Hong Kong is getting hotter, and not just during the sweltering summer months. The urban landscape with its closely packed high-rises and limited open space is trapping heat and restricting airflow, with the result that average ambient temperatures are edging up.
That creates more energy consumption, ostensibly to achieve cooling, but instead contributing more to the underlying problem. 'Flats have become warmer due to their compact nature,' said Yuguo Li, a professor at the University of Hong Kong's department of mechanical engineering. '[They are] good for trapping heat, but not for releasing it.'
Furthermore, the canyon effect created by skyscrapers, narrow streets and concrete surfaces, means that solar radiation is absorbed more readily, adding to the rise in temperature indoors and out. Most buildings are not designed to make the most of natural ventilation, so opening a window often does little to cool a room or apartment, even at night.
Recent infrared images show that some buildings in Central, particularly those with dark surfaces and glass facades register temperatures reaching 40 degrees Celsius. This is one of the most obvious manifestations of a phenomenon known as the 'urban heat island', which is now evident in many cities and is becoming a subject of increasing academic study.
In a 2006 research paper entitled Benefits and Potential Applications of Green Roof Systems in Hong Kong, Sam Hui of the University of Hong Kong's department of mechanical engineering addressed the topic. He pointed out how, in summer, the urban heat island increased the use of energy for cooling and accelerated the formation of urban smog. Dr Hui traced the problem mainly to the lack of vegetation and high absorption of solar radiation.
Several measures are recommended to mitigate these factors. Hong Kong needs more natural vegetation and open areas. And each of us can play a part by lobbying for change on a wider scale or simply starting our own garden on a roof or balcony.