Urban heat mitigation: A multi-scenario evaluation of cool and green envelope strategies across Hot Desert climate

Cities are experiencing intensified warming due to rapid population influx and the resulting demand for residential and commercial infrastructure. This urban expansion increases air temperatures relative to surrounding areas, known as the urban heat island effect. While many studies have examined different urban mitigation strategies to reduce urban air temperatures, few have simultaneously addressed their effects on outdoor heat index. This study broadens the scope by evaluating these urban mitigation strategies not only for air temperature reduction but also for their influence on outdoor heat index. Three major Saudi Arabian cities with unique climate characteristics were selected, representing the most populous cities. Ten scenarios were tested for each city and season, including cool walls, cool roofs, green roofs, and their combinations. Regional-scale atmospheric modeling was used to estimate outdoor air temperature changes. The cool materials consistently outperformed the green roof. The scenario with 90% reflectivity on the roof and 50% reflectivity in the wall achieved maximum air temperature reductions of up to 4 °C. The results also show that these cooling strategies have the potential to reduce the occurrence of Extreme Caution heat index conditions by up to 68% in certain cases. The results also showed that the irrigated scenario of a green roof was less effective in a humid city compared to the non-irrigated option.