Alosimi, Turki
(2025)
Environmental design and thermal comfort in urban courtyards within different urban design patterns in Saudi Arabia.
PhD thesis, University of Nottingham.
Abstract
Urban open space design and patterns play a vital role in shaping the microclimate of outdoor environments, significantly influencing user comfort and activities. In a harsh arid environment like that of Saudi Arabia, creating high-quality, thermally comfortable outdoor urban spaces is critical. However, studies have highlighted the lack of detailed policies for the environmental planning and design of outdoor urban spaces in Saudi cities, particularly in Makkah, contributing to increased thermal discomfort.
This research investigates the influence of alternative urban design patterns on the microclimate and thermal comfort of outdoor urban spaces in Makkah, as an example of a city in a hot-arid climate region. Using three types of courtyard at Umm Al-Qura University (semi-enclosed, partially-open with a canopy, and fully-enclosed), the study analyzes key urban design parameters, namely, orientation, aspect ratio, tree coverage, and mist system density and examines their impact on air temperature, RH, WS, mean radiant temperature (MRT) and physiological equivalent temperature (PET). Field measurements were conducted during extreme summer and winter conditions, with meteorological data outside the courtyards recorded for 10 days and microclimatic conditions inside each courtyard monitored for 48 hours. Numerical modelling using ENVI-met software was then used to simulate a series of proposed scenarios (seven for orientation, three for aspect ratio, five for tree coverage, and three for misting), which were then assessed against the base case data to identify the most effective options in each case.
The findings reveal that the impact of the design parameters varies by courtyard type. Orientation adjustments had the greatest influence on the fully-enclosed courtyard, where a 135° rotation reduced daily PET by 0.39°C in summer through improved shading. In contrast, the partially-open courtyard benefitted most from orientation changes that enhanced airflow, reducing PET by 0.15°C in winter. Aspect ratio changes were particularly effective in the semi-enclosed courtyard, where increasing the height-to-width ratio to 0.75 H/W lowered PET by 1.08°C in winter and 0.41°C in summer, due to enhanced shading, without significant airflow restriction. The fully-enclosed courtyard and the partially-open courtyard with the structural canopy benefitted more from the lowest aspect ratio (0.25 H/W), as this enhanced airflow and reduced PET. In winter, the most significant PET reduction occurred in the fully-enclosed courtyard with a low aspect ratio (0.25 H/W), achieving a daily PET reduction of 1.34°C, driven by an increase in WS of 0.66 m/s.
Tree coverage was found to provide substantial cooling across all courtyard types, with 30% coverage reducing PET by 2.34°C in summer and 2.78°C in winter in the fully-enclosed courtyard. The semi-enclosed courtyard experienced a PET reduction of 1.46°C in summer, while the partially-open courtyard with the canopy showed more moderate reductions due to the pre-existing shade. High-density mist systems (2-meter intervals) proved most effective in reducing PET during summer, with the semi-enclosed courtyard showing the largest reduction of 7.61°C, followed by the fully-enclosed courtyard at 6.98°C. However, excessive humidity in enclosed spaces during winter required balancing mist density to prevent discomfort.
These findings are used to develop actionable urban design guidelines for architects and urban designers to promote the efficient use of orientation and aspect ratios to optimise shading and airflow and to ensure that tree coverage and mist systems are utilised most effectively. Recommendations for policy-makers are also provided to create a holistic framework to support the use of urban design to enhance outdoor thermal comfort in Makkah. This research therefore contributes to sustainable urban planning in hot-arid climates by offering practical strategies to reduce thermal stress and mitigate rising temperatures caused by climate change. At the local level it offers solutions to create more comfortable outdoor environments in Makkah and in other Saudi cities, aligning with the goals of Saudi Vision 2030. At an international level, the findings will also be of benefit in other regions which experience similar climatic conditions.
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