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【Policy Address Series】If I were the Chief Executive, I would Enhance the Urban Greening

Hong Kong has been facilitating various urban greening projects over the years, for example, greening the rooftops of government buildings and streets, but the results were not satisfactory. According to the "LCQ22: Green roof projects” on 3 June 2015,[1]the government only focused on greening government buildings and primary and secondary school premises, providing no financial assistance to property owners of private buildings. Strengthening urban greening policies gives Hong Kong one more tool, in addition to energy and carbon reduction, to improve air pollution and other issues.

Urban Greening Less Than Ideal?

Green roofs are one of the most common and popular urban greening project. International cities all over the world have included the concept of green roofs in urban or architectural planning. As mentioned earlier in the article, Hong Kong's green roof planning lags behind the world and needs to be improved. Take Japan for example. In 2001, Tokyo stipulated that all new buildings require green roofs. For private buildings with a construction area of more than 1,000 square meters and public facilities of 250 square meters, including new construction, renovation or all expansions require more than 20% of the roof to be greened. In 2005, this extended to all of Japan.[2]In the West, such as Toronto, San Francisco and Germany, these places have already included green roofs as part of urban planning practices.[3]

In contrast, Hong Kong, as an international metropolis, has not fully implemented the concept of green roofs. Although the government has started to green roofs, the momentum was not enough to encourage other facilities and buildings to adopt the concept. According to the 2020 report from the Hong Kong Green Building Council,[4]about 1,600 private and public projects in Hong Kong have been registered with BEAM Plus certification—which requires buildings with more than 1,000 square meters to have at least 20% green coverage. For those 1,600 private and public projects[5], this represents 40% of the new buildings built since 2010, but it only accounts for about 3.2% of the 50,000 existing buildings in Hong Kong.

Greening to Cool Hong Kong?

Hong Kong is placed fourth in population density.[6]With a small area and a large population, the city is over concentrated with urban development, making buildings excessively dense. The formation of dense buildings and walled buildings makes it difficult for heat to be released back to space. Also, the development of urban areas generates man-made pollutants and heat, which easily lead to urban heat island. In fact, it is easy to find out that the average temperature in Hong Kong has increased every year, from 21.5°C in 1885 to 24.5°C in 2020. The annual mean temperature rose by an average of 0.13°C per decade from 1885 to 2020, but increased to 0.24°C per decade during 1991-2020 in the latter half of the 20th century.[7]In addition, Hong Kong's roads are among the most heavily used in the world.[8]Heavy vehicle emissions have also intensified heat island effect.

As such, it is necessary for Hong Kong to fully integrate green roofs. According to the U.S. Environmental Protection Agency, green roof temperatures can be 4°C cooler than typical roofs.[9]Plants can regulate building temperature through evapotranspiration. The most important point is that green roofs can reduce air conditioning demand and greenhouse gas emissions (GHG). Therefore, green roofs can definitely cool and solve Hong Kong’s heat island problem.

What About Vertical Greening?

As mentioned above, green roofs are one of the options for urban greening, which brings many benefits to the society. In addition to greening the roof, vertical greening is also a good option. The environmental benefits brought by vertical greening are very significant, especially for heat dissipation. According to the "Study of Vertical Greening Application” done by Drainage Services Department[10]the temperature of exterior walls can decrease by 7°C in the summer with vegetation cover. The green wall also bring significant aesthetic and ecological benefits to the surroundings and nearby residents.In another example, CUHK trialled green walls in Yau Lai Estate and found that on hotter days, the difference between the green wall and the original concrete wall can be as high as 16°C, and the indoor temperature difference is as high as 3.5°C[11]. Utilizing the exterior walls of buildings can make more use of the area of the building and not be limited by the roof of the building.

Greening Hong Kong for a Green Future

The concept of a green city is not well implemented in Hong Kong, lacking in long-term planning. To tackle climate change and achieve carbon neutrality, Hong Kong needs to catch up with international standards on urban greening practices. Taking Singapore’s PARKROYAL COLLECTION Pickering as an example, the design of the hotel takes references to terraces, planting more than 20 plant species that can provide shading and adopting a large number of environmental protection concepts such as green walls, artificial water features, rainwater irrigation, and more. All of these equipment are also powered with solar energy[12]. Being able to mix green elements into the design while taking into account of the impact on the urban environment, Singapore's approach is worthy of Hong Kong's reference. I believe that the city is capable of implementing green city policies to turn itself into the leading green and low-carbon metropolis, meeting carbon targets and even becoming an urban greening leader for other places.

Interested Topic:
City Forestry, Forestry City
Climate Change
Eco City

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