Heat stress in social housing districts: tree cover–built form interaction

As global warming increases, understanding the vulnerability of urban areas to extreme heat becomes crucial. Social housing districts, due to their urban form and demographic composition, are identified as high-risk areas for heat stress. This study investigates the impact of trees on mitigating outdoor heat stress in social housing districts, focusing on the Mediterranean region, particularly the metropolitan area of Barcelona, Spain. Using mean radiant temperature (MRT) as a key parameter, simulations were conducted to assess the influence of trees on heat stress in two districts differing in building types: linear blocks versus towers. The results show that the absence of trees makes towers more vulnerable to heat stress, as they lack long-term shaded spaces, such as the corridors in the linear blocks. In contrast, when trees are considered, tree-induced shading significantly decreases MRT and shifts its distribution pattern so that both urban fabrics exhibit similar performances, achieving the same percentage of open space with moderate heat stress (22%). These findings underscore the importance of a performance-based design approach, emphasising the need to consider both urban form and tree cover for effective heat stress mitigation in social housing districts. POLICY RELEVANCE Shade planning plays a key role in shaping thermal comfort outcomes under heat-stress conditions. Urban fabrics with high open space ratios, typical of the European post-war modernist social housing boom, are especially vulnerable to this issue, underscoring the importance of integrating vegetation as a key component of green infrastructure and a critical microclimatic resource. This work emphasises the need for planning frameworks that recognise trees not only as design elements but also as essential urban infrastructure. By leveraging workflows compatible with geographical information system (GIS)-based tools used by urban practitioners, the study supports both the design and the management of green infrastructure through actionable, context-sensitive, heat-mitigation strategies. By enabling the identification of critical shade providers and assessing their performance under different morphologies, such tools can guide adaptive strategies, from tree placement to irrigation prioritisation, enhancing the resilience of urban environments to rising heat stress.