A Scientific Approach to Urban Cooling: Mitigating the Urban Heat Island Effect

If you look at a thermal image of an urban area and then compare that to a map of vegetation, you'll find that where there's greenery, the temperature is lower. That's because things like asphalt, concrete and shingled roofs absorb more heat from the sun than trees. This is the urban heat island effect, and it accounts for the higher temperatures in built-up areas, often by several degrees compared with their surroundings. It's becoming a huge risk to human health as growing urban populations exacerbate the heating effects of climate change. Heat waves kill more people than any other extreme weather event, more than tornadoes, hurricanes and even floods. That's why urban heat island mitigation strategies are being studied in Singapore by a group of researchers. The government-backed project called Cooling Singapore is now in the process of combining everything they've learned to create a digital tool that can help urban areas all over the world, starting with Singapore.

I. Singapore's Heat Challenge and Novel Cooling Solutions

In Singapore, close to the equator, temperatures regularly rise above 32 degrees Celsius or 90 degrees Fahrenheit. The structures only make it worse. And that is also the case for Singapore, which is basically a concrete jungle, more urbanized, more developed. Even in Singapore, what you have is a situation whereby there's a temperature difference of 7 degrees Celsius between the more urbanized and the more rural areas. The government has taken drastic steps to keep temperatures down.

The World's Largest Underground District Cooling System

This is Gardens by the Bay, an award-winning park. And inside this greenhouse it's a pleasant 24 degrees. That's because the dome, along with two dozen nearby towers full of thousands of people, is chilled by what's probably the **world's largest underground district cooling system**. It uses a large central plant that cools water and then pipes it into banks, residential towers, an exhibition center, shopping malls and the iconic Marina Bay Sands hotel and casino complex. One of the biggest perks of using this system for the buildings is that they can save **40% in terms of electricity usage** compared to traditional air conditioners. And with Singapore relying on natural gas for most of its power, this new system means emissions savings equivalent to removing 10,000 cars from the roads. That has big implications for the rest of the world.

II. Breaking the Vicious Cooling Cycle

If things stay as they are, more than a third of the world's electricity could end up being used to cool buildings and vehicles by 2050. As the world gets hotter, gets warmer, there is a greater need for air conditioning and as well as refrigerators, for instance. The more people are buying these household appliances, the more energy usage they use and they release heat more, and that then exacerbates climate change. It's a **vicious circle**. And so since 2017, researchers at Cooling Singapore have been identifying design solutions that reduce our need for so much cool air in the first place.

III. Vegetation: The Primary Cooling Technology

One thing many urban areas have in common, and that's the importance of **vegetation**. That's a very important measure to mitigate the urban heat because of the shading effect, of course, and deep psychological effects of the vegetation. And also because of the possible **evaporative cooling effect** of the vegetation. Vegetation can be, of course, on the ground floor in form of trees and shrubs. And you can walk under them. This is the so-called **canopy layer** that the vegetation forms above us. But vegetation can also go up the facades of buildings and it can go to the roof of the buildings.

Singapore’s Green Design Initiatives

Luckily, Singapore has been striving for the **Garden City** feel for quite some time. It was a vision initially introduced by then Prime Minister Lee Kuan Yew in 1967 to make life more pleasant for people. And today, Singapore is one of the world's greenest areas in terms of urban vegetation.

• Kampung Admiralty, a community center that contains health facilities and social spaces, now provides more green space than the plot of land it was originally built on. It's topped by a roofscape of staggered terraces covered in local plants, which functions as a community park, and a village green in the center that contains farm plots for residents to tend to.
• Parkroyal on Pickering was designed as a hotel in a garden that doubled the green-growing potential of its site. There's now 15,000 meters of sky gardens, reflecting pools, waterfalls, planter terraces and green walls.

The government has big plans as well. Singapore actually has a plan to plant **1 million trees** and add more green spaces over the next 10 years. It is actually a mix of one thing to reduce the urban heat island effect. But on the other hand, it's also to to get the people to be more connected to nature. But it's not enough. The region has still been warming **twice as quickly as the world average** over the past six decades. That's why Cooling Singapore has developed a catalog of other potential heat-mitigation measures.

IV. A Catalog of Heat Mitigation Strategies

When you try to mitigate the urban heat island effect in an area or in any building, in a village as well, the first place to start is by **shading the windows**.

• You have to keep areas clear so that the **wind can move** through it.
• **Water of a certain depth** can act as a very good thermal buffer.
• If you have to construct heavy buildings, such as high rises, at least you can make the surface, the facade less heavy.
• And you can protect it from direct sun penetration. We have to make sure that **no combustion engines** will be in the area in the medium- to long-term range.
• Ideally, the electricity production is outside of the area. And you bring just the clean electricity into the area.
• You can at least minimize the use of energy in the area.
• And you can start to slowly convert the roofs, the facades of the buildings, into **production areas for renewable energy**. In Singapore, unfortunately, this is a limited option. But in the long run, it could produce up to 20%, 25% of the energy, of the electricity needed in Singapore. If all the roofs and the areas in the buildings, on the buildings, on the facades would be used to do that.

V. Modeling the Future: The Digital Urban Climate Twin (DUCT)

With so many different ideas, Cooling Singapore is also designing a **virtual model** of the area to test them out. It's called a **Digital Urban Climate Twin, or DUCT**, that will calculate how each element of the design will impact the urban heat island effect.

That means we model not only the geometry of the buildings digitally, but also we model the transportation, the insulation, the temperature, the radiation coming from the sun, the weather, the local weather, the local climate, the even very, very microclimate of the area, the water, the movement of people in the area. We can invent scenarios. We can design scenarios, test them before we actually build them. And if they test very well and we are sure that they will function, then we can start to build them and put them into reality.

Global Implications of the DUCT

Singapore will be using this new tool to figure out which actions it should take next. And the model can be applied to any urban area, whether it needs to keep heat out or keep heat in, which will ultimately save energy, slow climate change and improve our quality of life. This is something that Singapore will be able to export, maybe even together with its urban development systems that it already has. Singapore is one of the very few urban areas in the world that really combined this scientific approach with a very well-established urban redesign and urban design approach. Through its agencies and the combination of its agencies, it has achieved a lot in the past. If it keeps following the scientific path and the combination with the other knowledge in the area already, we think that it will be a very comfortable and very livable area in the future, even more than today.