Blue–Green Infrastructure Strategies for Improvement of Outdoor Thermal Comfort in Post-Socialist High-Rise Residential Areas: A Case Study of Niš, Serbia

Urban densification in post-socialist cities has led to the loss of open and green spaces in high-rise housing areas (HRHA), exacerbating urban heat and reducing outdoor thermal comfort (OTC). This study examines the effectiveness of blue–green infra-structure (BGI) interventions in improving OTC within an infill HRHA courtyard in Niš, Serbia, during the extreme summer heatwave of 2024. A 24-hour field campaign conducted on 14 August 2024 provided data on air temperature, humidity, wind speed, and mean radiant temperature, which were used to validate an ENVI-met mi-croclimate model. Four scenarios were simulated: S0 (existing conditions), S1 (grass), S2 (grass + deciduous trees), and S3 (S2 + shallow reflecting pool). The results show that OTC across all open space areas was extremely poor during most of the day, with acceptable conditions only in the early morning hours. Greening and tree-planting measures produced negligible improvements in thermal comfort, while modifications of surface materials demonstrated slightly higher efficiency in reducing heat stress. These findings highlight the limited microclimatic effectiveness of small-scale sur-face-level interventions and emphasize the importance of integrated urban greening strategies within HRHA regeneration processes.