۱٫ Introduction

۲٫ Characteristics of the conceptual framework

۳٫ Methods

۴٫ Results & discussion

۵٫ Conclusion

Acknowledgements

Appendix A. Supplementary data

References

Abstract

Nature-based Solutions (NBS) are increasingly promoted to support sustainable and resilient urban planning. However, design and planning urban NBS targeted at the needs of the local context require knowledge about the causal relationships between NBS, ecosystem services (ES) and urban challenges (UC) This paper aims at contributing to this knowledge, by systematically identifying nexuses (i.e. qualitative links) between UC, ES and NBS, and describing plausible causal relationships. A conceptual UC-ES-NBS criteria framework was built, and used to guide a two-step systematic literature review on current UC and on the supply of ES by urban NBS. This was followed by a non-systematic literature review, which complemented the previous one by unveiling knowledge gaps on the biophysical and social processes and attributes on which specific ES classes depend. The non-systematic review was also used to identify additional NBS. The UC review identified 18 UC and 58 sub-challenges, and illustrated which UC were more studied, according to the type of literature and environmental and socio-economic attributes of urban contexts. The ES review led to the development of an urban NBS classification, and supported the identification of UC-ES and ES-NBS nexuses, which were analysed and classified into four groups of causal relationship. For the nexuses identified as direct plausible causal relationship, the main processes and attributes on which the supply of specific ES depend were pointed out. Relationships between UC, ES, NBS, processes, and attributes were represented in the form of network diagrams. Our results can be used to support urban policies aimed at mainstreaming NBS and as a basis to further understand UC-ES-NBS relationships.

Introduction

heir associated environmental impacts are expected to continue over the coming decades (Keivani, 2009). These trends are likely to intensify existing urban challenges (UC) for sustainability and resilience, as well as generate new ones. In terms of sustainability, UC include all factors that limit the capacity of urban areas to protect and conserve the environment, minimise environmental impacts and enhance resource-efficiency, human health, social inclusiveness and equality, as well as harness the productivity of local economies and value-added activities (United Nations, 2017). In terms of resilience, UC relate to those factors that limit the capacity of urban areas (including their inhabitants, institutions and inner systems) to resist and adapt to environmental, social or economic chronic stresses, and acute shocks (Meerow et al., 2016; Marron Institute of Urban Management, 2018). In many cases, UC for sustainability and UC for resilience (hereafter referred generically to as UC) overlap and also share limiting factors. The nature of these limiting factors, can be biophysical (e.g. a lack of woody vegetation can contribute to the presence of heat islands), technological (e.g. insufficient technological development for achieving universal access to certain goods or services), human-social (e.g. the current human, institutional or social structure act as barriers for adapting to new situations), and/or financial (e.g. limited amount of money restricts access to products of a certain quality). UC can therefore be determined by many types of limiting factor, which need to be understood before strategies and interventions can be developed to mitigate or address those UC.