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Hong Kong struggling to breathe under weight of ‘maximum’ urban density, academic says

Hong Kong cannot cope with any more high-rise buildings, according to an academic, who says street-level airflow has become worryingly stagnant and unable to disperse heat and pollutants as urban density hits “maximum” level.

Though average wind speed levels measured at the Hong Kong Observatory’s remote Waglan Island weather station off the city’s southernmost island Po Toi have been stable over the last 50 years, average wind speed in the city has fallen as more tall buildings are built in higher density.

Wind measurements at the King’s Park urban weather station in Kowloon have dropped from 3.5 metres per second in 1965 to just 2 metres per second last year. The decrease in wind speed is in line with a 2 degrees Celsius rise in average air temperatures in the same period.

“I would say we are at maximum density, especially in built up areas … Future land reclamation may need to be more disciplined,” said Professor Li Yuguo, who heads the department of mechanical engineering at the University of Hong Kong.

Li said poor urban air ventilation could definitely be one of the factors behind days with very high air pollution readings.

Studies by Li’s team, which included wind tunnel and water channel modelling, have found that in the absence of wind, convective heat from individual buildings rises and forms a dome-shaped accumulation of warm air and pollutants above the city.

The phenomenon is called the “urban dome effect”.

“The worrying trend continues but there is no removal strategy for the urban dome,” said Li, adding that strong wind flows felt on some afternoons tend to be man-made “city winds” induced from the “urban heat island effect” rather than natural wind.

He urged secondary streets along the northern shore of Hong Kong Island to be kept “wide and short” to facilitate downslope wind flow from the hills.

More buildings could also provide basal openings of about 10 metres – such as the ground floor of HSBC headquarters in Central – to help improve low-level wind flow, he said.

“But of course, there are development challenges here,” he admitted. “The price to pay is not having a 7-Eleven on the ground floor of every building.”

Source URL (modified on Apr 2nd 2015, 9:04pm):

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