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Tackling urban heat: Experts plan to cool a desert city by 4.5°C

Scientists from the University of New South Wales (UNSW) Sydney have developed a comprehensive plan to cool off one of the world’s hottest cities. The researchers outlined a strategy to lower the temperature of Riyadh, Saudi Arabia by as much as 4.5°C. 

Reducing extreme heat 

In collaboration with the Royal Commission of Riyadh, the experts present a multi-faceted approach combining “super cool” building materials, expanded green spaces, and energy-efficient retrofitting to tackle extreme urban heat.

The study was led by Professor Mattheos Santamouris, who is renowned for his work in developing strategies to reduce urban heat. The research is especially relevant as over 450 cities struggle with extreme heat, exacerbating energy consumption and posing severe health risks.

“The project demonstrates the tremendous impact advanced heat mitigation technologies and techniques can have to reduce urban overheating, decrease cooling needs, and improve lives,” said Professor Santamouris.

Urban heat island 

Riyadh, the capital of Saudi Arabia, is a prime example of an urban heat island. Encircled by desert, the city often experiences temperatures soaring above 50°C during summer months. 

Contributing factors include limited vegetation, heat-trapping conventional building materials like asphalt and concrete, and additional heat from vehicles and industrial activities. This scenario is further intensified by climate change and rapid urbanization.

The UNSW team conducted extensive simulations in Riyadh’s Al Masiaf precinct, analyzing the energy performance of 3,323 urban buildings under eight different heat mitigation scenarios. These scenarios combined various super cool materials, vegetation types, and energy retrofitting levels to identify the most effective strategies for cooling the city and reducing its energy requirements.

Pinpointing the optimal approach 

The simulations revealed that it’s possible to lower outdoor temperatures by nearly 4.5°C during summer months, while also conserving up to 16% in cooling energy. The optimal approach for Riyadh includes the implementation of super cool materials on building roofs and more than doubling the number of irrigated trees to enhance transpiration cooling.

The study warns against the indiscriminate application of urban cooling techniques without detailed scientific optimization. For instance, using non-irrigated greenery could inadvertently increase the city’s temperature.

“By implementing the right combination of advanced heat mitigation technologies and techniques, it is possible to decrease the ambient temperature at the precinct scale,” said Professor Santamouris. “For a sweltering city the size of Riyadh, significantly reducing cooling needs is also tremendous for sustainability.”

Far-reaching benefits 

Professor Santamouris noted that lowering the temperature of the city will help increase thermal comfort for people as well as reduce health issues from severe heat, decrease the concentration of pollutants, and improve human productivity.

Although not directly addressed in this study, previous research indicates that such cooling strategies can also reduce heat-related mortality.

Energy impact

The researchers examined the energy impact of retrofitting all 3,323 buildings in the precinct, in conjunction with the proposed urban-scale heat mitigation technologies. 

By optimally combining cooling technologies with retrofitting measures – like better windows, insulation, and cool roofs – the cooling demand could be slashed by up to 35 percent. 

“This represents a substantial reduction to the energy needs for Riyadh that would help further reduce costs associated with cooling for the city while improving the quality of life for the local population,” said Professor Santamouris.

Study implications 

The researchers now hope to work with the Royal Commission of Riyadh to begin implementing their heat mitigation plan, which will be the largest of its kind in the world.

“Once implemented at the city scale, these advanced heat mitigation technologies will deliver important health, sustainability and economic outcomes for the city for years to come,” said Professor Santamouris. 

The study is published in the journal Nature Cities

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