Heatwave Solution: How 'White Roofs' And Rooftop Lawns Can Bring Relief From Urban Heat Island Effect

Scientists evaluated the effectiveness of two schemes mitigating heat island effect and improving human thermal comfort, as part of a study. These schemes are: "white roofs" and "green roofs".

"White roofs" are roofs with high albedo, and "green roofs" are roofs with a lawn. Albedo is an expression of the ability of surfaces to reflect sunlight, or heat from the Sun. | Representative Photo

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New Delhi: Human thermal comfort and living environment in urban residential areas can be improved by alleviating the urban heat island effect through regulation of urban landscape. However, the single environmental factor of temperature has been the focus of most precious studies. Also, the actual human feeling of thermal comfort, which is affected not only by temperature, but also by humidity, wind speed, and radiation, was not considered in the studies.

What Are Heat Islands?

Heat islands are urbanised areas which experience higher temperatures than outlying areas, according to the US Environmental Protection Agency (EPA). Structures such as buildings, roads, bridges, and other infrastructure absorb and re-emit the Sun's heat more than natural landscapes such as forests and water bodies. As a result, the urban areas where these structures are highly concentrated and greenery is limited become "islands" of higher temperatures relative to outlying areas. These pockets are known as "heat islands". 

The greatest temperature differences are experienced in humid regions and cities with larger and denser populations. According to several studies, the heat island effect will strengthen in the future because the structure, spatial extent, and the population density of urban areas change and grow.

What Are “White Roofs” And “Green Roofs”?

An international team of researchers recently conducted a study that integrated multiple environmental elements as an indicator of urban landscape regulation efficiency. The study, describing the findings, was recently published in the Building and Environment journal.

The scientists evaluated the effectiveness of two schemes mitigating heat island effect and improving human thermal comfort, as part of the study. These schemes are: "white roofs" and "green roofs".

"White roofs" are roofs with high albedo, and "green roofs" are roofs with a lawn. Albedo is an expression of the ability of surfaces to reflect sunlight, or heat from the Sun. Light-coloured surfaces are said to have high albedo because they return a large part of the Sun's rays back to the atmosphere, while dark surfaces are said to have low albedo because they absorb the rays from the Sun.

The scientists also studied the underlying mechanisms for these schemes.

According to the study, both the "white" and "green" roofs can effectively reduce the intensity of heat island effect by lowering wind speed and reducing radiation temperature. In this way, "white" and "green" roofs improve human thermal comfort.

The scientists revealed two measures that can effectively enhance the cooling effects of roofs. These measures are: roof sweeping and greening.

According to the study, roof sweeping and greening can increase albedo and irrigation, respectively. Therefore, the thermal comfort of humans in urban residential areas can be improved by undertaking these measures.

The study is important because the findings will benefit urban planning and the management of urban heat island effect.