Urban green space
In land-use planning, urban green spaces are open-space areas reserved for parks and other spaces of greenery. These include plant life, water features also known as blue spaces and other kinds of natural environments. Most urban open spaces are green spaces, though some may consist of other types of open areas. The landscape of urban open spaces can range from playing fields and other highly maintained environments to more natural landscapes that appear less managed.
Urban green spaces may also include areas that are not publicly accessible, such as privately owned higher education campuses, school sports fields, allotments, neighborhood or community parks and gardens, and corporate campuses. Areas outside city boundaries, such as state and national parks or rural open spaces, are not generally considered urban open spaces. Boulevards, piazzas, plazas, and urban squares are not consistently classified as urban open spaces in land-use planning.
Urban greening policies help revitalize communities, reduce financial burdens on healthcare, and improve quality of life. By promoting the development of parks, green roofs, and community gardens, these policies contribute to cleaner air, mitigate urban heat effects, and create spaces for recreation and social interaction. Most policies focus on community benefits and reducing negative effects of urban development, such as surface runoff and the urban heat island effect. Historically, access to urban green space has favored wealthier and more privileged communities. Recent urban greening has increasingly focused on environmental justice concerns and community engagement in the greening process. In particular, in cities with economic decline, such as in the Rust Belt in the United States, urban greening has broad community revitalization impacts. Urban green spaces have been shown to have a wide-reaching positive impact on the health of individuals and communities near said green space.
Definitions and concepts
The World Health Organization defined urban green spaces as "all urban land covered by vegetation of any kind". In academic literature, "urban open space" or "open space" is often used to describe a broader range of open areas. One extensive definition describes open space as follows:"Thus open space, very simply, is unclosed space. As the counterpart to development, urban open space is a natural and cultural resource, synonymous with neither "unused land" nor "park and recreation areas." Open space is land and/or water area with its surface open to the sky, consciously acquired or publicly regulated to serve conservation and urban shaping functions in addition to providing recreational opportunities.In almost all instances, the terms urban green space or urban open and green space refer to open areas that reflect natural areas surrounding the city.
Public spaces are broadly construed, including meeting or gathering places that exist outside the home and workplace. These foster resident interaction and opportunities for contact and proximity. This definition implies a higher level of community interaction and places a focus on public involvement rather than public ownership or stewardship.
Benefits
The benefits that urban open spaces provide to citizens can be categorized into four basic forms: recreation, ecology, aesthetic value, and positive health impacts. Psychological research shows that benefits to visitors of urban green spaces increased with their biodiversity, indicating that "green" alone is not sufficient: the quality and variety of the urban green space are important as well.Recreational
Urban open space is often held in esteem for the recreational opportunities it provides. Examples of recreation in urban open spaces include active recreation and passive recreation. Research shows that when open spaces are attractive and accessible people are more likely to engage in physical activity. Time spent in an urban open space for recreation offers a reprieve from the urban environment and a break from over-stimulation. Studies on physically active adults, middle-aged and older, show that there are amplified benefits when physical activities are coupled with green space environments. Such coupling leads to decreased levels of stress, lowers the risk of depression, and increases the frequency of participation in exercise.Ecological
Green spaces may improve the air quality of urban areas and provide habitat for wildlife, improving the overall ecological health of urban environments. They may also reduce the risk of flooding by providing rainwater drainage.Aesthetic
Urban spaces also hold a certain aesthetic value. People enjoy viewing nature, especially when it is otherwise scarce, as is the case in urban environments. Therefore, open space offers the value of "substituting gray infrastructure." One researcher notes how attractive neighborhoods contribute to positive attitudes and social norms that encourage walking and community values. Properties near urban open spaces tend to have a higher value. One study was able to demonstrate that, "a pleasant view can lead to a considerable increase in house price, particularly if the house overlooks water or open space." Certain benefits may be derived from exposure to virtual versions of the natural environment, too. For example, people who were shown pictures of scenic, natural environments had increased brain activity in the region associated with recalling happy memories, compared to people that were shown pictures of urban landscapes.Impact on health
The World Health Organization considers urban green spaces as important to human mental and physical health. Urban open spaces often include trees or other shrubbery that contribute to moderating temperatures and decreasing air pollution. Perceived general health is higher in populations with a higher percentage of green space in their environments. Urban open space access has also been directly related to reductions in the prevalence and severity of chronic diseases resulting from sedentary lifestyles, improvements in mental well-being, reduction in gun violence, and reductions in population-wide health impacts from climate change.Mechanism of urban open space health effects
