As rapid urbanisation shapes more of the world with cement, glass and steel, modern cities are turning into heat sinks, but this is not an irreversible situation, says Professor Winston Chow. Chow is an Associate Professor of Urban Climate at the Singapore Management University and the lead researcher for ‘Cooling Singapore,’ a multi-institutional project launched in 2017 with funding from the Singapore government to build a computer model, or digital urban climate twin, of Singapore. This will allow policymakers to analyse the effectiveness of various heat mitigation measures before spending money on solutions that might not work.
“Every city will have a heat island,” says Chow, “It’s the inadvertent consequence of converting natural and rural landscapes into urban settlements by constructing with concrete and asphalt materials and having more fuel and energy use for power, heating, cooling and transport.
“The flaw in having large heat islands intensifies from a double whammy of ignorance of nature and its non-inclusion when planning cities. An absence of green spaces and inefficient use of energy and fuel in urban infrastructure results in heat islands. While sprawling cities lacking public transportation options are often associated with more private transportation use, which generally results in more fuel usage and higher heat island intensities.”
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Exhaustion and dehydration, power grid failures and crumbling infrastructure all result in heat stress, which requires building heat resilience. The most obvious way to fight the urban heat island effect is to reintroduce vegetation – expand green cover, plant street trees, install ‘green roofs,’ etc. Other options include introducing ‘cool roofs’ that feature bright coatings to reflect more sunlight and absorb less heat. While Zhuhai, a city of 2.4 million in the Guangdong-Hong Kong-Macao Greater Bay Area, is part of a pilot project in China promoting ‘sponge cities.’
A sponge city, according to Chinese guidelines, is one that has transformed hard surfaces, such as roads and pavements, into permeable surfaces that can absorb, seep, purify and store water and later release stored water for use. The adoption of porous bricks and porous concrete could lower pavement surface temperature by 12 and 20°C, respectively and the air temperature by up to 1°C.
Cities such as Singapore – and others that apply climate resilient development principles – are proactively reducing risks from heat islands and heatwaves. Their strategies for reducing heat impacts include more efficient physical infrastructure, such as district-level cooling that efficiently uses energy to mechanically cool large areas in cities; nature-based solutions, such as increasing the extent and density of green spaces in cities and on walls and roofs, and; integrated, inclusive planning of urban stakeholders to ensure that vulnerable urban residents are protected. For this final point, early warnings from meteorological agencies might be tied to enhanced health infrastructure to ensure elderly or medically vulnerable people have access to medical treatment or shelter, and there may be work stoppages for outdoor construction workers when heatwaves occur.
Sustainable cooling solutions
Using air conditioners and electric fans to stay cool accounts for nearly 20% of the total electricity used in buildings around the world and energy consumption for cooling has more than tripled since 1990, with significant implications for electricity grids, especially during peak demand periods and extreme heat events, according to the International Energy Agency (IEA). But encouragingly, a new study finds that switching to propane as a refrigerant could lessen the global temperature increase from space cooling, meaning that we could avoid a 0.09°C increase in global temperature by the end of the century, making a significant contribution toward keeping the global temperature rise below 1.5 °C.
Singapore has a few other innovations and radical designs that cities around the world could adopt to tackle extreme heat and avoid urban heat islands. Image: IEA
Air conditioning is a distinctive feature of cities experiencing extreme heat. This contributes to a sizeable proportion of carbon emissions and with the current energy crisis, it is also becoming unaffordable. So, how can we build more green buildings and consume less energy and stay cooler? How feasible is this model?
“While air conditioning has been, in Singapore’s founding Prime Minister’s words, one of the signal inventions in history’ and ‘a most important invention for Singapore,’ it does have its costs with exacerbating the heat island and global warming,” says Chow. “Two approaches that can work to reduce air conditioning use – especially where it is most needed in tropical cities – involve using it more efficiently.
“Firstly, district-level cooling is increasingly being utilised in Singapore in lieu of inefficient individual air conditioning condensers. As uptake of this option increases, the cost to operate these – as well as to the environment – will decrease. The second approach is to go back to applying historical tropical urban design and architectural principles in low-latitude cities dependent on air conditioning. There should be particular emphasis on using natural ventilation, artificial shading and vegetation cover to ensure that air conditioning use is significantly lowered.”
Urban planning and design innovations – The Singapore Model
Singapore has a few other innovations and radical designs that cities around the world could adopt to tackle extreme heat and avoid urban heat islands, adds Chow.
“Among the push towards more ‘green’ buildings and the implementation of the Singapore Green Plan 2030, is a move towards science-based policies in reducing urban heat risks,” he says. “Together with colleagues in several universities in Singapore, I’ve been leading research into the Cooling Singapore Initiative since 2017.
“Our most recent project involves developing an innovative Digital Urban Climate Twin that stakeholders can use to ascertain which heat reduction approaches give the ‘best’ outcome for different parts of Singapore’s urban landscape. This Twin is based on coupling several environmental models that are tested and parameterised with observed data to ensure that these are representative of Singapore’s urban climate context. It is hoped that it can contribute to ensuring the urban resilience of this city-state towards climate change-related heat risks.
“I think that a blueprint, such as the recent IPCC report for human settlements, for example, that enhances adaptation and resilience can be extensively followed. Singapore – and other cities such as Ahmedabad and Semarang in Asia – have track records in dealing with climate change risks from heat, flooding and sea level rises that will, unfortunately, be more frequent and intense in the years to come.
“There’s no secret ingredient to this. Among other things, inclusive planning, adequate finance and buy-in from stakeholders and adhering to science-based policies are essential for this blueprint to succeed. What’s certain though, is that if stakeholders in cities fail to plan, then they should plan to fail.”