Evaluating and Improving Outdoor User Thermal Comfort at Sacred Sites in Saudi Arabia with Reference to Arafat Mountain Area

Abstract

The rapid growth of urban populations and the expansion of city infrastructures in recent decades have intensified climatic challenges, worsening outdoor thermal comfort, restricting pedestrian activity, increasing energy demands and posing risks to human health. Such climatic pressures can be more critical in hot, arid climates, where extreme heat and intense solar radiation significantly affect users’ thermal experiences in open spaces. Understanding and enhancing the thermal performance of such spaces is therefore essential, particularly in Makkah, Saudi Arabia. Makkah is a holy city with exceptional significance in the Islamic world; it hosts millions of pilgrims annually. Despite the city’s global importance, research systematically evaluating its outdoor thermal environment has been limited. This study evaluates the existing outdoor thermal comfort of a sacred site in Makkah’s hot, arid climate, i.e. the Arafat Mountain area, and investigates mitigation strategies to improve its microclimatic conditions. Field measurements were conducted over continuous 24-hour periods in winter and in summer to capture meteorological data under each season’s conditions; these included air temperature, relative humidity, wind speed, globe temperature, global solar radiation and ground surface temperature. The measured data assisted in developing a high-resolution model using the ENVI-met simulation tool. The model was validated against the field measurements, and sensitivity analyses were applied to ensure that the model reflected the site’s actual environmental characteristics. The validated base model was used to simulate existing conditions and a series of proposed mitigation scenarios: nine vegetation scenarios, three involving the use of cool materials, six structural shading scenarios, eight for water spray systems, and a combined scenario integrating the optimal design from each category. The performance of each scenario was evaluated by comparing hourly and daily average outputs against the base model, focusing on their influence on air temperature (AT), mean radiant temperature (MRT) and the universal thermal climate index (UTCI). The findings revealed that vegetation significantly improved daytime AT, MRT and UTCI, with higher tree densities and evenly distributed layouts providing the greatest benefits (peak UTCI reductions of up to 4.96°C in summer and 3.1°C in winter). Cool materials were ineffective due to their tendency to increase reflected shortwave solar radiation, resulting in a deterioration of outdoor thermal comfort; although summer mean AT was reduced by 1.18°C, MRT and mean UTCI increased by 4.54°C and 0.22°C, respectively. Structural shading reduced daytime outdoor thermal comfort in summer (peak UTCI reductions of up to 4.45°C) but increased overall thermal comfort in winter (mean UTCI increases of +1.85 to +2.05°C) and at night, as longwave radiation was trapped under the structural shading canopy. This highlights the diurnal and seasonal limitations of structural shading. The application of a water spray system proved the most effective single measure, particularly in summer, lowering AT and UTCI without increasing MRT (mean UTCI reductions of 3.19°C in summer and 0.82°C in winter). The combined scenario outperformed all individual strategies in summer, achieving the largest improvements across all thermal variables (mean UTCI reduction of 5.2°C, with peak hourly reductions ranging from 4.88°C to 9.82°C) and substantially lowering the number of hours of extreme heat stress (from eight hours in the base model to three hours). In winter, although the daily mean UTCI increased slightly due to higher nighttime values, midday thermal improvements were significant (UTCI reduced by up to 3.04°C), effectively eliminating peak strong heat stress conditions (from two hours in the base model to zero). Overall, this study increases understanding of how different mitigation strategies perform under Makkah’s seasonal climatic conditions, emphasising the importance of integrating multiple mitigation strategies to improve outdoor thermal comfort in such hot, arid climates. Collectively, these strategies minimise thermal stress during critical daylight hours and offer greater resilience solutions than do individual strategies. The study reinforces that the use of combined mitigation strategies would improve outdoor thermal comfort and consequently enhance Makkah’s liveability by increasing the usability of its outdoor spaces and potentially lowering health risks. The findings establish a framework for climate-sensitive urban development in hot, arid regions such as Makkah. They highlight the value of adaptable, flexible and multi-strategy approaches to outdoor thermal comfort in improving urban resilience, especially in intense heat conditions.