Nature-Based Solutions for Agriculture in Circular Cities: Challenges, Gaps, and Opportunities

Nature-based solutions for improving food security: A systematic global review

Nature-based solutions (NBS) have been promoted as a holistic way to solve a variety of societal issues while benefiting biodiversity at the same time. To date, applications of NBS approaches that help ensure food security have yet been systematically reviewed. In this paper, we critically review the specific NBS for food security, highlighting their limitations, to provide recommendations that promote their applications for improving global food security. We accessed and evaluated publications on four different scholastic databases, and our systematic review of relevant materials indicated that many NBS approaches can be applied to enhance food security dimensions individually or together. However, there is a strong bias towards food availability, and not enough research has been done to link NBS with improvements in food access and utilization. Over 80 % of the reviewed papers were of short-term studies or without specific timeframes, and 25 % offered no information on the economic effectiveness of NBS. Environmental benefits of NBS were explicitly described in about 60 % of these papers, and biodiversity enhancement was measured in only about 10 %. We, therefore, recommend future applications of NBS to safeguard food security be shifted to food access and utilization with careful consultation with local communities to address their specific context, using indicators that are easily measured and managed. Systematic monitoring regimes and robust and diversified financial support systems are also equally important in efforts to successfully implement NBS. Moreover, environmental and societal benefits, especially water productivity and biodiversity, must be incorporated into the planning and design of NBS.

What does it take to renature cities? An expert-based analysis of barriers and strategies for the implementation of nature-based solutions

This paper uses an expert-based methodology to survey the barriers and strategies related to the implementation of nature-based solutions (NBS). The ambition of the paper is to offer a bird's eye overview of the difficulties encountered by NBS deployment and ways to overcome them. With a wide participation of 80 experts from COST Action Circular City, we identify barriers specific to 35 pre-defined NBS of the following four categories: Vertical Greening Systems and Green Roofs; Food and Biomass Production; Rainwater Management; and Remediation, Treatment, and Recovery. The research sheds light on how a major interdisciplinary - yet predominantly technically-oriented - community of scientists and practitioners views this important topic. Overall, the most relevant barriers are related to technological complexity, lack of skilled staff and training programs and the lack of awareness that NBS is an option. Our results highlight concerns related to post implementation issues, especially operation and maintenance, which subsequently affect social acceptance. The paper identifies a "chain" effect across barriers, meaning that one barrier can affect the existence or the relevance of other barriers. In terms of strategies, most of them target governance, information, and education aspects, despite the predominantly technical expertise of the participants. The study innovates with respect to state-of-the-art research by showing a fine-grained connection between barriers, strategies and individual NBS and categories, a level of detail which is not encountered in any other study to date.

Challenges to Promote Sustainability in Urban Agriculture Models: A Review

Urban agriculture (UA) can be used as an action to promote sustainability in cities and inform public health policies for urban populations. Despite this growing recognition, its implementation still presents challenges in countries in the Global North and Global South.

BACKGROUND

In this context, this systematic review aims to identify the development of frameworks for the implementation of UA as a sustainable action and its main opportunities and shortcomings in meeting urban socio-environmental demands.

METHODS

In this review, using the PRISMA protocol, we evaluated 26 studies on the interplay between UA and sustainability surveyed on the Web of Science to provide an overview of the state of the art.

CONCLUSIONS

In summary, it was possible to identify many key challenges in UA adoption, which regard air and soil contamination, availability of green areas, layout of urban infrastructure, food distribution, among others. Due to numerous socio-economic and environmental contextual factors in cities, especially when comparing realities of the Global North and Global South, there is a need to develop a model that can be adaptable to these different contexts. Thus, it is recognized that the concept of sustainability does not present a universal understanding and that in its search it could be argued that one of the most important gaps is still to address social issues in relation to environmental ones.

Biodiversity in Urban Green Space: A Bibliometric Review on the Current Research Field and Its Prospects

Understanding the development process of urban green space and biodiversity conservation strategies in urban green space is vital for sustainable urban development. However, a systematic review of the urban green space biodiversity research is still lacking. We have retrieved 3806 articles in WOS core journals and carried out the bibliometrics analysis through the three related search terms: urban, green space, and biodiversity. We found that: (1) the year 2009 was a changing point, and the number of articles have increased exponentially since 2009. The United States, China, Europe, and Australia are closely linked, and four research centers have formed; (2) all studies can be classified into three research themes: "Pattern of Urban Green Biodiversity", "Ecological Function of Urban Green Biodiversity", and "Sustainability of Urban Green Biodiversity"; (3) based on the evolution of keywords, this field is divided into the budding stage (1998-2012) and the development stage (2012-2021). The keywords in the budding stage focus on the diversity of different species, and the keywords in the development stage focus on the ecosystem services, biodiversity protection, and residents' satisfaction; (4) the future research focus may be in three aspects: studies on green space in the less urbanized area and urban-rural ecotone, the regulation mechanism and cultural services of urban green space, and the rational layout and management of urban green space. This study hopes to provide a reference for future research on urban green space biodiversity and promote the sustainable development of urban green space.

Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro- or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges.