities
There are several keys questions that can help define what make NBS a sustainable and complementary concept to land use and land system science, and why. The following questions can provide a logical framework for distinguishing NBS from inefficient and/or potentially harmful solutions.
What city-centric challenges can NBS solve?
The better the definition and specification of what the challenges are that nature or a nature-based design must solve, the better the response of ecosystems and/or ecosystem components could be. Thus, we need a comprehensive list of such challenges and problems. Moreover, knowledge of the persistence, spatio-temporal extent, complexity, and the involvement of the socio-economic-environmental and technical systems of a city in these challenges is needed. Who is involved in the design and the implementation of NBS? Which stakeholder groups must be informed and involved in the co-development processes and which funding opportunities exist for the long-term monitoring of NBS?
How is nature framed in NBS?
When discussing NBS, are we only referring to biotic nature – that is first and foremost plants and to a lesser extent animals, or are abiotic ecosystem components (e.g., soils, water, thermal energy) and related processes included as well? Do urban ecosystems include artificial grey structures and humans? Considering the examples shown above in Figure 1 (e.g., constructed wetlands and bioswales), human capital (knowledge, communication) is essential to NBS. Concepts such as green infrastructure only marginally involve abiotic ecosystem dimensions and resources such as soils or sediments so that they fail in making use of their capacities to serve to face challenges such as clean water supply or waste management in cities. Here, NBS are a more complete approach to provide water and to store/fix waste/pollutants. However, as some NBS might include the alteration of nature (e.g., by favoring one ecosystem service or certain species over another and to what extent can NBS be altered in order to accepted by nature and its processes? Is the optimization of street trees driven by their leaf area index and water demand considered a NBS to the challenge of heat in cities while consciously accepting a decrease in biodiversity? Answers to these questions would help to define potentials and limitations of the NBS’s approach.
How can NBS deal with the challenges of urban complexity?
The problems associated with biodiversity conservation, human well-being, and sustainability are complex and full of trade-offs. How can NBS deal with these complexities? It may be that they are complementary to other concepts/approaches that focus less on a pure problem solution rather than on a system integration and diversity enhancement in order to develop resilient cities. Thus, NBS would represent a “module” in socio-ecological-technical systems (McPhearson et al., 2016). NBS should not emphasize replacing technological solutions, as humans will continue to develop techniques to solve problems that affect their livelihoods (Van den Hove et al., 2012).
How can NBS be used to make cities more inclusive?
There have been increasing discussions on how and to what extent greening strategies carry the risk of fostering greater inequality among social groups instead of fostering social coherence. Green space implementation can lead to an increase in the attractiveness of a residential area and to a higher quality of life as well as other environmental benefits. However, due to rising housing costs, these benefits might be limited to those households who can afford the higher costs and could displace low income, less affluent populations. In contrast, and what could strongly support NBS as a concept and an approach in cities and urban agglomerations is to ensure that all relevant stakeholders at various scales and all the concerned sectors are addressed and involved. NBS should contribute to social inclusiveness and lead to social cohesion and equity in cities through a more democratic design process.
Today, our world faces many challenges, such as climate change, food security, healthy living conditions and water security. With complementary technological approaches, nature can play a much stronger role in tackling these challenges and make urban and rural systems more resilient to change. Perhaps most important is the educational and learning impact that an active implementation of NBS will have on those who live more and more in cities and urban areas.
When reflecting upon the potential trade-offs and limitations of NBS, it is not to disparage but to highlight the importance and relevance of NBS for sustainable and livable cities. More precisely, NBS can address connections with other goals of sustainable urban development, resilient cities, and the promotion of the health and wealth of urban residents. In the future, we should explore the transformative potential for increasing goods and services of urban nature for people, and to balance environmental burdens in urban areas.
Dr. Dagmar Haase is Professor of Landscape Ecology at Humboldt University in Berlin, Germany. She is also a member of the scientific staff of the Centre for Environmental Research (UFZ) in the Department of Applied Landscape Ecology.