Newsletter No. 270

'Who has seen the wind? Neither I nor you.' CUHK LeadsQuestto Save Suffocating Urbanites 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. Prof. Edward Ng Pioneering Study on Hong Kong's Stagnant Air 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 infrastrcture 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 c o n s i d e r a t i o n s . . . f or a ll ma j o r d e v e l o pme nt or r e d e v e l o pme nt 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 b r ea t h i ng spaces for peop le and structures alike. Poor ventilation has over t i me led to t emp e r a t u re rises, concentration of pollutants, making urban areas like Mongkok a hotbed of disease and discontent. Labyrinthine Urban Design 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 p r ov i de a qualitative assessment of the territory's urban environment. Ng stressed that the study was more about seeking good d e s i gn f or H o ng Ko n g 's w i n d 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 w i th 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. Wind-friendly Recommendations 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 l i n k ed and a l i g n ed to f o rm breezeways. And any wind problem along the waterfront should be dealt with l oca l ly 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 ub i qu i t ous p o d i um 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 b u i l d i n gs are necessary. B l o ck arrangement should be staggered such that those behind are able to receive the w i nd 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 ma t e r i a l s, 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. Guidelines Adopted by Government In December 2005, the Planning De p a r t me nt issued d r a ft design gu i de l i nes based on the study's recommendations. Wh i le it is not mandatory for developers to follow these g u i d e l i n e s, the g o v e r nme nt 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 P l a n n i ng — Ma u n s e l l / P l a n n i ng 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 u r b a n i z a t i o n. But w i t h 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. Piera Chen An array of main streets, wide main avenues and/ or breezeways should be aligned in parallel, or not more than 30 degrees to the prevailing wind direction, in order to maximize the penetration of prevailing wind through the district. Height variation should be considered as much as possible with the principle that the height should decrease towards the source of the prevailing wind. The stepped height concept can help optimize the wind capturing potential of the development itself. 3 No. 270 19th December 2005