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Green buildings cool down the city
According to a new update issued by the World Meteorological Organization (WMO) recently, global temperatures are likely to surge to record levels in the next five years, fuelled by heat-trapping greenhouse gases and a naturally occurring El Nino event. And the Hong Kong Observatory also warned that 2023 is likely to be one of the warmest years on record.
With the high population density and high-rise buildings in Hong Kong, people might easily suffer from heat-related illnesses or heat stroke when walking in the streets in summer. According to Professor Ng Yan Yung from the School of Architecture, the Chinese University of Hong Kong, the dense buildings form giant windshield walls, while the narrow streets block the ventilation corridors in the area, reduce the air circulation, affect the wind flow, and cause the heat to accumulate. Professor Ng's study found that the downtown areas such as Mong Kok, Causeway Bay, Kwun Tong and Tsuen Wan were the hottest areas, and the temperatures could be 3°C to 4°C higher than other areas.
Hot weather can make people sweaty, upset, and lose self control. Other places such as the United Kingdom, Mexico, South Africa, Greece, the United States and Finland have research figures showing the possible link between violent crime and rising temperature. High temperature also poses threats to human health, especially for long time exposure to extremely hot and humid environment. If water is not replenished in time, it may trigger diseases such as heat cramp, heat exhaustion, and heat stroke which is more likely to cause cell necrosis, organ failure, and even death. The mortality rate of heat stroke can exceed 10%, according to a local expert. In August 2020, Japan suffered from a series of extremely hot weather. In Tokyo alone, 187 people died of heat stroke in that single month, it was unprecedented.
In order to avoid the heat, many people choose to stay in cool places or turn air-conditioner on. However, as the demand for air-conditioning increases, it in turn fuels more greenhouse gas emissions. This vicious cycle will not only increase the heat in the region, but also intensify climate warming. It will continue to de-stablise the environment and ecology, and cause more heat waves and typhoons.
The United Nations Environment Programme published Beating the Heat: A Sustainable Cooling Handbook for Cities (the "Handbook") in 2021. It points out that cities are rapidly warming due to heat island effect, countries should adopt a whole-system approach to cool down the cities. The Handbook mentions urban cooling strategies, including reducing heat at an urban scale, reducing cooling needs in buildings, and meeting cooling needs in buildings efficiently. It also quotes successful examples to show how green buildings help cool down the city, it is worth learning.
For example, Toronto, Canada has implemented the world's largest lake-source cooling system and promoted the production of renewable energy. The municipal government of Guangzhou has adopted regional centralised cooling in the Zhujiang New Town, making the temperature in the area 2°C to 3 °C lower than when using a decentralised cooling system.
To combat climate change, Hong Kong has set a more vigorous interim decarbonisation targets to reduce carbon emissions by 50% as compared to the 2005 level before 2035. There was mentioning of "energy saving and green buildings" carbon reduction strategy. Green buildings have become the general trend of urban construction in recent years, many new buildings with BEAM Plus have appeared in Hong Kong one after another.
The Zero-Carbon Building under the Construction Industry Council implements the green concept with 100 plants and an innovative "layer grid" planting method to lay a large lawn. The bottom layer is equipped with a drainage system and water storage plant pots, which helps reduce irrigations, and a composite filter is installed in the middle layer to prevent siltation and allow luxuriant growth of grass. As a result, a sustainable, energy-saving and water-saving greening ecosystem is formed.
Green buildings cool down the city and mitigate climate change, while providing citizens with a comfortable environment. I hope that Hong Kong will have more green constructions to speed up the pace of sustainable cooling of the city, making Hong Kong a model of liveable city in the world.
Dr. Winnie Tang
Adjunct Professor, Department of Computer Science, Faculty of Engineering; Department of Geography, Faculty of Social Sciences; and Faculty of Architecture, The University of Hong Kong