Evaluate the thermal performance of green roofs as an urban heat island mitigation strategy under arid climate conditions in Bahrain

Abstract

Purpose This study aims to evaluate the thermal performance of green roofs as an urban heat island mitigation strategy under arid coastal climate conditions by using Bahrain as a case study. Design/methodology/approach A scenario-based parametric simulation study was conducted using ENVI-met v5.7.1. Eighteen green roof scenarios were developed by varying key parameters, including leaf area index, plant height, substrate thickness and soil moisture. The simulations were validated against field measurements and compared with a conventional bare roof configuration under extreme summer conditions. Findings Results indicate that, under peak daytime conditions (12:00), green roof scenarios reduced roof surface temperature (Ts) by approximately 28.5–29.3°C relative to the conventional bare-roof reference case. By contrast, reductions in near-roof air temperature (Ta) at 2 m above the roof were considerably smaller, ranging from approximately 0.2°C–0.8°C relative to the bare roof. The results further show that substrate moisture is the dominant factor influencing green roof thermal performance, whilst variations in leaf area index and plant height produced smaller incremental differences between green roof scenarios. Practical implications The findings provide guidance for climate-responsive green roof design in arid environments, highlighting the critical role of irrigation strategies and vegetation selection in achieving optimal thermal performance. Social implications This study demonstrates how green roofs can moderate harsh microclimatic conditions in Bahrain's dense urban areas. The resulting temperature reductions contribute to improved outdoor thermal comfort, reducing heat stress risks for pedestrians and roof users. Common implementation supports healthier and more liveable communities by introducing greenery into highly built-up neighbourhoods lacking natural shading. The findings also highlight the need for sustainable water-use practices, stimulating community-level discussions on balancing cooling benefits with responsible irrigation. Overall, green roofs can support long-term public health resilience and strengthen social adaptation to rising temperatures in arid Gulf cities. Originality/value This study contributes to the limited body of research on green roof performance in arid coastal climates by combining scenario-based parametric simulation and validation to identify key design parameters influencing rooftop cooling efficiency.