Hong Kong is a unique city due to its complex geographical setting and its concentration of very high buildings. Researchers are taking advantage of this fact to study how cities are ventilated in order to provide guidelines for future city design.

Image: Wikimedia

The ventilation of cities is fundamental to the removal of heat and airborne pollutants. With more than half the world’s population now living in urban areas, ventilation is a growing health concern.

In Hong Kong, the average wind speed has declined every decade since 1968. “We think this is due mainly to dense urban development, especially the inclusion of podiums,” says Professor Janet Nichol of The Hong Kong Polytechnic University. “The podium around most residential developments extends almost to the plot boundary, leaving hardly any open space at ground level for cooler fresh air to penetrate into the city.” Podiums are large projecting structures at the base of a tower block that commonly contain shopping malls or car parks.

As a result, “The air in the city’s centre is stagnant as it cannot be flushed out by penetrating winds,” says Professor Nichol. “This means that local pollutants from traffic accumulate near where they are generated: within streets and in urban canyons surrounded by tall buildings.”

In collaboration with the University of Hong Kong, Nichol and her colleagues hope to better understand the city’s ventilation mechanisms in different wind conditions. They also hope to determine the roles of building height, vegetation, sea breezes and other urban parameters on ventilation, and to compare ventilation conditions in Hong Kong with those in China’s city of Shenzhen to provide guidelines for future city design.

“Hong Kong provides a unique world laboratory for studying city ventilation due to its concentration of very high buildings and its complex geographical setting,” says Professor Nichol. The ultimate goal is to guide urban ventilation planning in rapidly developing cities in Asia and around the world.

So far, the team has spent several months collecting data on urban heat island patterns and distributions in Hong Kong’s largest and most extensively built-up area, the Kowloon Peninsula. The urban heat island effect occurs in large metropolitan areas due to high levels of human activity converting them into “islands of heat”.

“In August 2013, we measured the wind directions and wind strength at ground level on hot summer nights across the coastline in Hung Hom district,” says Professor Nichol. “We also flew over Kowloon on a hot day in August taking thermal images of Kowloon’s urban heat island from a helicopter.”

In 2014, the researchers plan to repeat the helicopter thermal survey during a night-time flight. “At the same time, we will collect ground data on wind at the urban edges to identify the major ventilation pathways across Kowloon and those areas where air is stagnant,” she says. “We will also build 3D models of temperature and ventilation corridors across the urban area.”

For further information contact:

Professor Janet Nichol
Department of Land Surveying and Geo-Informatics
The Hong Kong Polytechnic University
Email: lsjanet@polyu.edu.hk