Urban green infrastructure planning and nature-based solutions

Participatory approaches are needed in urban green infrastructure planning and in the design, implementation and assessment processes of NbS. Engaging with different stakeholders enhances knowledge transfer between actors, while addressing potential social or institutional barriers is crucial to enhancing societal acceptance of these solutions and finding the best option that takes local socio-political context into account. Especially local and regional authorities have a great role and therefore strong horizontal and vertical cooperation is required, but also the link to the private sector is important. 

Managing the urban landscape is a complex process subject to conflicting agendas such as housing, transport, commercial infrastructure, and economy. Urban green infrastructure needs comprehensive planning and maintenance. Establishing a city-wide green space network with connected corridors needs to be weighed and valued as one key land use type together with other key land use sectors. Competing and conflicting land use interests, weak collaboration with key stakeholders (e.g. land-owners, building sector, investors) or silo-thinking in city administration can act as strong limiting factors. Lack of knowledge on benefits, or experience in how to implement or design NbS can cause negative attitudes among practitioners, policy-makers or citizens.  

The local environmental, social, cultural and institutional context greatly impact the success of UGI planning and implementation of specific NbS. Therefore, evidence-based standards and guidelines have been developed for cities to ensure effective and participative UGI planning and governance of different NbS, for example in several EU funded projects (e.g. GREEN SURGE ,ThinkNature, Naturvation). In addition, integrative and inclusive governance approaches such as “mosaic” governance (combining the micro-level of active citizenship with the macro-level of strategic urban planning, Buijs et al., 2019) are good ways to promote socially cohesive and collaborative UGI planning, implementation and maintenance.

The loss of green spaces, degradation of natural ecosystem, densification of city structure and increasing proportion of paved soil have negative impacts on the water cycle, air quality, local temperature and decrease the climate resilience of cities. These have great economic costs for the society and greening of cities (e.g. planting trees or establishing new green space), restoration of degraded ecosystems, choosing low-intensive management practices in parks, or constructing local nature-based solutions can bring significant direct savings to control run-off water or flooding compared to traditional engineered-based solutions .In addition, these green actions also have many indirect economic benefits e.g. by attracting investors, tourism and creating new jobs for a variety of sectors. 

The cost of UGI planning and implementation of NbS can vary greatly depending on many internal factors such as spatial scale, the use of technology in solutions, frequency of maintenance and need for repair. Usually, maintenance costs are lowest in natural ecosystems such as remnant habitats (e.g. urban forests or wetlands) or semi-natural ecosystems (e.g. replacing lawns with meadows). Establishment and maintenance costs of some types of NbS are partly or entirely covered by citizens (e.g. urban farming), NGOs (e.g. restoration actions of degraded habitats) or private businesses (stormwater ponds for managing run-off water). The European Union has put great effort into mobilising NbS in Europe by offering financial support through the European Green Deal, strengthening knowledge transfer about successful cases (e.g. Urban Nature Atlas) and offering public digital platforms to encourage collaboration with private and public sectors (The Smart Cities Marketplace). 

Green spaces and NbS in cities can contribute to multiple benefits, including enhancing human health and climate resilience of cities. They reduce disaster risk, improve water management and produce local cooling effects to better cope with high temperatures and heatwaves. Other co-benefits include: supporting urban biodiversity, carbon storage (mitigation), mitigation of air pollution, offering spaces for recreation, nature experience and providing increased social, physical and mental wellbeing. NbS in urban areas can contribute to several Sustainable Development Goals (SDGs), and especially to the targets on sustainable cities (11). 

In many EU Member States urban green infrastructure and nature-based solutions have already been supported by national legislation related to land-use planning, stormwater magement, surface water or biodiversity protection. There have been incentives and payments developed that encourage the implementation of NbS and UGI instead of traditional grey infrastructure. In addition, specific planning tools such as the Biotope Area Factor (see for example the Berlin case study) can be used in local zoning to require a proportion of the area to be left as green space. The European Union strongly supports the concept of green infrastructure and nature-based solutions in enhancing climate resilience, sustainable water management and well-being of humans and biodiversity in European cities. For example, UGI and NbS are seen as key concept in the: EU Biodiversity Strategy 2030 (2020), EU Strategy on Green Infrastructure (2013) and the EU Water Framework Directive. Finally, the 2021 EU Strategy on Adaptation to Climate Change stresses the importance of fostering nature-based solutions for adaptation, also through their upscaling at the urban level. 

Implementation time varies depending on spatial scale, from a few months to several years. For example, the implementation of small-scale NbS such as green walls or local biofilters is a rather fast process and actual construction time takes less than a year. However, planning and designing, getting official permissions, integration to other planning and development processes may lengthen the implementation time. Large scale green space planning and implementation (e.g. the development of a multifunctional park) may take several years. Technical implementation of novel green spaces is also shorter than the full ecological implementation. It may take several years before vegetation planted into green spaces or single NbS such as green roofs deliver their full ecosystem functions (e.g. climate mitigation or water and nutrient holding capacity). 

The expected life-time of interconnected urban green infrastructure should be very long, much longer than single buildings or grey infrastructure. The age of a single green space can vary from several hundreds of years (e.g. historical parks) to a few years (e.g. green roofs). The life-time of single NbS can also vary, but the aim is their long-term maintenance.