The way in which green spaces are incorporated into cities and urban spaces requires careful planning to make the best of the space without impeding development, and is unique to the issues and challenges faced by the individual city and its inhabitants. This article will discuss some of the primary methods of incorporating green spaces into urban planning and their key benefits.
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Green spaces in cities are beneficial to human health, both physical and mental, providing areas where people can partake in exercise and relaxation while also promoting benefits related to dissipated noise and chemical pollution. While urban spaces represent only around 2% of global land use, the majority of the population in developed countries live in them, around 80% in North America, 75% in Europe, and approximately 40% in Asia. Developing regions are rapidly closing the gap, however, and Asia is predicted to house around 60% of the world’s urban population by 2050. Concerningly, due to a lack of natural drainage and the presence of large flat paved areas, urban zones are more prone to flooding, which in association with enhanced intensity of precipitation in some regions associated with climate change, is causing more frequent and costly flood events.
How Do Green Spaces Combat Pollution?
Urban areas are associated with high carbon dioxide, volatile organic compounds, and particulate matter concentrations that are capable of impacting human health negatively, as well as the former contributing to global warming. In association, large surface areas of concrete and other building materials absorb and reflect heat back into the atmosphere, contributing to local warming and facilitating the formation of tropospheric ozone.
During photosynthesis, plants consume carbon dioxide and produce oxygen, then respire by consuming oxygen and producing carbon dioxide at night, though to a lesser extent. In any case, carbon dioxide levels spike significantly during peak traffic times in the day, and thus trees act as a carbon sink in the immediate environment. Further, particulate matter settles on the large surface area of trees, which are then washed by rain and renewed by growth. This acts to lessen the concentration of particulate matter in the air, which would otherwise be breathed in by humans or settle on buildings or other property.
Green spaces, in particular those with multiple trees and other large plants bearing foliage, are frequently utilized in noise reduction during urban planning and redevelopment. Environmental noise pollution is a significant issue in many urban areas, the vast majority typically originating from traffic. Trees absorb, reflect, and refract noise, largely via leaves acting as baffles to incoming sound waves, though also due to the trunk and branches acting as solid barriers. Noise reductions as high as 25%, amounting to 5 – 10 dB, are often reported following the planting of roadside trees, as measured from an objective distance.
Even greater noise prevention of 30 dB has been reported owing to the installation of vegetation facades and balcony trees, measured from inside of a building directly facing the road. Interestingly, factors such as tree density, tree height, tree clustering, trunk and branch dimensions, deciduousness, and even leaf shape affect the degree to which sound is absorbed or redirected and thus are considered during urban planning of green spaces.
How Can Green Spaces Be Introduced Into Urban Environments?
One method of introducing green spaces into dense urban zones is green roofs, wherein a garden is planted on the flat roof spaces of buildings. Typically, green roofs require the installation of a waterproofing membrane and drainage layer below the growth substrate, the thickness of which determines the types of vegetation that can be planted there. Substrates more shallow than around 15 cm can usually only support grasses and light shrubs, while deeper soils can support larger bushes and small trees.
It is important to note that the mass of soil increases rapidly with depth, and thus many buildings not designed with the capacity to bear significant weight are unable to accommodate an intensive green roof. Outside of acting as a carbon dioxide sink, green roofs offer other direct benefits to the building, such as improved insulation and enhanced water absorption.
Unique green roof designs incorporate water storage and grey water systems into the growth substrate, watering the vegetation and acting as a secondary overflow outlet. Many plants, such as hemp, are capable of phytoremediation, wherein they are used to collect and concentrate heavy metals and other pollutants, and thus could be incorporated into private or public roof gardens for the purpose of wastewater processing.
Community gardens provide agricultural and also social services to an area and can be planted in green roofs, parks, and other green spaces. The potential availability of garden produce such as fruits and vegetables at these sites provides significant social, economic, cultural, and educational benefits to an area, generally promoting investment by the community in the development of “participatory landscapes”.
Many issues with infrastructure could be solved by enhanced community efforts promoted by communal green spaces, such as blocked drains, fallen trees, and the reporting of damaged public property. Similarly, higher concentrations of people spending time outdoors in public green spaces would serve to reduce crime and promote community interaction, with associated benefits to health and the economy.
Green spaces are most severely lacking within industrial districts of cities, where economic incentives drive high building density and deter the construction of green spaces such as green roofs. Semeraro et al. suggest it is important to develop strategies that present an investment for the companies involved, bringing about community benefits for them and those around them. The study of urban planning and the optimum use of green spaces is highly interdisciplinary and will involve input from the environmental, physical, chemical, and agricultural sciences, amongst others.
Future urban planning activities are incorporating green spaces as a fundamental requirement during new projects to an increasing degree as their importance is realized, and similarly, many brown sites are being converted into community gardens and parks.
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References and Further Reading
Semeraro, T., Scarano, A., Buccolieri, R., Santino, A., & Aarrevaara, E. (2021). Planning of Urban Green Spaces: An Ecological Perspective on Human Benefits. Land, 10(2), 105. https://doi.org/10.3390/land10020105
Yan, A. et al. (2020). Phytoremediation: A Promising Approach for Revegetation of Heavy Metal-Polluted Land. Sec. Plant Biotechnology, 11. https://doi.org/10.3389/fpls.2020.00359
Margaritis, E., & Kang, J. (2017). Relationship between green space-related morphology and noise pollution. Ecological Indicators, 72, 921–933. https://doi.org/10.1016/j.ecolind.2016.09.03