Expert article
Edit 23 June 2022
by Tamás Kállay

Urban green spaces are needed for public health

green space with people
Image: Ignacio Brosa, Unsplash
The CLAIRO project demonstrates the positive impact of urban greenery on air quality. Apart from reducing air pollution, urban vegetation provides a range of other health benefits. Having a two-hour ‘dose’ of nature every week can do a lot for our health and wellbeing according to research. Positive health benefits were found to peak around four hours of weekly nature exposure, but spending more than five hours has no further benefits. Interestingly the positive effects are the same if the weekly two hours are taken in shorter visits. Furthermore, for mental and physical health benefits, it is sufficient to simply sit on a bench and enjoy nature. There is also evidence that even small-scale greening interventions can deliver health benefits.

Living in an urban environment is taking a toll on our health and quality of life. According to the estimates of the World Health Organization (WHO) 63% of global mortality, about 36 million deaths annually, is due to chronic diseases. A large proportion of these deaths are associated with risks related to the urban built environment, such as physical inactivity and obesity, cardiovascular and respiratory diseases due to urban air pollution emitted from transportation, and heat-related strokes and illnesses.

A growing body of empirical evidence indicates that exposure to urban green spaces has positive impacts on both our physical and mental health. According to research people who spend more time in green spaces have significantly reduced risks for a number of chronic illnesses. Increased greenspace exposure was found to be associated with reduced blood pressure, lower heart rate, lower cholesterol, better pulmonary and immune function, reduced risk of stroke, cardiovascular disease, and asthma. Higher levels of green space were also found to positively correlate with lower levels of obesity. Furthermore, direct exposure to green space improves the functioning of the immune system. Just having a view of nature can provide physical benefits.

The quality of the green spaces is a relevant factor that influences health outcomes. The diversity of landscape features seems to have an important role in the delivery of health benefits. Evidence suggests that greater variability of neighbourhood greenness is linked to reduced risk of cardiovascular disease and stroke. The likelihood of hospitalization and of self-reported heart disease or stroke was lower among people who lived in urban areas with highly variable greenness.

Access to natural environments can also improve overall mental health. The impacts of green spaces to mental health include reduced stress levels, improved general mood, reduced depressive symptoms, better cognitive functioning, improved mindfulness and creativity.

One explanation to these beneficial effects of nature exposure can be that contact with natural environments or viewing natural elements, has a restorative effect that can be effective in reducing stress. These mental responses must be rooted in our evolution according to Wilson’s biophilia hypothesis, which argues that humans have an innate tendency to interact positively with nature.

Exposure to green space delivers health benefits through a great variety of pathways. Key pathways between nature and health include among others enhanced immune functioning, improved air quality, enhanced physical activity, stress reduction, greater social cohesion, reduction of the urban heat island effect and noise buffering.

According to the recommendations of the World Health Organization for health benefits urban residents should have access to public green spaces of minimum 0,5 hectares within 300 meters’ distance of their homes.

Green cooling islands and cooling corridors help mitigate heat stress

Parks and gardens, trees, green facades and roofs, can effectively reduce the heat in cities. Cooling by vegetation happens in various ways. When the sun radiation hit the trees' canopy it causes water to evaporate from the surface of leaves. During transpiration the leaves release water into the atmosphere which vaporizes and cools the surrounding air. Trees also provide cooling by shading. Moreover, green spaces influence the circulation of air in urban areas, that as a result can have an additional cooling effect on the micro-climate. Larger parks can also contribute to ventilation, generating an outflow of cool air from urban green spaces towards the surrounding built-up areas.

Medellin
Image: Mike Swigunski, Unsplash

 

Within parks, also relatively small ones, air temperature can be up to approximately 3 °C lower in comparison with the surrounding areas. In addition, green elements have a substantial positive influence on thermal comfort primarily because of the shading of tree canopies.

On the whole, a higher share of urban green spaces will increase the cooling potential of a city. Green parks can be particularly effective in reducing urban temperatures, as the cooling effect of parks extends beyond its boundary into the surrounding neighbourhood. Cooling corridors, such as tree-lined urban streets, can provide a cooling effect in densely built-in neighbourhoods. Squares can be converted into cooling islands if they are designed with more greenery, water and shading. Pocket parks, green roofs and green facades also have a cooling effect on their surroundings.

