How do green spaces lower temperature in cities?

Green space or the open natural environments in the cities are the lungs of the cities. It can be in the form of  public parks or private campuses and community/institutional parks/gardens. State and national parks or open country spaces on the periphery are not urban green spaces as their benefits for the city are limited.

The benefits of urban green spaces are unlimited. Man's bond with nature is ancient. Nature is a source of inspiration and relaxation for humanity. People living in stressed, congested city environments often long for the countryside natural environment. The individuals and communities near green spaces receive valuable positive benefits, which may be in the form of pure air, better physical or mental health, recreation and much more. However, these benefits are not only limited for humans but the city environment also benefits from these green spaces.

Role of green spaces in reducing the temperature of the cities is widely accepted. Concrete city structures get heated up quickly during day time and release heat during night. Due to this, the average temperature in cities can be 1-3 degrees celsius higher than in the surrounding rural regions. This results in the formation of  Urban Heat Islands, or UHIs. If we try to visualize the temperature profile of urban and surrounding rural regions graphically and spatially, it will show an island of higher temperature than surroundings. Thus it is named as urban heat islands. The concrete structures in the cities are mainly responsible for the heat island effect. The pollution from the automobile and industry releases carbon dioxide. CO2 is a known greenhouse gas which increases temperature of the cities.

Green spaces within urban areas can restrict the direct heating of the concrete pavements. The tree canopy reduces the incoming solar radiation through shading.  The process of evapotranspiration reduces heat by releasing water into the air. Some factors like type of  green space (park or nature reserve), type of plant species, and the density of vegetation also plays an important role. For instance, trees with broad canopy like banyan or peepal trees, provide shade in a larger area and are more effective in reducing heat. Thus, green spaces decrease the overall effect of UHIs. The larger the green spaces in the city, the smaller will be the heated areas. Clustered green spaces are more effective in reducing temperature. Green spaces are also helpful in reducing pollution by absorbing carbon dioxide and releasing oxygen. This green space works in many ways in reducing the temperature of the cities.