Street Morphology Research Articles

Geometry and orientation aspects in passive cooling of canyon streets with trees

As streets usually cover more than a quarter of the urban area, canyon street morphology plays an important role in creating the urban climate. It directly influences the air temperature, moisture and wind flow within the streets as well as the urban surrounding area and has been the topic in several urban climatology studies. Recently, studies based on the street cluster thermal time constant (CTTC) model have been carried out by the authors with a view to assessing the thermal effects of alternative architectural designs of the flanking buildings and inner courtyards. The effect of green spaces, especially that of shade trees which plays a significant role in solar radiation penetration, has not yet been considered. In the CTTC model, passive cooling of the street by solar heating attenuation is governed mainly by the street orientation and its geometry as measured by the aspect ratio of flanking buildings height to street width. The tree shading coverage largely offsets the contribution of these two factors. Moreover, significant thermal effects are provided by the tree canopy, in addition to the direct solar radiation. Accordingly, adjustments are called for in the currently used canyon street models. The present paper discusses the geometry and orientation aspects of the canyon street climate and how these aspects are affected and can be reconciled in the presence of shade trees. Some consequences of environmental design of urban spaces and their effects on outdoor thermal comfort are also considered.

GATES AS SIGNS OF AUTONOMY IN MUSLIM TOWNS

sion with Oleg Grabar about the Muslim built environment. He advised me to investigate the word khatta and its exact meaning and implication for Muslim towns. That advice gave me a key for future essays, among them this study. Most of the works that have dealt with gates have concentrated on monumental portals such as those to cities and mosques; they range in theme from semiotic interpretations to the geometric innovations of their builders. Gates to shared residential spaces such as dead-end streets have been neglected by historians, mainly because they are not attracted to gates that are neither as elaborately nor as elegantly built as monumental gates are. Here I will argue that residential gates play a role as symbols of control in society and deserve attention because they can contribute to the understanding of the sociocultural structure of societies where they are found. Contemporary scholars have been misled in their observations of the morphology of streets in Muslim towns; they describe them as either a labyrinth of thoroughfares and alleys, or as they exist today a network of linear streets organically arranged. But in the past there were gates all over the city that divided this labyrinthine space into many smaller spaces for the exclusive use of particular groups. These places closed in by gates had a function that has been lost today and that affected many aspects of city life. The same traditional physical organization had a totally different quality than that we see