Wind Tunnels and "Hotspots"

In centuries gone by, town dwellers were sheltered from the wind by closely spaced buildings of roughly uniform height. Streets were narrow, as movement was mostly on foot. High-rise development and wider roads for cars have brought big changes to the wind environment of our cities, not always for the better.

The impact of a high-rise building on the wind speed at street level depends on its surroundings, as well as on the building itself. Where many closely spaced tall buildings of similar heights are already built, adding one more may have little impact. However, the addition of a building which juts well above the roof level of surrounding buildings will result in air flowing down the exposed windward face of the building, with increased speed at street level. The comfort (use of pavement cafes, window-shopping) and even the safety of our streets can be affected: elderly pedestrians have been blown off their feet and killed because of strong gusts around tall buildings.

Winds around a proposed new building can be estimated from the wind climatology of the region, using the results of wind-tunnel tests showing airflow around a scale model of the building. Any problems can be addressed by design details such as canopies at the base of buildings, which shelter pedestrians from the downward rush of air. One North American city has innovative zoning laws, designed to prevent wind problems. The allowable building heights decrease evenly with distance from the city centre, so that the building height zones form concentric circles. Since new buildings are usually built to the maximum allowable height, eventually no building in the city will have a height much different from its neighbours. In time, wind disturbances due to tall buildings in this city will dwindle and vanish.