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This study aim to delineate an urban planning metric for greenery called the green plot ratio (GPR), is based on a common biological parameter called the leaf area density (LAD), which is defined as the portion of the single-side leaf area per unit volume of tree canopy. The study will investigate the effectiveness of GRP for urban greenery to maximize cooling benefits and potentially improve the daytime heat effect. Four climate-sensitive areas for tree planting with different Bangkok’s urban morphologies are evaluated through an urban micro-climate simulation performed by the ENVI-met model. Simulation results indicated that the cooling effect of GPRs is highly associated with urban form. Maximum air temperature reduction (a 1.2 ◦C reduction at the pedestrian level) is the most profound for the very high-density urban form on summer diurnal range of tropical climate, whereas the average air temperature vary linearly is reduced during the peak heat of day by 0.02°C–0.12 °C by increasing GPRs. These findings will help urban planners offer better guidelines for planting and establishing urban trees to mitigate extreme heat in the hot-humid tropical environment.
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