Civic Exchange, a well-known think tank in Hong Kong, argues that increasing density through constructing taller buildings might actually do more harm than good. Their reasoning, which is based on Hong Kong's geography, is contrary to what many urban planners and scholars advocate as “building up” is the urban planner’s dream.
The think tank explains how more densely developed and poorly ventilated neighborhoods with insufficient open space and blocked ventilation corridors, can absorb more heat which intensifies the urban heat island effect. In essence, with less ventilation and more impervious cover, less rainwater is absorbed into the ground and thus the temperature will feel warmer in the urban area.
The tall buildings that form the concrete jungle, will contain more of that heat which really intensifies air pollution as the wind is blocked by the buildings and thus the dirty air is trapped and inhaled by the public. Because the temperature in the urban area increases, it will inevitably be warmer and lead to a greater need for air conditioning. Hong Kong has many areas that have bad air pollution and high density (Mong Kok for example, with high levels of nitrogen dioxide and over 130,000 people per square kilometer).
With complete dependence on air conditioning, this results in more electricity consumption and emissions of hot air; both of which increase the urban temperature. Thus, this leads to a vicious cycle of pollution causing activities (driving and profligate AC use) which warms the temperature in the urban area where people live, and people need cool air to live comfortably which will release more pollution and then repeat the cycle again and again and again.
Higher density through taller buildings means more people living closer to public transit, amenities and social infrastructure. Thus, greater density can lead to more supply and help satisfy demand. This can help lower housing costs for the poor. But, it all depends on design because if those buildings are too close together (lots of examples of this in Hong Kong) then they can block ventilation corridors and thus there are greater air pollution exacerbation risks.
Civic Exchange calls for decreased plot ratios to improve ventilation. In essence, by decreasing a building's plot ratio, the developer is forced to construct smaller units to abide by the zoning laws. Smaller units might take the form of smaller buildings with less people and therefore lower density. My argument: decreasing plot ratios will inevitably make real estate more expensive by constraining supply and increasing demand; this has been argued by Ed Glaeser time and time again.
It is extremely tricky to decrease a building's plot ratio in a City that has such constrained land supply. Where I do agree with the think tank is their vehement support for more open and green space in Hong Kong. This would mean that municipal zoning laws would require more open space around a development. Having more open space for the public to enjoy is a great idea. It will also expand ventilation corridors thereby allowing wind to pass through the concrete jungle more naturally.
Maybe a quick lesson from their publication and this analysis is that buildings (commercial and residential) must be subject to providing recreational and open space in greater quantities. Depending on the jurisdiction, there should be mandated requirements for constructing open space when building a development. Indeed, this is challenging because there is only so much room. Higher plot ratios, as analyzed by the Civic Exchange will not help the air pollution problem in Hong Kong. It is those high density areas like Mong Kok that need to witness the construction of open space such as public parks and sports facilities to prevent further development from exacerbating the air pollution problem.
Key message: Would such urban planning and policy making mean that there is a trade-off between lower density (potentially keeping housing costs unaffordable) and better air quality?
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