©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(5): September 2023 247 Arboriculture & Urban Forestry 2023. 49(5):247–267 https://doi.org/10.48044/jauf.2023.016 island (UHI) phenomenon (Oke 1982). In turn, a greater UHI effect worsens heat waves and heat stress caused by climate change (Mazdiyasni et al. 2019). Higher urban temperatures directly impact electricity demand as the need for air conditioning grows within urban microclimates, increasing as much as 13.5% (Santamouris et al. 2015). Rising out- door temperatures and extensive growth in urbaniza- tion require suitable adaptation measures for sustainable urban development (Rizwan et al. 2008; Gromke et al. 2015). Adaptation measures include street vegetation (Toparlar et al. 2018; Morakinyo et al. 2020), water bodies (Yang et al. 2020; Zeeshan and Ali 2022a), urban geometry (Jamei et al. 2016), surface materials (Santamouris and Yun 2020; Zee- shan and Ali 2022b), and the reduction of anthropo- genic heat sources (Rizwan et al. 2008). INTRODUCTION During the last century, persistent global warming and increased urbanization have intensified ambient temperatures of urban areas by as much as 4 °K due to the proliferation of impervious surfaces. Extensive growth in urbanization and climate change have severely worsened the thermal environment of urban areas (Lai et al. 2019; Morakinyo et al. 2020). Urban areas are generally degraded by air pollution, surface materials, inadequate green infrastructure, and venti- lation (Akbari et al. 2016), all of which trap long- wave solar radiation inside urban streets and prevent the dispersion of absorbed energy during the day- time, thus affecting the surface energy balance of local urban microclimates. As a result, urban areas experience larger ambient air temperatures than their rural surroundings, giving rise to the urban heat Green Infrastructure with Actual Canopy Parameterization: A Simulation Study for Heat Stress Mitigation in a Hot-Humid Urban Environment By Muhammad Zeeshan, Zaib Ali, and Qasim A. Ranjha Abstract. Background: The urban heat island (UHI) phenomenon, resulting from rapid urbanization and aggravated by persistent climate change, is intensifying heat stress and temperature anomalies inside the urban microclimate, requiring the implementation of suitable adapta- tion measures for sustainable development. The integration of street trees inside the urban landscape is a strategy to alleviate the thermal stress of pedestrians. However, trees have variable potential for the regulation of thermal comfort depending on their different canopy shapes/drag. Therefore, a holistic understanding of tree plantings and species with respect to a particular climate is necessary for urban sustainability. Meth- ods: In this study, computational fluid dynamics (CFD) that employ unsteady Reynolds-averaged Navier-Stokes (URANS) equations were per- formed using FLUENT solver to analyze the cooling potential of isolated tree species based on 5 morphological characteristics and canopy shapes (i.e., tree height, trunk height, crown width, crown height, and leaf area density) in an urban area. Results: Results revealed a variable temperature regulation (i.e., 0.6 to 1.2 °K) depending on the tree species. Overall, the cooling effect was only observed in the vicinity of the tree canopy. This was due to the availability of shading and increased moisture content provided by the canopy foliage, which blocked shortwave radiation from the sun, as compared to its surroundings. Conclusions: The study findings show that leaf area density is the morphological trait that has the greatest impact on thermal comfort, as it results in low ambient air temperature irrespective of the type of urban density. Additionally, the most effective way to reduce thermal stress is to implement taller trees with uniform foliage density, which will produce a well-ventilated environment. Keywords. CFD; Sub-Configuration Validation; Thermal Stress; Tree Morphological Characteristics; Urban Microclimate. Scientific Journal of the International Society of Arboriculture
September 2023
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