Hot Tech to Keep Singapore Cool

The Cooling Singapore project has been working to tackle urban heat, or the urban heat island effect, since it started in 2017. It aims to improve residents’ outdoor thermal comfort and well-being, and also to improve Singapore’s liveability and sustainability.


We speak to Cooling Singapore researchers from the Singapore-ETH Centre and the Singapore- MIT Alliance for Research and Technology to find out how the project helps helps keep Singapore, cool. Dr Heiko Aydt, computational scientist and lead investigator of the Digital Urban Climate Twin R&D pillar, and Dr Juan Angel Acero, climatologist and lead investigator of the Climate and Vegetation pillar, answers our questions.


Cooling SG once announced creating a “digital twin” of Singapore as a model that allows researchers and policymakers to find out factors that affect outdoor temperatures. Could you explain how this works and the progress so far?


Heiko Aydt (HA): If Singapore could manage its urban climate through climate-responsive design, it would help to counter some of the detrimental effects of climate change and urban development on the urban climate, and more importantly, on the residents’ thermal comfort and health.


In order to do so, two capabilities are required. First, we need the ability to evaluate how changes in the urban landscape; for example, redevelopment of an existing neighbourhood which would affect the local climatic conditions. This will help planners to better understand the implications – the pros and cons – of alternative planning scenarios.


Second, we need to know how public health, the economy and ecosystem will be affected by changing climatic conditions. Specifically, we want to better understand the risks of rising temperature and the potential benefits of heat mitigation.


The ‘Digital Urban Climate Twin’ addresses the first need. It allows planners to ask the ‘what-if’ questions and provides the relevant information required for better-informed urban planning and design to enhance Singapore’s climate resilience.


What have you uncovered from the data things that impact temperature in Singapore?


Juan Angel (JA): Through modelling studies based on data shared by the agencies, our initial findings in an earlier phase of Cooling Singapore is that the major contributor to the urban heat is the building mass in Singapore. Buildings alone, without taking into account any indoor activity or air-conditioning (i.e. passive buildings), have a spatial mean impact of 1.8ºC in air temperature on the urban area. Depending on the urban typology and region in Singapore, the impact on air temperature varies, reaching a maximum increase of 3.7ºC in the early morning (averaged values in April). Air-conditioners in buildings are also contributors, although significantly lower than building mass. In the daytime, the impact of air-conditioning on 25 percent of the urban area is more than 0.6ºC in air temperature, reaching up to 1.4ºC in certain areas.


Current data shows that motor vehicles contribute up to 0.9ºC near the source of heat emissions (roads) in the morning period. However, the impact is lower than air-conditioning – only 4.6 percent of the urban areas experience more than 0.4ºC increase in air temperature due to vehicular traffic. Industrial processes, although major contributors of anthropogenic heat in Singapore, have not been fully analysed, and is being studied further. Its impact will be evaluated when the characteristics of the emission sources are available.


HA: In the earlier phase, we also identified a number of knowledge and technology gaps, specifically, the need for climate-sensitive urban design and management capabilities. The development of the Digital Urban Climate Twin is a direct consequence of these findings.


Could you share how you would use such data and modelling to help optimise land use to affect urban heat and improve outdoor thermal comfort? What elements of smart urban design could be incorporated to mitigate heat?


JA: Mitigation of urban heat should be done by reducing heat accumulation on urban surfaces and promoting the removal of overheated air inside the urban canopy layer; for example, increasing ventilation. In this sense, adjusting the urban geometry of the city, like orientation and width of streets, and specific location of urban elements with respect to the prevailing regional air flow, can mitigate the heat.


Also, new materials and coatings that minimise heat accumulation in urban surfaces, such as roofs, facades, and pavements, are currently available in the market. Finally, the use of vegetation, although already a well-known strategy to beat the urban heat, can be further optimised by understanding how location, combination and type can impact the effectiveness of urban heat mitigation.


The most important thing to consider is that there is no one solution for every urban area and that the same mitigation strategies may not have the same impact in different urban settings. Thus, interventions to mitigate urban heat must be tailored to the specific context where they are applied.


