Park, J., J. Kim, D.K. Lee, C.Y. Park, S.G. Jeong. 2017. The influence of small green space type and structure at the street level on urban heat island mitigation. Urban Forestry & Urban Greening (21): 203-212.
Green spaces in cities are something we all love and, especially during lockdown, are a great way for city dwellers to feel connected with nature. Whether it’s spending time in a park with friends, sitting under the shade of a big tree, or enjoying flowers alongside the road, plants are a key component to a beautiful cityscape. In addition to adding beauty to city streets, vegetation and green space provide important services to city dwellers, including taking up carbon dioxide, giving us oxygen, and helping to cool the temperatures.
A team of researchers in Seoul, South Korea, led by Dr. Jonghoon Park, wanted to better understand the types and structures of green spaces in cities that were the most effective at cooling the surrounding air on a city block. Urbanization, or a move towards city living, has been increasing worldwide since the 1960s and it is expected that by 2030, 81% of the world’s population will live in urban areas. This rapid movement to the city has come with increased development, land cover change, and pollution – all of which contribute to warming temperatures and climate change. Scientists have expressed concern about this phenomenon for many years, and recently decision-makers and urban planners have begun incorporating climate change mitigation and adaptation practices into the design of cities. One popular practice is the inclusion of vegetation and green spaces throughout urban areas.
Urban Heat Island
In cities, a phenomenon called the urban heat island effect is very common. The urban heat island (UHI) refers to higher temperatures in urban centers, as compared to nearby rural areas, due to the increase in paved surfaces and the lack of vegetation in cities. Urban dwellers in areas affected by UHI can experience damaging health effects due to the increased heat. Green spaces can help to mitigate these negative effects by creating cooling buffer zones, or “urban areas shaded by green spaces [that] are cooler than other areas heated by direct solar radiation” (Park et al. 2017).
The authors of this paper aimed to build on existing literature and explored the structure of urban green spaces and the effectiveness of different densities and green space structures at mitigating UHI. With only a few studies focusing on the density, size, shape, and ratio of green spaces, the authors hoped to fill the gap in the knowledge by examining the cooling effects of small green spaces at the street level. The authors’ study analyzed the cooling effects of six types of green space structures on highly developed city blocks in Seoul and measured the daytime air temperature on clear days through August and September of 2012 for a total of 12 days. The volume and area of each small green space was calculated. Three of the city blocks were used as controls and the other three had varying green space ratios and structures. Green space structures were defined based on the vegetation structures and shape of the individual green spaces.
Results from this study showed that UHI mitigation was most successful when the area and volume of the green space increased. The degree of cooling on an urban block was consistent with the size of the green space and the characteristics of the vegetation. Green spaces with depth and multiple layers and heights of vegetation (such as tall trees, shrubs, and ground cover species) performed the best at mitigating UHI and cooling the city block, as opposed to green spaces comprised of a single line of tall trees. In essence, green spaces can help reduce the urban heat island effect and cool temperatures in cities.
City Planning Implications
The authors of this paper hope that their results will be useful for urban planners looking to incorporate some of the benefits of green space into their urban areas. The results from this paper concluded that small green spaces could have a significant part in mitigating UHI at the urban blocks level, if constructed and planted correctly. Their results demonstrate how to optimize the cooling effects of green space in cities and give insight into how these green spaces should be designed and distributed to be the most beneficial to city dwellers. Next time you see green space in your city, think about how it’s working to serve you!