Feeling the heat

The urban heat island effect is something most of us have experienced first-hand, with high concentrations of heat-absorbing buildings, concrete and asphalt making cities up to 7% hotter than surrounding countryside.

Urban heat islands (UHIs) are a real dilemma – as the world warms up, demand for cooling and refrigeration increases, and in turn more heat is expelled onto city streets, further affecting outdoor thermal comfort (OTC).

One impact is public health, with higher air pollution levels leading to more heat-related illnesses. But there are solutions, with researchers and built environment scientists across the globe working hard to find new ways to mitigate UHI effects.

Cooling down our cities

How we design our cities has a massive impact on global decarbonisation efforts. Although the combined physical footprint of the world’s cities today amounts to only around 2% of total land mass, cities account for two-thirds of global energy consumption and 70% of greenhouse gas emissions. On top of that, while roughly half the world’s population lives in cities today, predictions are that this will rise to 68% by 2050.

The number of cities exposed to extreme temperatures is expected to triple over the next decades, according to global climate leadership group C40 Cities, with almost 1,000 cities across the globe set to experience average temperature highs of 35˚C. Regions at greatest risk from extreme heat include South East Asia and countries in the Eastern and Southern Mediterranean and the Persian Gulf.

It’s clear that design strategies to reduce heat build-up in our cities and reduce reliance on artificial cooling are urgent.

Looking to Singapore

One well known study into mitigating UHIs is Cooling Singapore. Conducted from 2017–18, the first phase developed a catalogue of integrated heat mitigation measures for cities. These span from urban planning aspects, such as introducing green and blue infrastructure, to rethinking building massing as well as reducing energy expended on transport and cooling. At the level of individual buildings, the study has investigated shading methods and looked closely at materials and surfaces alongside presenting a set of metrics and tools for measuring UHI and OTC.

Currently in development, Cooling Singapore 2.0 introduces a digital urban climate twin to the equation and is looking at climate-responsive design guidelines.

At a glance

The general principles of cool cities extend beyond Singapore’s tropical climate. Key measures are:

• Introducing more vegetation to cities including green roofs, walls and facades, parks and open spaces 
• Urban planning measures to reduce heat build-up, such as variations between building heights and ‘breezeways'
• Introducing cooling blue infrastructure like ponds, lakes, wetlands and fountains to act as ‘cool sinks’
• Employing cool materials and surfaces, including cool facades
• Introducing shade via building orientation and shading structures
• Reducing private vehicles, improving public transport and transitioning to electric power to reduce emissions
• Minimising the energy consumption of buildings through design and by measures such as district cooling.

The role of building facades

The basic science of cool facades has been around for centuries – with roofs and walls of buildings in hot countries traditionally painted white to reflect rather than absorb heat.

Today, whether retrofit or new build, cool facades mean reducing building surface temperatures to lower surrounding air temperature and minimise UHI effect in our cities. It’s a win-win because naturally cooler buildings mean less energy use. 

The good news for design is that 21st century innovation means that cool facades no longer have to be white or even pale. To find out more, read our interview with Axalta Specifications Manager Merce Berengueras here.

To explore Cooling Singapore click here