By Professor Ren Chao
The past week has seen the return of summer thunderstorms, and while that may be a relief from the sweltering heat, one cannot escape the feeling that each year is warmer than the last. Indeed, 2017 is set to be the hottest year on record, according to recent news reports.
Cities worldwide are heating up as they get more crowded and built up. In mainland China, many cities that underwent rapid urbanisation were built haphazardly. They have seen tall buildings mushroom in a relatively short period. These building clusters are often densely packed around a core of industrial ventures and over a cobweb of makeshift roads built for short-term needs.
Such high-density building clusters have created pockets of “urban heat islands” in cities, where the average temperatures rise significantly above that of the surrounding environment. Without allowing sufficient room for ventilation, wind circulation inside these city blocks is often sluggish, if not altogether stagnant.
During humid seasons, hot air, together with the pollutants it traps, builds up into smog, causing discomfort and health risks to inhabitants.
In mainland China, the building of ventilation corridors has become an almost default option for city administrations responding to poor air quality. Ventilation corridors are passages in the form of landscaped areas, main roads, connected recreational spaces, or low-rise buildings, which enable air to flow freely through cities.
Yet, a mass adoption of wind corridors to ventilate cities without due appreciation of the variations and possibilities in each local case is not effective. What should be prioritised are, instead, urban ventilation assessments.
Officials, planners and decision-makers have to understand and assess the urban wind environment in each different location, as well as the planning, implementation and control of air paths, in order to create “breathing cities”.
Cities are engines for economic growth, but they should also be seen as organic entities, which need to “breathe” to keep natural ventilation in urban areas.
To “breathe”, a city needs to be equipped with an effective ventilation system through proper landscape design, careful land use allocation and clear planning strategies, so that cool and fresh air can be transferred from rural areas to downtown. At the same time, air pollution dispersal can be more effective.
The mechanism is similar to the human lung’s rhythmic sequence of inhalation and exhalation. The essence of a breathing city lies in its ability to harness wind as a natural resource that circulates within it effectively.
In building a “breathing city”, planners need to assess the natural environmental sources and key direction of wind, taking into consideration its topography of hills, water bodies and woodland. With these data, roads, streets and buildings may then be designed and laid out in a pattern that allows efficient circulation of wind for exchange of air between the city and the surrounding region.
Implementing these “breathing city” features, the improved wind circulation within city blocks should ameliorate the “heat island” effects and help disperse air-borne toxins, pollutants and greenhouse gas.
It should be stressed, however, that the “breathing city” approach to urban planning is not a panacea for solving the problem of air pollution or addressing air quality issues. If the air that is drawn in to ventilate a city is polluted to begin with, it will not necessarily make much difference to the air quality.
Fundamentally, air pollution emission source control remains the way to mitigate haze or air pollution. That said, combating air pollution is an issue that requires multi-disciplinary efforts and effective policies at different levels.
A change can be made here by realising that a headlong dive into building wind corridors alone does not nearly hit the crux of the problem. Rather, urban ventilation assessments should form the basis of planning efforts to create “breathing cities” for healthy and quality living.
Professor Ren Chao is with the School of Architecture, Faculty of Social Science, at The Chinese University of Hong Kong.