Relation of geometry, vegetation and thermal comfort around buildings in urban settings, the case of hot arid regions

Abstract In the cities of the arid regions, sun and light are the most crucial dimensions and the most important ones in the assessment of the quality of environment in urban external spaces. They can generate, depending on their magnitude, a momentary embarrassment or a daily permanent stress, likely to condition the relations of the man with his entourage. The inhabitant of these cities and these spaces develops a whole arsenal of behaviours to adapt to it. They go from the simple embarrassment to social isolation. The daily practice of urban space is inevitably disturbed. The public streets and places are among the features in which the quality of environment and comfort have come to deterioration. This degradation is due mainly to a discontinuity in the use of these spaces: the hours of frequentation correspond to the freshest hours of the day, with the result that during the long summer period, which spreads out from May to October, the majority of these spaces witness a drastically reduced frequentation. This fact encourages us to try to better understand how urban external space is affected by the climate and especially how it acts on this one in return. In the majority of the cities of the hot climate areas, the dominating role and the importance of the places are characteristic of a way of life which is not limited inside the buildings. The intrinsic potentialities of these spaces transform them into places of relaxation, meeting and allow a great number of activities. In these hot climates, in order to fight against certain excessive situations, the recourse to natural means was essential through the centuries. The recent urban transformations, by inducing a generalised mineralisation of urban external spaces, often synonymous with summer overheating, make necessary the recourse to thermal regulation techniques. Moreover, these urban spaces are, in most cases, adjacent to occupied spaces like housing, administrative and commercial premises and may, therefore, add to their cooling load by transmitting excessive heat to the surrounding premises. That is why it seems necessary to understand the way they receive the solar radiation and the influence of geometry, orientation and other factors by means of calculating solar energy, ambient and mean radiant temperatures. The objective of this paper is to show that the thermal regulation of the urban microclimate, in hot and dry climate areas is possible by judicious choices of the orientation of the place, space form, size and provision and importance of the vegetable masses.