Reducing urban heat stress through green roofs: a modeling-based performance analysis across green roof types and urban morphologies

Rising temperatures driven by climate change and rapid urbanization have heightened the need for effective urban cooling strategies. Green roofs, as nature-based solutions, can offer a practical alternative contribution in dense urban areas by improving thermal comfort. However, accurately modeling their microclimatic impact remains difficult due to a large variety in green roof design parameters and limited validation of available tools. In addition, few green roof modeling studies account for urban morphology at the block scale. This study addresses these gaps by validating the green roof module of the Solene-microclimat urban microclimate model with a comparison against measurements and by conducting a local sensitivity analysis of the green roof parameters. The green roof model outcomes were compared to measurements and found to depict physical processes correctly. A local sensitivity analysis investigates how substrate and vegetation parameters as well as irrigation factors affect pedestrian level thermal comfort across nine
representative urban morphological archetypes in Liège, Belgium, during a hot summer day. Results show that while irrigation and vegetation characteristics influence outdoor thermal comfort, substrate properties have minimal impact. Well-irrigated, tall, and dense green roofs were found to reduce average pedestrian air temperature by up to 1.4◦C, compared to average scenario green roof. Additionally, green roofs are most effective in improving pedestrian comfort when green roofs are clustered and located near walkable pedestrian areas. The compact mid-rise + low-rise archetype is found to maximize the benefits of green roofs.