An urban heat island is where the built up area is warmer than the surrounding rural areas. In simple terms human activity creates this by building surfaces that soak up the heat (solar radiation) in the day and slowly releases that heat in the night. Urban areas have less green space and trees as well, so evapotranspiration is also significantly less in urban environments. Less vegetation means less natural shading and also means less trees to help deal with carbon emissions.
Tall buildings also create urban canyon effects, which means they contribute to the reflection and absorption of sunlight which contributes to the phenomenon. All of these things, when combined, contribute to the overall effect. The effects of heat islands are complex and wide, but the key of which this blog is concerned is the effect on health. They can contribute directly to heatwaves, and this is a killer once temperatures reach certain levels, especially for the older generation (*). Increased temperatures also contribute towards heat strokes, heat exhaustion and heat cramps (**). A solution that is currently being promoted globally is cool surfaces. The advantage of this is it is simple solution and cost effective. This is about increasing the albedo, or solar reflectance of surfaces to mitigate the problem. Existing technologies can increase urban surface albedo by 10% (***). By having something as simple as white roofs can have a huge benefit and is a cost efficient and easy methodology that can be used everywhere. Another area that can help mitigate the issue is the use of green space within urban environments. Trees are crucial to this as they provide shading and soak up carbon emissions and also contribute to cooling the environment through evapotranspiration. Many cities fully understand this, not only for cooling but also for aesthetic reasons associated with mental health. 202020vision is an organisation in Australia that is promoting the increase of green space within Australia by 20% by 2020 (****). It is focussing on 28 projects across the country and to date has over 400 organisations signed up. Our cities are predicted to continue to grow in size, and the overall world population is predicted to see a higher percentage growth of people living in urban environments so it is crucial that technology and design incorporate the principles of cool surfaces going forward, as they will be an important facet of the overall sustainability goals needed for urban environments of the future. This, tied in with more thought towards the use of green space, can have a significant beneficial effect on the effects of the Urban Heat Island globally (*) R. W. Buechley; J. Van Bruggen & L. E. Trippi (1972). "Heat island = death island?". Environmental Research. 5 (1): 85–92 (**) Kovats, R. Sari; Hajat, Shakoor (April 2008). "Heat Stress and Public Health: A Critical Review". Annual Review of Public Health. 29 (1): 41–55 (***) Akbari H, Menon S, Rosenfeld A. 2009. Global cooling: increasing world-wide urban albedos to offset CO2. Climatic Change, 94 (3-4), 275-286. (****) 202020vision.com.au
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AuthorGerald Walker. BA Hons Economics and Studying for a Masters at UNSW in Property and Development Archives
June 2017
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