Comparative review of urban geometric parameters and their uses in outdoor thermal environment studies

Abstract

A significant proportion of the world's population is currently experiencing heat stress. This results from the effects of global warming, urban heat islands (UHIs), and the growth of urban populations. Researchers have investigated multiple strategies to address this problem. It has been found that the outdoor thermal environment (OTE) can be modified by means of vegetation, water surfaces, and urban geometry. Several studies have indicated that certain geometric factors have demonstrated a higher degree of effectiveness in cooling the surrounding environment. OTE studies often employ two commonly utilised factors, known as urban geometry indicating parameters (UGPs)—the sky view factor (SVF) and height-to-width ratio (H/W). This article compares OTE studies focusing on these two factors. The comparison encompasses characteristics such as study methods, places and times of conducting, and thermal indices. The findings indicate that geometric studies have primarily relied on simulation and field measurement methods. These studies were predominantly conducted in tropical or subtropical cities during warm seasons, with a preference for daytime investigations. Complex thermal indices, including the physiologically equivalent temperature and mean radiant temperature, were commonly employed. In addition to UGPs, other physical factors, such as orientation, were also taken into consideration. Studies on H/W and SVF differed slightly although they are both geometrically indicative. This review can provide guidance for future studies in the field of urban geometry, in that researchers may choose to prioritise the examination of practical indicators, such as the energy load, to conduct a more comprehensive analysis while also taking into account other physical aspects, such as the presence of trees.