Urban climatology in arid regions: current research in the Negev desert

Abstract

Abstract:Desert cities provide climatologists with circumstances that can be qualitatively different from those encountered in more temperate environs. These distinctions are expressed in the balance of heat and moisture between a dry atmosphere and an urbanized terrain, and they are experienced by city dwellers in urban outdoor spaces. But, while such places are characterized by harsh thermal extremes, they also present unique opportunities for microclimatic enhancement.This potential has motivated a series of studies in the arid Negev region of Israel, beginning with a measurement campaign showing that a dense urban fabric can provide significant thermal benefits due to protection from solar radiation, which is dominant within the overall energy exchange. To generalize these findings, an innovative modelling approach -using an open-air, scaled urban array -was used to study variations in urban geometry under realistic radiative loading and boundary-layer turbulence. The surface energy budget above this small-scale urban canopy was found to be similar to observed energy exchange patterns of actual cities.Measurements within the scaled urban canyons served as input to a pedestrian-centred energy exchange model, and a semi-empirical model was also developed for predicting pedestrian energy exchange and thermal discomfort as a function of urban attributes and meteorological data for a given land-use area.This integrated modelling approach revealed that increased urban density, while serving to increase radiative trapping and storage of heat within the urban fabric, also reduces pedestrian thermal stress during the critical daytime hours. This 'cool island' effect is enabled by the high thermal inertia of the built-up area, and the sharp diurnal fluctuations that are peculiar to a hot-arid climate. Its impact is contingent, however, upon the orientation of the street canyon in question -increasing as street-axis orientation approaches north-south and becoming negligible in the east-west direction.

Review of urban climate research in (sub)tropical regions

“…The available work is primarily concerned with the influence of the built form (geometry, height-to-width of street canyons) to promote ventilation, building materials and colour as means to reduce the absorption of solar radiation and storage of heat as well as the role of vegetation for shading and evaporative cooling to moderate the thermal and moisture climate. Studies were conducted in the following climate types and cities: (1) equatorial wet Colombo (Emmanuel, 2003(Emmanuel, , 2005aEmmanuel and Johansson, 2006), Sao Paolo (Ribeiro, 2005) and Singapore (Wong et al, 2003;Wong and Yu, 2005;Chen and Wong, 2006), (2) tropical wet/dry Belo Horizonte (Sad de Assis and Frota, 1999), (3) tropical highland Mexico City and (4) subtropical dry San Juan, Argentina (Papparelli et al, 1996), Gaborone (Jonsson, 2004), Fez, Marocco (Johansson, 2006), various cities in Algeria (Ali-Toudert et al, 2005;Ali-Toudert and Mayer, 2006), Dimona, Israel (Pearlmutter et al, 2007a) and various settlements in the Negev desert of Israel which are reviewed by Pearlmutter et al (2007b) with special attention given to the relationship between urban geometry and thermal stress.…”

Impact of shade on outdoor thermal comfort—a seasonal field study in Tempe, Arizona

“…Urban areas are heterogeneous and encompass various urban forms (type, density, and arrangement of buildings), surface materials, and landscapes, creating local scale and microscale climates that vary widely across space and time (Erell et al 2012; Stewart and Oke 2012; Middel et al 2014). Several studies have investigated thermal comfort in the context of urban form, focusing on street canyons or sky view factor (Johansson and Emmanuel 2006; Ali-Toudert and Mayer 2007; Pearlmutter et al 2007; Mayer et al 2008; Lin et al 2010; Holst and Mayer 2011; Lee et al 2014). Although the relationship between thermal comfort and the built environment tends to be strong, environmental factors, including meteorological conditions, generally only account for half of the variance in thermal sensation (Nikolopoulou et al 2001; Nikolopoulou and Steemers 2003).…”

Hydrological extremes in hyperarid regions: A diagnostic characterization of intense precipitation over the Central Arabian Peninsula

“…Clustering, large fluctuations and long quiescent dry phases represent in turn a major ecological forcing, shaping and driving the ecosystems and the sustainable development of hyperarid environments [Sharon, 1981;Dickman, 2003;Warner, 2004;D'Odorico and Porporato, 2006;Sen, 2008;Peters and Neelin, 2009;Nicholson, 2011;Rosenzweig et al, 2011]. The link between aridity and sustainability has become increasingly important in the last decades, as urban development in desert regions approached a quasi-exponential growth [Carpenter et al, 2005;Pearlmutter et al, 2007;Reynolds et al, 2007]. Although the absolute contribution of precipitation from arid regions to the global hydrological cycle can be easily dismissed as marginal, its hydrological impacts are undeniably more grievous than in temperate climates, as testified by the increasing number of human losses and material damages following intense precipitation over the Red Sea coast of Saudi Arabia [EM-DAT, 2014;Al Saud, 2010;Pedgley, 1974;De Vries et al, 2013], the Levant [Greenbaum et al, 1998;Krichak and Alpert, 1998;Krichak et al, 2000;Dayan et al, 2001;Ziv, 2001], and the Arabian Gulf regions [Membery, 1997;Zhang et al, 2005;Al Sarmi and Washington, 2014;Sherif et al, 2014].…”