Nature-based solutions in the urban context: terminology, classification and scoring for urban challenges and ecosystem services

Abstract

The concept of Nature-Based Solutions (NBS) has emerged to foster sustainable development by transversally addressing social, economic, and environmental urban challenges. However, there is still a considerable lack of agreement on the conceptualization of NBS, especially concerning typologies, nomenclature, and performance assessments in terms of ecosystem services (ES) and urban challenges (UC).Therefore, this article consolidates the knowledge from 4 European projects to set a path for a common understanding of NBS and thus, facilitate their mainstreaming. To do so, firstly, we performed elicitation workshops to develop an integrative list of NBS, based on the identification of overlaps among NBS from different projects. The terminologies were formalized via web-based surveys. Secondly, the NBS were clustered, following a conceptual hierarchical classification. Thirdly, we developed an integrative assessment of NBS performance (ES and UC) based on the qualitative evaluations from each project. Afterwards, we run a PCA and calculated the evenness index to explore patterns among NBS. The main conceptual advancement resides in providing a list of 32 NBS and putting forward two novel NBS categories: NBS units (NBSu) that are stand-alone green technologies or green urban spaces, which can be combined with other solutions (nature-

Nature-Based Solutions and Circularity in Cities

“…Their implementation can be either as a single unit or in combination with other NBS, conventional technologies or existing urban infrastructures [13], and thus, such classification is in line with the principles of CE. NBS interventions refer to measures and bioengineering techniques applied in specific ecosystems or other NBS_u to support natural processes such as river flow dynamics (NBS river interventions (NBS_ri)), soil quality (NBS soil interventions (NBS_si)), and biodiversity (NBS biodiversity interventions (NBS_bi)) [13]. This conceptual framework was built in the frame of the COST Action Circular City, in order to support the selection and characterisation of NBS_u and NBS_i, with potential to tackle urban circularity challenges (UCC), i.e., to create a list of NBS under the 'NBS Circular Framework'.…”

“…Among many definitions of NBS, there is one predominant agreement, i.e., bringing nature in cities. 'Nature' is often understood as 'the green factor´indicating presence of vegetation [13]. Nevertheless, such statement might eliminate a full range of solutions that employ nature via natural processes, such as microbiological processes or for example (bio)filtration through natural porous material.…”

“…To clarify the meaning of the NBS concept is as important as defining a common set of NBS in order to facilitate its implementation and monitoring. In this sense, Castellar et al [13] propose a common list of 32 NBS, by revising more than 200 NBS defined in four European projects (UNALAB [14]; NATURE4CITIES [15]; THINKNATURE [16]; URBANGREENUP [17]). Moreover, the authors disclose a conceptual advancement in terms of understanding the role of NBS in urban settlements by proposing two novel typologies: NBS units (NBS_u) and NBS interventions (NBS_i).…”

“…According to Castellar et al [13], NBS_u stands for single green technologies (NBS_technological units (NBS_tu)) or urban green space (NBS_spatial units (NBS_su)) replicating processes occurring in nature to enhance the performance of natural capital in cities. Their implementation can be either as a single unit or in combination with other NBS, conventional technologies or existing urban infrastructures [13], and thus, such classification is in line with the principles of CE.…”

“…According to Castellar et al [13], NBS_u stands for single green technologies (NBS_technological units (NBS_tu)) or urban green space (NBS_spatial units (NBS_su)) replicating processes occurring in nature to enhance the performance of natural capital in cities. Their implementation can be either as a single unit or in combination with other NBS, conventional technologies or existing urban infrastructures [13], and thus, such classification is in line with the principles of CE. NBS interventions refer to measures and bioengineering techniques applied in specific ecosystems or other NBS_u to support natural processes such as river flow dynamics (NBS river interventions (NBS_ri)), soil quality (NBS soil interventions (NBS_si)), and biodiversity (NBS biodiversity interventions (NBS_bi)) [13].…”