Newsletter 270 --- News

As the poet Christina Rossetti wrote two centuries ago, the wind is invisible. Its presence is often alluded to by the music of a chime, the death of a flame or the dance of a canopy in Mongkok. And its absence, though not always immediately noticeable, is implied by a pervading sultriness, insidious conditions and general malaise.

Canopies in Mongkok have not been dancing enough, according to a study led by the Department of Architecture of the Chinese University for the setting up of an assessment system for air movement to be used in planning developments, just as traffic and infrastructure studies are already in place. The study was commissioned by Planning Department of the Hong Kong government in October 2003 as a pledge to tackle Hong Kong's wind problem upfront due to lessons learnt from SARS and now made all the more pertinent by the looming threat of avian influenza. In fact it was the then Chief Secretary, Donald Tsang's Team Clean, set up after the SARS outbreak, which suggested the need to examine 'the practicality of stipulating air ventilation assessment as one of the considerations ... for all major development or redevelopment proposals and in future planning.'

The reasons for Mongkok's malaise have been found to include narrow streets, the presence of tall, densely packed buildings, and the lack of breathing spaces for people and structures alike. Poor ventilation has over time led to temperature rises, concentration of pollutants, making urban areas like Mongkok a hotbed of disease and discontent.

A city's ventilation is affected by wind speed and direction, building height and layout of buildings. Chief investigator of the study, Prof. Edward Ng of the Department of Architecture, said it was unprecedented for densely populated, sub-tropical cities. Mongkok and Tseung Kwan O were quoted as typical examples of a metro area and a new town for discussion and eminent international scholars were asked to provide a qualitative assessment of the territory's urban environment. Ng stressed that the study was more about seeking good design for Hong Kong's wind environment than trying to prohibit anything.

Making reference to state-of-the-art wind science, the study found the main culprits of stagnant city air to be the prevalence of tight and narrow streets not aligned with prevailing winds and flanked by very tall, bulky buildings. The concentration of such buildings act as a windbreak and their uniformity in height results in wind skimming over the top. Airpaths are further restricted by the absence of open spaces, minimal gaps between buildings, excessive podium structures, and obstruction on streets. There is also a general lack of greenery.

Guidelines proposed include creating roads, open spaces and corridors of low-rises so that wind can penetrate the urban fabric. Major roads should be aligned parallel to the prevailing wind direction, and, where possible, open spaces should be linked and aligned to form breezeways. And any wind problem along the waterfront should be dealt with locally so that sea breeze is not obstructed.

Building heights should be stepped in rows to create better wind at higher levels while podia should be avoided. Hong Kong's ubiquitous podium structures are not desirable from the viewpoint of street-level ventilation as they not only block most of the wind to pedestrians but also minimize the 'air volume' near the pedestrian level.

Proper orientation and layout of the buildings with adequate gaps between buildings are necessary. Block arrangement should be staggered such that those behind are able to receive the wind penetrating through the gaps between blocks in the front row. Block heights should be varied with decreasing heights towards the source of the prevailing wind.

The study also recommended the use of cool materials, i.e. materials characterized by high solar reflectivity or high emissivity for pavements, streets and building facades, and the planting of trees on urban streets to provide shade and cooling.

In December 2005, the Planning Department issued draft design guidelines based on the study's recommendations. While it is not mandatory for developers to follow these guidelines, the government has requested quasi-official organizations such as the Urban Renewal Authority, the Housing Authority, and the two railway companies to include assessments of air movement when planning developments.

The first candidate to apply the assessment is the site of the former Kai Tak Airport and Ng has been appointed adviser to the master planners of City Planning ─ Maunsell/Planning Department for the site. Other major government sites like the West Kowloon Cultural District and the Tamar Site are in the pipeline. The government will issue a joint bureau-level technical circular early next year requiring all government projects to undergo the assessment. This is expected to affect hundreds of projects in the coming few years.

Buildings will continue to heap up on Hong Kong's horizon as the city continues in its flight path of high-income urbanization. But with the new guidelines in place, hopefully, as its inhabitants sit in their fluorescent-lit cubicles searching for lost words and worlds on Google, they will know that the wind has not forgotten them.