Air circulation in urban areas

One of the consequences of the dramatic increase in urbanization that has taken place in recent years is the replacement of rural and green areas with roads, vast extents of concrete and large vertical surfaces. The air circulation in urban areas is different from that in the surrounding rural environment and is difficult to predict because it largely depends on the arrangement of buildings and streets, the presence of vegetation and other topographic features. In order to improve our understanding of wind field in cities, field measurements, laboratory-scale physical modelling and numerical simulations have been widely used during the last decades. We address this subject providing a summary of the present knowledge of air circulation in urban areas. The most common flow topologies encountered in urban canopies are described, which include archetypal simplified geometrical configurations such as the isolated building, street canyons, groups of buildings and street intersections.