Failure to implement heat mitigation strategies posits grim reality for cities

by Helena Morgan
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World-first research reveals heat mitigation ‘green roofs’ can combat the increasingly lethal effects of intense urban heat. 

Indira Adilkhanova and Professor Geun Young Yun from Kyung Hee University in South Korea discovered rooftop greenery coverage is capable of cooling the city of Seoul by one degree Celsius during summer, in addition to decreasing the energy necessary for cooling by close to eight percent under maximum coverage. 

Heat mitigation technology specialist and UNSW Sydney Scientia Professor Mattheos Santamouris was also involved in the study. He said previous investigations exclusively assessed the impact of green roofs on singular buildings, yet this study evaluated the power of green roof coverages on a city scale. 

“Our findings demonstrate the tremendous potential of green roofs to decrease the peak temperature of a city and increase energy savings,” says Santamouris.

Rising thermal discomfort and major health issues

Seoul’s unstoppable urbanisation exacerbates the effects of overheating and places a major strain on energy demands – acting as a cautionary tale against failing to implement heat mitigation techniques. 

“As cities heat up, thermal discomfort and heat-related illness and death rise,” says Santamouris.

A hopeful answer is evident in green roofs, as they are a scalable and nature-based remedy to urban heating and can be installed on both new and retrofitted buildings.

Higher coverage equals hefty temperature decreases

To determine how green roofs decrease the temperature and cooling requirements of Seoul during the height of summer in August, the research team operated large-scale cooling climatic and building energy simulations under three greenery coverage scenarios. 

The team was particularly keen to focus on non-irrigated extensive green roofs – a form of lightweight green roof capable of large-scale implementation and carrying fewer maintenance costs. 

A compelling observation resulted – higher coverage green roof systems corresponded with hefty temperature and energy decreases. The modelling revealed that when 90 percent of the buildings were adorned with green roofs, Seoul’s air and surface temperature fell by 0.54 degrees Celsius and 2.17 degrees Celsius, respectively. Additionally, building energy use decreased by approximately 7.7 percent. 

Santamouris says the magic of green roofs in cooling surrounding air lies in the ability to incite evaporation via plant transpiration. 

The layer of soil and vegetation on green roofs provides insulation, reducing heat transfer into buildings and further lowering energy costs,” says Santamouris. 

Green roofs are socially valuable 

Although green roof coverage in Seoul is still in its infancy stages, widespread adoption is predicted at between 30 and 60 percent over the next few decades. Santamouris says while a 90 percent city-wide coverage sounds ambitious, and is not the most effective in regards to capital costs and regular maintenance, it is possible with thoughtful and considered measures.

“For cities and businesses that can afford it, green roofs are an important social contribution,” says Santamouris. 

While such findings are promising, he says further analysis is vital to understand the long-term cooling and energy-saving capacity of green roofs, as optimum effectiveness depends on humidity, precipitation, solar radiation, and temperature. 

The appeal of green roofs is not solely confined to climatic benefits, as they can also retain rainwater, enrich biodiversity and improve the aesthetic quality of the city. 

Urgency to implement heat mitigation techniques more pressing than ever 

Santamouris implores cities to implement urban heat mitigation strategies to dodge irreversible consequences such as night temperatures rising by up to five degrees Celsius by 2050.

Onerous cooling costs and heat-related illnesses and deaths will cripple populations – with vulnerable communities copping the brunt of these consequences. 

“If we do not implement heat mitigation techniques, the cost in the coming decades will be catastrophic, not just for the economy, but the quality of life for low-income populations who will suffer the most,” says Santamouris.

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