The Oasis Effect Concept in Hot Desert Climate Cities: Densifying and Compacting Around Metro Stations to Enhance Pedestrian Comfort

Abstract

Nowadays, the cities in which we are living are complex, energy-consuming, and polluting systems. Radical changes since the last century have happened as a result of the automobile introduction and the oil boom. Moreover, one of the essential factors that influence microclimate is urban morphology. Streets, as they are a substantial part of urban open space, play a significant role in creating the urban microclimate. Street geometry and orientation affect the amount of solar radiation received by street surfaces. Outdoor thermal comfort in hot desert-climate cities depends on solar radiation. Under low latitude conditions, the minimization of solar radiation within the urban environment may often be a desirable principle in urban design, and the urban fabric of old compact Islamic cities reflects that. Jeddah is a city located in the western part of Saudi Arabia, at latitude 21° 32' north. The city is expected to start constructing a subway in 2020. Therefore, that is likely to change the behaviors of its inhabitants drastically.

This study aims to extract concepts from the old compact area to develop an outstanding future strategic compact morphology that would facilitate the dynamic development of the city. Considering the main stations of the future metro as nodes creating more densely inhabited fabric around them would provide transitional spaces for pedestrian activities. The concept is to provide an 'oasis effect,' mainly attributed to shading. Microclimate generated in and around these activity nodes must be mainly well designed to encourage residents and visitors to reclaim a pedestrian life that was noticeable in the old city, but has virtually disappeared in newer neighborhoods, entirely devoted to automobile transport. Services and facilities around metro nodes should become the transitional thermal comfort areas of the metro station exits.

The paper provides an overview of the old Islamic cities' morphology located at low altitudes. It evaluates the characteristics of the old urban fabric of Jeddah city through graphical analysis of the street geometry, orientations, and calculating the built-up density. Four different density indicators have been calculated (FSI), (GSI), (L), and (OSR).  Furthermore, simulations that are used to assess the incident solar radiation in the old urban layout by the software "Heliodon 2" (direct shortwave, Sky View Factor) "Heliodon plus" (climatic data), describe the quantitative distribution of incident radiation on the canyon and facades enabling us to identify specific aspects.

The findings illustrate the implications of the old layout. It shows that the existing morphology significantly undermines the intensity of solar energy and solar access time interval in summer and winter on the horizontal surfaces (canyons) and vertical surfaces (walls). The results provide some helpful insights for the planning of a high density and compact 'Oasis effect' around the metro nodes.