Numerical study of vegetation effects on thermal comfort for outdoor spaces at a public school in hot and arid climate

School outdoor spaces are important for students as they impact learning outcomes, physical and mental health, social interaction, and overall well-being. In hot, arid climates, the use of outdoor spaces becomes a challenge. The high levels of thermal stress impact outdoor thermal comfort during the warmer months, leading to limited or no use of those spaces. This paper assesses vegetation as a passive cooling strategy for an elementary public school in the city of Riyadh, Saudi Arabia. Air temperature (Ta), mean radiant temperature (Tmrt), and Universal Thermal Climate Index (UTCI) are used to investigate outdoor thermal comfort. The experimental approach adopted in this study compares a base model against eight scenarios, which simulate different vegetation (grass, shrubs, two trees at two different heights, 5-10 m) and spacing between them (3.5 m and 7 m). The data is simulated using Envi-Met 5.5 and assessed for their impact on thermal stress levels for the school outdoor space. The results found that by applying trees 10 m high with 3.5 m spacing between them and using evergreen type leaves, Ta was reduced between (1.4-3.2)°C reaching max reduction in August, Tmrt (7.13-64.73)°C where max reduction was recorded in October, and UTCI at (3.00-17.95)°C in April. Therefore, the study offers solutions for existing schools or future ones to enhance outdoor thermal comfort.