In extreme heat events, parks, school grounds, gardens and green patios of public buildings can all function as cooling elements for residents. Larger parks with water fountains are particularly effective as climate shelters. During heat waves park hours can be extended and public and private gardens that are normally closed to the public, can be made accessible for all.

 

Greenery can absorb, muffle and mask noise

Trees, hedgerows, open vegetation, green roofs and green walls can function as sound barriers. Vegetation reduces noise levels by several mechanisms. Sound is absorbed by plant parts such as leaves, stems, branches, and trunks. During sound deflection, the flexible material of plants is vibrating when it is hit by sound waves and audible energy is transformed into physical energy. Noise is also refracted by vegetation when sound waves bend around the soft structures of plants, similarly to a room where carpets and curtains dampen the noise.

traffic
Image: Alexander Popov, Unsplash

 

There is evidence that a dense belt of trees and shrubs can reduce sound levels by as much as 6 to 8 decibels, but low vegetation in open areas can also be effective as a muffling effect on sound, similarly to the carpeting in a room. What makes greenery as a noise buffer particularly effective is the fact that plants absorb sounds mainly at the highest frequencies that is perceived to be the most annoying.

Vegetation, apart from physically dampening noise, can also contribute to the perception of quietness. Noise bother people less, when they do not see its source. The use of green infrastructure between people and the source of noise impacts the human perception regardless of the thickness of the vegetation.

Natural sounds in green spaces, the rustling of leaves, the movement of branches in the wind, the sounds of birds and insects also have a noise masking effect. The sounds of nature have been associated with a range of perceived restorative experiences such as pleasure and relaxation.

Vegetation apart from physically dampening noise, can also contribute to the perception of quietness. Noise bother people less, when they do not see its source. The use of green infrastructure between people and the source of noise impacts the human perception regardless of the thickness of the vegetation.

 

Urban green spaces connect us with others and encourage physical activity

Urban green spaces have a relevant impact on residents’ wellbeing. The World Health Organisation defines health as ‘a state of complete physical, mental and social wellbeing and not merely the absence of disease or infirmity’. Accordingly social wellbeing is seen as a key component of health.

By providing a platform for community activities, urban green spaces encourage positive social interactions, improving social cohesion which in turn enhance health and wellbeing. Evidence indicates that people who connect with nature feel less isolated and form connections with others. Increased access to green space is also associated with reductions in crime, violence, aggression and anti-social behaviour.

community space
Park section functioning as a meeting place supporting social interactions

 

Research suggests that there is a positive link between the level of tree and grass cover in an outdoor space and the amount of social activity that takes place there. Almost twice as many individuals are engaged in social activities in green areas, compared to the sparsely vegetated ones.

Green spaces can provide an appropriate setting for performing various cultural activities, such as exhibitions, music, dance, public readings, plays and drama. Cultural programs are ideal tools for effectively attracting people to parks and thereby improve their wellbeing. Urban green spaces can be ideal locations for outdoor learning activities.

Availability of green space and greater levels of physical activity are strongly linked, as well as the associated health benefits. Evidence suggests that out of all the relevant factors, close access to the site is the most relevant one that contributes to increased physical activity in green space. People who are within walking distance of a park are more likely to use it and the recreation services provided at the site, than those who are not. Parks provide places for people to engage in physical activity. Large and attractive parks were found to promote walking for health benefits.

 

CLAIRO looks beyond air quality improvements

CLAIRO has a broad scope that encompasses more than the use of greenery for air quality improvements. The long-term goal of the project is to share the knowledge gained in Ostrava with other cities, and through this to enhance health and quality of life of citizens throughout the entire Silesian industrial agglomeration as well as in other Czech and European cities. Together with air quality, CLAIRO also addresses climate adaptation, the health and wellbeing of urban residents and the revitalization of cities.

