The available evidence indicates that urban green infrastructure (urban parks, street trees, green roofs and walls, etc.) can make a modest contribution to remedying carbon emissions, reducing heat stress and lowering atmospheric pollution in cities. If we wish to solve these problems, we need to take action on pollution sources because compensatory measures based on nature are far from sufficient. Urban green infrastructure strategies can play a role by complementing, but not replacing, pollution reduction strategies.
Urban green infrastructure can contribute to site-scale strategies to improve air quality and thermal comfort, and hence human health. Thus, for example, urban parks, street trees or green roofs or walls (vegetation on buildings) can act as clean air or cool areas and corridors within cities. The potential of green roofs, green walls and street trees is particularly relevant due to the lack of available land in urban cores.
The benefits and limitations related to urban green infrastructure should be considered in planning and management in order to estimate net contributions to environmental quality. Even if most urban green infrastructure elements are multi-functional in relation to the three ecosystem services considered in this analysis, some potential problems have been also identified. Thus, for example, street trees provide a high shading effect, but they are also associated with a potential “barrier effect” by which they prevent the dispersion of pollutants into the air.
Therefore, planning and managing urban green infrastructure within the context of its contribution to climate change mitigation and adaptation requires a holistic approach. Planners and policy-makers must take into consideration the whole range of ecosystem services provided by different types of urban green infrastructure and the interactions between them, together with the different spatial scales at which these ecosystem services can be significant. This approach calls for strong multi-scale institutional coordination between all the authorities dealing with urban and environmental policies and for the harmonization of planning and management instruments across different sectors.
Watch a video titled “Ecosystem services in cities: key pathways between green space and human health?” by Dr. Francesc Baró, postdoctoral researcher at the Laboratory for Urban Environmental Justice and Sustainability (ICTA-UAB and IMIM):