Mitigating urban heat island effects using trees in planters with varied crown shapes

Urban downtown areas are often overheated and contribute to the creation of urban heat island (UHI) phenomenon. Implementation of trees is considered an effective way to mitigate UHI and improve outdoor thermal comfort (OTC) in densely built-up areas. This study aims to investigate the potential of applying additional trees in planters to mitigate UHI effects and improve OTC in open urban areas. Simulation of OTC is performed for hot summer days using Universal Thermal Climate Index (UTCI). In this study, we have devised a method to determine favourable locations for a predetermined number of additional trees, with different crown shapes (cylinder, sphere and cone), to improve OTC conditions. In the proposed method, an evolutionary algorithm based on natural selection was used as it is effective for solving problems that have a large number of combinations. The method considers the geometry of the built environment, the geometry, locations and number of additional trees, weather data and UTCI simulation. The method was applied to three different urban morphologies located in the downtown of Novi Sad, Serbia. The results show that, depending on urban geometries and morphologies, different crown shapes lead to different UTCI reduction. Cylinder-shaped and sphere-shaped tree crowns showed to be the most effective in reducing heat stress. The positioning of additional trees reduced the UTCI values at single manikin locations by up to 6.11 °C, indicating that the process of determining their locations is crucial for mitigating the heat and improving OTC conditions during hot summer days.