AIR VENTILATION IN CITIES WITH DENSE HIGH-RISE DEVELOPMENTS AND COMPLEX TOPOGRAPHY

With the ever growing population in the world, cities everywhere are building more taller buildings and more densely developed building complexes. As a result, pedestrian level air ventilation in the inner city areas can be very poor. Especially during the summer months cities situated in the warmer regions could suffer from hot spells and without adequate ventilation, pedestrian environment could become un-healthy and un-tolerable.

Wind flow inside the city area is affected by many factors. Broadly speaking, there are two major issues to be considered. One is the amount of wind available to the city, i.e. blowing onto the out skirt of the city; the second is the modification of the available wind by building developments. Many cities are situated in locations with prominent topographic features, for example, mountains, slopes and valleys. These topographic features have a strong effect on the wind flow pattern and can reduce the 'available wind' by it significant amount. With the available wind, the overall building development of it region and the local configuration of building complexes will further modify the wind flow patter and wind strength of a location.

This paper carried out studies on the two issues. The effect of topographic features on wind flow pattern was investigated. The blockage effect of mountain and mountain range and the funnelling effect of valley were studied. The changes in speed and direction of the available wind were investigated. The study on the effects of building developments and building complexes on wind flow were next studied. There was the overall effect of buildings in a region affecting the general wind characteristics, for example the increase in terrain roughness due to tall buildings resulting in the slowing down of the wind at downstream areas. Locally building blocks and podiums would affect the air flow pattern around the locality. The effect of their configuration on air ventilation was investigated. Finally, mitigation measures to improve air ventilation were proposed in the paper.