What is it about?

Urbanization and the growth of cities has resulted in a phenomenon called the ‘urban heat island’ effect. In nature, plants and water bodies release extra absorbed heat back out through the transpiration and evaporation processes. But in cities, these natural bodies are replaced with buildings, pavements, and roads. These materials absorb and retain heat inside instead of expelling it. Elevated urban temperatures leads to an overuse of cooling devices like air conditioners. This leads to more energy spending consumption and high increased pollution. This effect is even more stronger pronounced against the backdrop of climate change and rising temperatures. The authors of the paper studied the effect of green roofs (vegetation cover) and cool roofs (reflective surfaces) on seasonal climate in urban areas. They studied 16 cities in the Yangtze River Delta metropolitan area. They found that green roofs lower temperatures by an increase the evaporation and transpiration rates, while cool roofs increase the reflection of the sun rays. Both options thus reduced the heat in the buildings during summer months. However, the downside of cool roofs was that they resulted in showed lower precipitation in summer and reduced temperatures in winter.

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Why is it important?

With rising temperatures and with the heat island effect becoming more common, it is important to find ways to lower the heat in cities without consuming a lot of energy or causing more pollution. Therefore, sustainable green strategies need to be used. The study outlines the usage of both the green roof and cool roof; considering the pros and cons of both is important when planning structures to tackle urban warming. KEY TAKEAWAY: Although both cool roofs and green roofs are effective in reducing summer temperatures, the latter has fewer adverse effects in other seasons. Therefore, there needs to be climate change policies with place-based solutions that look beyond summertime cooling only.

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This page is a summary of: Cool Roof and Green Roof Adoption in a Metropolitan Area: Climate Impacts during Summer and Winter, Environmental Science & Technology, August 2020, American Chemical Society (ACS), DOI: 10.1021/acs.est.0c03536.
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