In terms of climate resilience, green corridors contribute climate mitigation. They reduce the GHG emissions, due to modal shift and the carbon sequestration with vegetation. Green corridor contribute to climate adaptation, by reducing car use which causes heat rejection and aggravates the heat island.

In terms of health, they improve air quality and reduce noise pollution. They can affortable and contribute to equity in transport. They offer improved land use thanks to their small land footprint. They reduce road danger and contribute to overall well-being through enhancing attractiveness of cities and offering opportunities for healthier lifestyles. 

Lastly, in terms of biodiversity, they can be part of ecological networks thus contribute to urban biodiversity.

Green corridors essentially comprise a linear route, street, pathway infrastructure, which use a series of street trees, swales, rain gardens, and pervious pavement to create a cooler oasis and promote active and sustainable mobility, whether this is walking, cycling or micro-mobility.

Green corridors can vary significantly in terms of length and use of green materials in their design. The selection of the site where to implement a green corridor largely depends on the urban form, layout of the city and availability of land. Nevertheless, in principle they could be implemented in all neighbourhoods of a city, particularly in the areas which have the lowest score in terms of green areas and permeable surfaces. In particular, green corridors promote alternative mobility means which do not make use of the car. In this sense, they are open, public and affordable, are associated with lower emissions and, hence, promoting equity and accessibility for people with reduced mobility.

The choice of which nature-based solutions to adopt in designing green corridors largely depends on local climatic and geographic conditions, making these technical specifications inevitably contextual. While green corridors do not necessarily need policy or regulatory framework to be implemented, they usually require funding to be implemented by the public authority.

Technical:

Land availability, existing infrastructure and land-use compatibilities can represent a potential obstacle to implementing green corridors. This is particularly true for those urban contexts where car ownership and car dependence are still very high, due to a not efficient public transport and the lack of alternative mobility means. Moreover, cities might face resistance from citizens, communities and groups, who are (at least initially) against pedestrianization or unwilling to receive restrictions on the use of the car. In this regard, early civic engagement is crucial for the successful implementation of green corridors, as witnessed for instance in the case of Passeig de Saint Joan in Barcelona.

Socio-economic:

Green corridors are generally considered to foster equity, as they promote alternative mobility means and create healthier public spaces. However, large green corridors might affect the land value of specific plots and neighbourhoods, leading to uncontrolled or undesired green gentrification.

Furthermore, another issue is the maintenance of green corridors, which requires adequate financial resources, and it this is usually done by the municipality or a public authority – either directly or through contracting. Citizens could be directly involved in planting trees and in the maintenance, as already experimented in cities such as Milan and Belfast (projects ForestaMi and 1 Million Trees respectively).

Although undesired or unexpected, some drawbacks or adverse impact might happen after the implementation. For instance, the implementation of a large green corridor with stringent car traffic limitation might alleviate car congestion in one neighbourhood but could have opposite effects on other roads and districts of the city.

Other potential drawbacks are related to conflicting interests and alternative land use. For example, the city of Stuttgart implemented a large, city-wide scale strategy of green corridors, experiencing conflicts in competing interests and trade-offs, with loss of potential tax revenues from constructions and high housing costs.

• Sustainable Urban Mobility Plans (SUMPs) and Cycling: Guide (EC)

Green corridors provide several co-benefits, not only from an environmental point of view. In terms of climate resilience, they contribute to both mitigation and adaptation (thanks to the modal shift from car and carbon sequestration though nature-based solutions). They also foster cooler urban environment, mitigating the impact of extreme heat events and the urban heat island effects in neighbourhoods, and enhance biodiversity thanks to their function as ecological connectors.

Green corridors also provide benefits for health and well-being, thanks to improved air quality, noise reduction, active lifestyle and street safety (thanks to the limitation in the use of the car). The impact of a green corridor largely depends on its scale, design and green materials used. Once designed, a green corridor becomes part of the urban context and it is difficult to monitor it.

A number of indicators could be used to capture the co-benefits achieved. For instance, estimating the carbon reduction potential based on the numbers of trees planted, monitoring improvements in ecological biodiversity, and measuring temperature to assess the localized cooling effect of vegetation, but also use of green corridors and social acceptance/satisfaction.

Green corridors are consistent with the DNSH principles for environmental objectives, especially for climate change mitigation and adaptation, pollution prevention and control, protection and restoration of biodiversity.

Indicative KPIs to be defined in more detail per study area:

• KPI1: Area covered by green space
• KPI2: Temperature regulation against baseline
• KPI3: Increased number of users of corridors (including segments, e.g. age, gender)
• KPI4: corridor connectivity index
• KPI5: biodiversity increase
• KPI6: Air quality (PM10 and 2.5 concentration)

There are different options to promote and mainstream the implementation of green corridors within cities.

On the strategic level, they could be included as potential interventions under the city’s Climate Action Plan or Resilience Strategy; on the operative level, the design and specification of green corridors might be integrated into land-use plans and zoning plan (e.g. low emission zones). In particular, the implementation of green corridors should also be reflected in the city’s Sustainable Urban Mobility Plan, considering how these could contribute to the re-design and functional re-organization of mobility infrastructure in the city. In any case, an integrated approach is needed, linking planning, land-use and mobility. For instance, the city of Lisbon implemented a series of green corridors under the Master Development Plan and Biodiversity Action Plan. 

Other tools such as Green Infrastructure Mapping could be used to identify neighbourhoods where green spaces are lacking or fragmented, and where green corridors could be implemented. Educational activities and monitoring tools could also be important to promote citizens’ engagement, raise awareness about co-benefits, and foster acceptability.

• Barcelona: green corridor (NATURVATION project)

In 2020 the city of Barcelona launched the Barcelona Green Infrastructure and Biodiversity Plan 2020, including the development of several urban green corridors to increase ecological and social connectivity within the city. The green corridor of Passeig de Sant Joan is one of the first of these corridors implemented.

The city of Stuttgart implemented a green corridors strategy to create a green infrastructure network, mitigate extreme heat events, and improve air quality. One of the main success factors was that the city institutionalized the integration of urban climatic concerns into planning (i.e., cold air regime, ventilation corridors).

The city of Lisbon implemented a series of green corridors under the Master Development Plan and Biodiversity Action Plan. The Main Green Corridor, a 2.3 km long green corridor connecting is considered as the city’s largest green infrastructure, crossed by pedestrian/cycle paths.