Access to urban open space encourages physical activity and reduces ambient air pollution, heat, traffic noise, and emissions. All are factors which contribute to the risks of chronic disease and mental illness. Individuals and families who lived closer to 'formal' parks or open space were more likely to achieve recommended amounts of physical activity. Urban open space has also been attributed to providing cleaner air quality, thus reducing rates of chronic respiratory diseases among the surrounding population. Urban open space can provide venues for outdoor physical activity which can increase lung function and be a protective factor against respiratory disease. These spaces also offer exposure to nature, which has been proven to boost the immune system by introducing microorganisms to the human body through contact with soil, turf, or forest floor.Reductions in chronic disease rates
Improved access to green space is associated with reductions in cardiovascular disease symptoms, improved rates of physical activity, lower incidence of obesity, and improved respiratory health. Lower rates of cardiovascular biomarkers are associated with access to green space, showing a reduction in cardiovascular disease risk in populations living within 1 km of green space. Not only does access to urban green space reduce risk of cardiovascular disease, but increased access has been shown to improve recovery from major adverse cardiovascular events and lower all-cause mortality. Relationships have been found between increased access to green space, improved rates of physical activity, and reduced BMI. The percentage of sedentary and moderately active persons making use of an urban park increased when access to the park was improved.Reductions in mental illness rates and improvement of social cohesion
Globally, mental illness is linked to eight million deaths each year. In urban areas, limited access to green space and poor quality of green spaces available may contribute to poor mental health outcomes; according to some studies, people living in cities and towns may have weaker mental health in comparison to people living in less crowded areas. Urban green spaces are pieces of nature in the cities designed to address this problem. The distance an individual lives from a green space or park and the proportion of land designated as open space/parks have been shown to be inversely related to the number of anxiety/mood disorder treatments in the community. Improved mental health may therefore be related to both measures – to distance from open space and proportion of open space within a neighborhood. Even when physical activity rates do not increase with greater access to green space, greater access to green space decreases stress and improves social cohesion.Effects on respiratory health
Adequate urban green space access can be associated with better respiratory health outcomes, as long as green space areas meet certain requirements. A study showed that mortality due to pneumonia and chronic lower respiratory diseases could be reduced by minimizing fragmentation of green spaces and increasing the largest patch percentage of green space. Vegetation type and lack of management has been shown to affect a higher capacity to provide the ecosystem services of air purification and climate regulation within green urban spaces. The types of plants and shrubs are important because areas with large tree canopies can contribute to asthma and allergic sensitization.Impacts on high temperatures
Urban areas tend to have higher temperatures than their surrounding undeveloped areas because of urban heat islands. Urban heat islands are areas with man-made infrastructure that contribute to increased temperatures. The average temperature during the day in cities can be 18–27 degrees Fahrenheit higher than in the surrounding rural regions. This is an example of surface heat islands, a type of UHI, which encompass the area from the ground to the top of the tree-line or mean roof height. It is usually higher during the day when direct sunlight reaches urban structures, particularly pavement. The other type of UHI, atmospheric heat islands, reach from above the tree-line or mean roof height to the level in the atmosphere where the urban area no longer has an effect. This type of heat island has increased heat at night due to the release of heat from infrastructure that built up throughout the day.Green spaces within urban areas can help reduce these increased temperatures through shading and evapotranspiration. Shading comes from the taller plants, such as trees, that can contribute to lowering the surface heat island effect. The shade provides protection from the sun for vulnerable populations, such as children, during periods of increased temperature, during the summer months or during a heat wave. Tree cover prevents some solar radiation from reaching the ground with its leaves and branches. This reduces the effect of surface urban heat islands. Open spaces that include any type of vegetation help offset the high temperatures through the natural process of transpiration. Transpiration releases water vapor into the air from within plant leaves, absorbing heat in the evaporation process. There are many elements of an urban open space that can contribute to the mitigation of urban heat islands including the type of open space, type of plant species, and the density of vegetation. Green spaces contribute to the reduction of local heat, decreasing the overall effect of UHIs. The larger the distribution of green spaces, the bigger the area of heat reduction. Green spaces that are clustered together will have an additive heat reduction resulting in a greater decrease in temperature in the local area compared to surrounding areas.