Microclimatic analysis of "compact" urban canyons in an arid zone

While the modifying effects of a city's surface on its climate are well doc umented, there remains a need for useful micro-scale analyses of thermal co mfort conditions which may be applied to urban design. In the present study , empirical data taken from extensive full-scale measurements in a number o f low-rise urban street canyons in the arid Negev region of Israel are inte grated with an energy-balance model representing the thermal exchanges betw een a pedestrian and the street canyon environment. Analysis of microclimat ic parameters and overall energy balance suggests that in summer, overheati ng within the canyon is sensed primarily as a nocturnal phenomenon, and tha t during hours of substantial heat stress in a desert climate, the compact canyon is in fact a potential "cool island", mainly due to internal solar s hading. In winter, a compact geometry was found to provide relatively warm conditions, with the key Factor being protection from strong winds during c old night hours. (C) 1999 Elsevier Science Ltd. All rights reserved.