Climate change and the urban heat island (UHI) effects are increasing heat stress and adversely impacting outdoor thermal comfort in urban areas. The study demonstrates that thermal comfort conditions can be improved by reducing air temperature and surface temperature with the integration of street trees into the urban environment. In this work, computational fluid dynamics (CFD) simulations using unsteady Reynolds-averaged Navier–Stokes (URANS) equations have been performed to analyze the cooling effect of street trees for heatwave period (18–22 June 2015) in a hot-humid urban environment. The results are then compared in-term-of air/surface temperature, flow-velocity and apparent temperature for the vegetation case, open-space case, and built case. The analysis shows that the vegetation can effectively decrease surrounding temperature (a reduction of 1.2 K), thereby reducing energy consumption and effectively promote thermal comfort conditions. The study findings will encourage city planners and citizens to take action for urban greening.

Computational fluid dynamics has proven itself as a versatile tool to study various urban physics phenomena and develop urban heat island adaptation strategies. This study is based on the development of new parameterization related to aerodynamic and thermal effects of urban vegetation; and their implementation in CFD to study its effectiveness in improving the thermal environment with approximately 100 trees having canopy width/height of 9 m. A more realistic consideration of these parameters is required to improve the quality/accuracy of CFD results. The study results show that vegetation, modeled with these developed parameters (i.e. actual form drag coefficient and variable tree transpiration rate), yields significant variation in micro-climatological results, as causes a reduction of 1.2 K and 0.9 K; 4.0 K and 1.8 K in air temperature and surface temperature respectively. The tree, modeled with the actual form drag coefficient, has highest impact in reducing velocity i.e. upto 0.5 m/sec.

The urban heat island (UHI) phenomenon has become a major concern for city sustainability in the wake of global warming and rapid urbanization. This has resulted in increased heat stress and worsened outdoor thermal comfort in urban microclimates. The study demonstrated that outdoor thermal stress pedestrians can be reduced in single streets by adopting mitigation strategies i.e. cool materials, vegetation, and water bodies. In this paper, computational fluid dynamics (CFD) simulations using URANS modeling for four different scenarios have been performed to investigate the effectiveness of different mitigation measures in hot humid urban climates conditions. The reduction of ambient air temperature and surface temperature characterizing the mitigation (cooling) intensity is examined at pedestrian height and diverse vertical levels. The analysis shows that on its own, water provides the largest reduction in air temperature at pedestrian height (2 °C) and cool materials provide a larger reduction in surface temperature (6 °C). When applied individually, cool materials are the more effective in the vertical direction with a UHI mitigation intensity of 1.5 °C which is then followed by .vegetation i.e. 1.0 °C. Furthermore, the impact (temperature reduction) is more significant when all three measures are combined as a large reduction of 2 °C in air temperature; and 9 °C in surface temperature were observed respectively compared to the reference case.

The urban heat island (UHI) phenomenon and climate change have become the major concerns for city sustainability in the wake of global warming and rapid growth in urbanization. This has resulted in increased intensity of heat stress and worsened outdoor thermal environmental conditions in urban microclimates. Water bodies are among the most effective means to alleviate the UHI and improve the thermal environment of urban microclimates. The thermal comfort conditions are observed at the pedestrian's level in a horizontal direction and at different vertical levels by assessing the reduction in three variables: ambient air temperature, surface temperatures, and alteration of flow velocity. The water body model used in this simulation is first validated using the sub-configuration method by replicating a previous experimental study. Two different scenarios (one with a realistic setting and the other with a representative water body) were studied and the results show that, for isolated streets, the water bodies can effectively improve thermal comfort conditions by reducing ambient air temperature (i.e. a reduction of 0.9 °C) and surface temperature by 3.5 °C, thereby reducing energy consumption. Moreover, a significant increase in wind velocity was also observed reaching its maximum value at peak times of thermal stress.