Microclimatic interaction in semi-humid environments: Quantification of the urban heat island, shading efficiency, and their impact on the humidex heat stress index. Case study: Souk Ahras City, Algeria

Abstract

The urban heat island degrades public health and outdoor thermal comfort by exacerbating extreme heat conditions within urban environments, especially during heat waves. This study examines these effects and shading effectiveness in Souk Ahras using a tripartite geographic gradient (rural, suburban, and urban) to evaluate both urban and intra-urban thermal impacts. Specifically, the study quantifies the urban heat island intensity by calculating the diurnal temperature differences through a rigorous in situ approach, while assessing the Humidex heat stress index at sunny and shaded locations. The results indicate that the peak intensity of the urban heat island was recorded at 14:00. At this hour, the urban heat island intensity, calculated relative to the rural station, reached 3.7 °C, while the intra-urban urban heat island showed an average maximum temperature difference of 2.0 °C. This confirms that Souk Ahras is affected by the urban heat island phenomenon, which has a quantifiable effect on outdoor thermal comfort. Based on the difference in Humidex values of 5.1 points between locations A and B, and 3.46 points between locations C and D, tree shade is an effective strategy for reducing heat stress and enhancing outdoor thermal comfort.