Developing a comprehensive strategy to optimize tree use for mitigating heat stress.
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Date
2025
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Considering urban morphology and limited resources through dynamic and static thermal comfort analysis. A case study of Cairo city.
Abstract
This cumulative dissertation aims to develop a comprehensive and efficient strategy to enhance urban microclimate conditions in cities experiencing heat stress and intense solar radiation, with a focus on the metropolitan area of Greater Cairo. This study is conducted in three main stages, each addressing different aspects of urban microclimate management and optimization through the strategic use of trees. Stage 1 involves developing an efficient urban tree strategy (UTS) aimed at balancing an enhancement of microclimate conditions with the city’s water scarcity. This stage implements three strategic components: (1) selecting suitable tree species, (2) utilizing innovative irrigation technologies, and (3) determining the optimal number and arrangement of trees. When applying the strategy’s there are average physiological equivalent temperature (PET) reductions of -5.18˚ and -6.36˚ at 16:00 and 17:00, respectively. Additionally, through the implementation of irrigation technologies that are part of the UTS, water demand is reduced to only 15% when trees with larger canopies are used. Stage 2 focuses on optimizing the use of trees to enhance microclimate conditions by considering elements of urban morphology, such as the aspect ratio, orientation of canyons, and the canyon side. In this stage, a total of 144 theoretical cases are simulated using ENVI-met to represent the majority of urban conditions within the city (Step 1). Following this, the same tree scenarios used in the theoretical study are applied to an existing urban area in downtown Cairo, to validate the results of the theoretical study (Step 2). Findings demonstrate that for optimal pedestrian microclimate conditions and tree use, it is important to consider not only the aspect ratio and orientation of canyons but also which side of the canyon trees are planted. Stage 3 analyzes and assesses the impact of different urban forms and tree densities on the dynamic physiological equivalent temperature (DPET) experienced by pedestrians walking further than the average walking distance (750 m), using ENVI-met. The results prove that the DPET exhibits different values from the steady physiological equivalent temperature (SPET) at each point along the walking routes. However, the DPET is closely related to changes in the SPET. On the one hand, prolonged periods of lower or higher SPET result in reductions or increases in the DPET. On the other hand, frequent fluctuations in the SPET stabilize the DPET. Overall, this research provides a scientifically validated framework for optimizing urban greenery to mitigate extreme heat while conserving water. The findings are pivotal for developing sustainable, climate-resilient urban environments.
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Keywords
Urban heat island (UHI), Outdoor thermal comfort, Urban trees, Urban shading, Dynamic thermal comfort, Static/steady thermal comfort, ENVI-met greenery simulation, Urban cooling stratergies
Subjects based on RSWK
Stadtplanung, Stadtklima, Stadtgrün, Begrünung, Hitze, Wasserbedarf