Rising urban temperatures also leads to increased energy consumption

In the rush to build, Hong Kong must keep cool

Florence Lee says Hong Kong must reconsider its push to pack ever more flats into already dense urban areas, as the costs to health and the environment may outweigh the benefits


The government is planning to increase the plot ratio by 20 per cent or more in some densely populated areas such as Kai Tak and Tun Mun East to boost housing supply.

Earlier this year, Secretary for Development Paul Chan Mo-po said raising the plot ratio for several sites at Kai Tak would provide an additional 6,850 flats and raise the population capacity by 20,000 to more than 110,000. He also mentioned maximising the development density of the Tuen Mun East land plot, allowing for 8,000 new homes - or eight times the original plan.

These numbers and statistics seem positive. However, as with any large urban planning project, they also hide some complex realities and negative consequences. Such initiatives need more scrutiny and environmental assessment.

As a small city with an already high population density, any expansion plan will need to be thoroughly evaluated. What will the effect be on quality of life if building density and height increases substantially? Will there be adverse environmental and climatic effects? More importantly, what are the implications of a higher, denser Hong Kong for future generations' health and livelihoods?

Arguably, the biggest environmental impact of increasing plot ratios will be a bigger temperature difference between urban and rural areas - the "urban heat island" effect. It is not surprising to learn that Hong Kong's high-rise buildings already cause the city centre to heat up dramatically. High-resolution thermal satellite images from 2007 showed that our urban areas are up to 7 degrees Celsius warmer than open land - and it is getting worse. Scientists fear the difference could be as much as 10 degrees by 2050.

This temperature variation has many adverse health and environmental effects. First, retained heat worsens the air quality of the surrounding environment. In areas with lower building densities, heat and exhaust fumes are released into the surrounding air and rise up above the cooler, heavier air on the ground. As air moves upwards, pollutants and dust are lifted up.

With more tightly packed buildings and urban heat, the ability of pollutants to rise and disperse was reduced, according to a report by non-governmental organisation Green Power. Many air-cooling facilities are installed on rooftops, causing a temperature inversion with higher temperatures at the top. Pollutants released from below cannot disperse upwards and air pollution is intensified.

Second, higher temperatures and sunshine combine with air pollutants to produce ozone and secondary pollutants. This creates city smog, which is trapped between densely spaced buildings.

Third, rising urban temperatures also leads to increased energy consumption. It is estimated that 3 per cent to 8 per cent of Hong Kong's electricity consumption is used to combat the urban heat island effect - with air conditioning, for instance. Further, it is estimated that a 3-degree rise in temperature can increase electricity consumption by 30 per cent for residential consumers and 10 per cent for commercial consumers. This higher energy use will impose an economic cost and affect the environment. Lastly, higher plot ratios and more urban heating will harm people's health. In the hot summer months, high temperatures reduce workers' efficiency and increase the chance of heatstroke for those working outdoors. High temperatures can severely affect the elderly and those suffering from chronic illness. Higher temperatures can also facilitate the spread of infectious diseases. Studies have shown that for every 1-degree rise, the risks of dengue fever and malaria increase by 1.2 per cent and 6.7 per cent respectively.

By building on less densely populated areas such as Ta Kwu Ling and Kai Tak, Hong Kong would increase the size of its "heat island". Green Power estimates that the urban heat island effect results in a 3-degree rise on average for every kilometre towards the urban centre. Thus, for every kilometre the city grows outwards, the temperature in the city will increase by about 3 degrees.

If we consider the Wan Chai and Central reclamation, plus the proposed plot ratio increases, this can only mean significantly higher temperatures in the heart of the city. Old districts will heat up even more. This, in turn, will affect the health, safety and livelihoods of people. All this can only have a detrimental effect on Hong Kong's reputation as a clean and attractive world city. If the city wants to expand and keep its competitive edge, it has to do so sustainably and healthily.

From the perspective of both the urban developer and informed citizen, there is a need to reconsider whether high-density residential areas are conducive to quality living. Of course, to retain Hong Kong's competitiveness, it will be necessary to constantly improve the urban environment. But, rather than pushing a narrow, singular vision to increase the number of apartments by maximising land density, the chief executive needs to commit to a broader and more holistic picture of long-term development that enhances, rather than degrades, the quality of living.

This article appeared in the South China Morning Post print edition as: Hot in the city