Two types of urban heat sources can be identified – the radiative heat from the sun that is trapped in the urban fabric and anthropogenic heat emitted during human activities in the city such as road traffic. We can avoid the accumulation of heat by, for example, using suitable materials, but also facilitate the dispersion and removal of urban heat generated in the city.


HA: The Digital Urban Climate Twin would provide a better understanding of the urban environment and its local climatic conditions, allowing planners to take an iterative approach in planning. This means that we will be able to iterate over multiple scenarios and their variations in order to better understand the pros and cons. For instance, planners may explore if small plots of urban parks or having larger continuous stretches of greenery would be more beneficial in improving the urban climate.


With air-conditioning becoming a norm for Singaporeans to fight the tropical heat, what ways do you think we can avoid this in terms of a bottom-up versus a top-down approach?


JA: These two approaches are adequate and are in fact necessary. People need to realise that increasing the set temperature of air-conditioners will not necessarily reduce their indoor thermal comfort, but will reduce the anthropogenic heat emitted outdoors. This will benefit the outdoor air temperature and also reduce the building’s energy consumption.


Of course, urban design strategies and building morphology and characteristics, such as the orientation of buildings and adequate thermal isolation, should be considered.


Also, buildings could be designed to enhance natural ventilation to improve indoor thermal comfort (in certain conditions) and avoid the extensive use of air-conditioners.


What kind of technologies and capabilities do you think are required to overcome this?


JA: To reduce urban heat, certain emerging technologies could be implemented at a larger scale, or even island wide. For instance, the replacement of all motorised vehicles with electric vehicles could reduce the impact of motorised vehicles on air temperature by about 80 percent. Also, district cooling could be a way of centralising the emission of heat in areas and avoiding the impact of the multitude individual split units.


HA: Considering climate resilience as one of the many parameters of urban planning requires that decision makers understand the risks of rising temperatures, the effectiveness of urban heat mitigation strategies and the implications of their actions. The Digital Urban Climate Twin is being developed to equip decision makers with the necessary technological capability to address these.


The Digital Urban Climate Twin is not a stand-alone technology. Instead, it is a federation of distributed, loosely coupled computational models that represent the different facets of a city, including environmental, land surface, industrial, traffic, building energy, among others. Each of these models requires careful design, development, and validation by the respective domain experts.


Operationalising this digital twin requires cloud computing and high-performance computing resources across multiple organisational domains. Due to its federated nature, there is likely going to be stakeholders across multiple organisations and administrative domains – each hosting, maintaining and operating their respective components, all of which are part of Singapore’s Digital Urban Climate Twin.


Do you also believe there’s a role for enterprises and start-ups to play in this as well?


HA: Small, hungry and agile start-ups have the ability to disrupt and change the way we do things.


A good example is SpaceX which has radically changed the way the space industry works. The idea of reusable rockets has been laughed at - until SpaceX showed that it is not only possible, but also allows bringing payload into space at a lower cost with potentially increased reliability. ‘Flight proven’ rockets may turn out to be more reliable than their brand-new throwaway relatives.


Similarly, in the context of the Digital Urban Climate Twin, our ambition is to challenge the way things have been done through innovation. Furthermore, the idea of the Digital Urban Climate Twin is not limited to Singapore. Many other cities in the region and around the globe would be able to benefit from such a technology.


How is Cooling Singapore supporting the nation’s efforts to mitigate heat?


JA: We have analysed strategies such as reducing the albedo of urban   materials, implementation of electric vehicles in Singapore and expanding district cooling systems in the city. However, the continuous expansion of the urban footprint might not only change the local climate in the specific land parcels, but might also affect the air temperature of the surrounding areas. Therefore, the ongoing conversations with the relevant agencies are important in ensuring that our research is not only relevant to the current situation, but also engages with future developments.


HA: I agree. The Cooling Singapore team is directing its research efforts to help mitigate the urban heat problem faced by Singapore, in close consultation with the Ministry of Sustainability and the Environment, the Urban Redevelopment Authority and other agencies. In addition, heat mitigation involves climate-sensitive urban design, the reduction of anthropogenic heat (which also reduces carbon emissions) and increasing vegetation, among other strategies. These are very much aligned with the Singapore Green Plan 2030. The end goal is the same: to make Singapore more sustainable, liveable and climate-resilient.


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