Effects of street tree configuration and placement on roadside thermal environment within a tropical urban canyon.

The Urban Heat Island (UHI) effect increases surface and air temperatures, affecting urban health and well-being. A well-known UHI mitigation measure is the increased roadside tree vegetation facilitating evapotranspiration and shade. In its implementation, the identification of thermally optimal street tree configurations and a quantitative assessment of how various street tree configurations impact the roadside thermal environment were deemed essential and were chosen as the main aims of the study. Twelve tropical urban canyons were categorized into three clusters representative of different street tree placement and configuration scenarios. A control cluster devoid of any roadside trees was also selected. The CFD-based 3-D microclimate model 'ENVI-met' was used to identify suitable roadside urban tree planting scenarios for better microclimate regulation. From a tree planting scenario analysis done as part of the study, the greening scenario of using a 'Continuous tree row (Densely foliated - high Leaf Area Density - LAD)' tree configuration was recognized with the highest ambient temperature reduction of 1.41 °C. The study outcomes reveal that tree configuration of high LAD street trees placed in closer spacing contributes towards the better cooling effect of roadside environments and thus improves thermal comfort for warmer tropical climates of higher humidity levels. The study's findings offer valuable insights for urban planning professionals and policymakers involved in designing future cities and urban developments. They emphasize the importance of strategic tree-planting designs and configurations to enhance thermal comfort and livability in urban areas. This highlights the need to avoid ad-hoc procedures and instead prioritize well-planned roadside tree configurations within urban canyons.