The greenery design under CLAIRO aims at maximizing leaf surface to increase the pollution capture capacity of the new greenery, and this large surface can also reduce effectively local temperatures, and through this increase the thermal comfort of residents. Building on this effect on the microclimate, the impacts of the newly planted greenery on climate adaptation are also monitored in Ostrava.

The activities of CLAIRO are rolled out in the Upper Silesian metropolitan area and across Europe. For selected cities, recommendations were formulated on urban climate resilience and health-responsive development of green spaces, apart from air quality related greening measures. The CLAIRO study on behavioural changes published in 2021 urges cities to preserve and support greenery in pedestrian zones and around cycles paths to promote active transport and healthy lifestyles with the help of vegetation.

Both the National and the International Conferences of CLAIRO were embedded into a broader context linked to pathways from nature to health and wellbeing, addressing the reduction of urban heat stress, the design of high-quality green spaces, and the role of green roofs, green tram tracks, flower beds, or forest parks in developing a sustainable and healthy city.

 

As artificial urban environment is rapidly expanding, and as an ever-increasing proportion of the population is forced to live in cities, urban green spaces are becoming more and more valuable. Well planned and properly managed green spaces can significantly contribute to healthy urban living. As demonstrated above, a great variety of approaches can be taken by cities to link nature to health and wellbeing. Even small green space interventions, either physical changes or outdoor social activities can trigger massive changes, leading to improved health and wellbeing outcomes. Organizing facilitated green space activities is a particularly simple and inexpensive way to support health promotion.

 

Sources:

https://www.theguardian.com/environment/2019/jun/13/two-hour-dose-nature-weekly-boosts-health-study-finds

https://www.cnbc.com/2019/07/02/spending-2-hours-in-nature-per-week-can-make-you-happier-and-healthier.html

https://www.euro.who.int/__data/assets/pdf_file/0010/342289/Urban-Green-Spaces_EN_WHO_web3.pdf

https://www.who.int/initiatives/urban-health-initiative/health-impacts

Twohig-Bennett, C., Jones, A. (2018) The health benefits of the great outdoors: A systematic review and meta-analysis of greenspace exposure and health outcomes. Environmental Research. Volume 166, October 2018, Pages 628-637.

Bell, J. Wilson, J. and Liu, G. (2008). Neighbourhood greenness and 2 year changes in body mass index of children and youth. American Journal of Preventative Medicine, 35(6), 547-533.

Braubach M., Egorov A., Mudu P., Wolf T., Ward Thompson C., Martuzzi M. (2017) Effects of Urban Green Space on Environmental Health, Equity and Resilience. In: Kabisch N., Korn H., Stadler J., Bonn A. (eds) Nature-Based Solutions to Climate Change Adaptation in Urban Areas. Theory and Practice of Urban Sustainability Transitions. Springer, Cham. https://doi.org/10.1007/978-3-319-56091-5_11

Ulrich, R. S. (1981) Natural Versus Urban Scenes. Some Psychophysiological Effects. September 1981, Environment and Behavior, 13(5):523-556.

Pereira, G. et al. (2012) The association between neighborhood greenness and cardiovascular disease: an observational study. BMC Public Health volume 12, Article number: 466.

Kellert, S. R., and Wilson E. O., eds. The biophilia hypothesis. Island Press, 1993.

http://theconversation.com/can-trees-really-cool-our-cities-down-44099

Száraz, L. (2014) The Impact of Urban Green Spaces on Climate and Air Quality in Cities. ISSN 2052-0018 (print), ISSN 2053-3667 (online) Geographical Locality Studies 2014 Volume 2, Number 1. pp. 326–354.

van Dinther, D., Weijers, E., et al. (ECN) (2016) Designing green and blue infrastructure to support healthy urban living. ECN-O--16-029.

Wenqi, L., Ting, Y., Xiangqi, C., Weijia, W., Yue, Z. (2015) Calculating cooling extents of green parks using remote sensing: Method and test. Landscape and Urban Planning. Vol. 134, pp 66-75, ISSN 0169-2046, https://doi.org/10.1016/j.landurbplan.2014.10.012.

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