Investing in Urban Green Space, Investing in Health

[This article was published in Catalan in Espai Salut, a bulletin published by the Diputació de Barcelona]

Today, in an ever more urbanised world, the challenges of sustainable development increasingly affect—and will continue to be concentrated in—cities, which will be home to 75% of the world’s population by 2050.

The problems associated with city life—air and noise pollution, poor urban design, extreme temperatures, etc.—are closely linked to climate change and will remain the focus of attention in the public-health sphere. Recent research has demonstrated the direct and indirect benefits of green space in cities.

Recent research has demonstrated the direct and indirect benefits of green space in cities

Various studies have shown that urban green space reduces stress and improves the physical and mental well-being of people who are exposed to it. Other studies have shown that greater exposure to urban green space is associated with a lower rate of mental health problems and conditions (e.g. depression), beneficial effects on brain development in children, and slower cognitive decline in elderly people.

As well as having a beneficial effect on stress, some species of tree also trap air pollutants, a phenomenon that may go some way to explain the mental and cognitive health benefits observed in study participants.

A recent study of nearly 3,000 schoolchildren at 39 schools in Barcelona, which took various socioeconomic factors into account, found that children who attended schools located close to green spaces scored higher on working-memory tests than their counterparts at schools with less surrounding greenness. Moreover, over the course of a year the differences in working memory between the two groups became more pronounced. The same study found that students from greener schools had fewer attention problems. The researchers determined that part of the observed effect—between 20% and 65%—could be attributed to lower levels of air pollution around the schools located close to green spaces.

Urban Green Space for Cleaner Air

Urban green space helps to reduce levels of air pollution through a process known as dry deposition, which occurs when airborne particles settle on a surface. This process reduces levels of particulate matter in the air. A study carried out in the United States estimated that urban trees in 55 cities removed 711,000 tonnes of air pollution per year, a service valued at $3.8 billion.

The fact that exposure to green space reduces stress levels, air pollution and noise (trees and shrubs are often used as sound barriers, especially in noisy areas) could also explain the association between greenness and mortality observed in various studies. A paper that combined the findings of several studies observed that the likelihood of premature death—that is, a death occurring before the average age at death in a given population—was 4% higher in populations with lower exposure to greenness. The results were especially consistent when the researchers specifically considered premature mortality associated with cardiovascular disease, a condition in which stress, air pollution and noise all play a major role.

A paper that combined the findings of several studies observed that the likelihood of premature death was 4% higher in populations with lower exposure to greenness

Vegetation Against Climate Change

Increasing green space in cities is also a key strategy for reducing the impact of climate change and heat islands. A heat island is an urban area that experiences higher temperatures than the surrounding natural areas. The effect is caused by high building density and, in particular, by the heat-absorbent materials used to construct cities: cement, asphalt, and even the rubber surfacing used in playgrounds and tree pits.

Studies have found night-time temperature differences of up to 12ºC between urban areas and periurban natural areas. Urban green space may play a significant role in efforts to adapt to climate change as summer heat waves are expected to become more severe and more frequent with continuing global warming.

City planners should therefore take into account the shade and water vapour (from evaporation) provided by urban green spaces. A study from 2016 quantified the benefits of trees in 245 cities all over the world and found that mortality associated with high temperatures would decrease by between 2.4% and 5.6% if the maximum possible number of trees were planted on city streets. The presence of the trees would also reduce electricity consumption and increase carbon dioxide absorption.

Maximising the Effects of Trees

To obtain maximum benefits from urban green space, city planners should note that proximity to people is a key factor in the effectiveness of trees in reducing temperatures and levels of particulate matter. We know that trees are most effective when they are located less than 300 metres from people (or residential areas, schools, etc.). Trees must also be healthy and well maintained to ensure the greatest possible reduction of pollution and temperature.

City planners should note that proximity to people is a key factor in the effectiveness of trees in reducing temperatures and levels of particulate matter

For inspiration, check out these videos to get some ideas about how we can make our cities healthier and more sustainable:

• “Climate: Nature-Based Solutions for Climate Change Mitigation and Adaptation in the Paris Region”
• “Urbanism, Architecture and Biodiversity: When Nature Inspires Cities and Buildings”

And here is an interesting link: “Urban Green Spaces and Health – A Review of Evidence” (World Health Organisation, 2016)