Optimization of Microclimate Conditions Considering Urban Morphology and Trees Using ENVI-Met: A Case Study of Cairo City

Abstract

This research aims to optimize the use of trees to enhance microclimate conditions, which has become necessary because of climate change and its impacts, especially for cities suffering from extreme heat stress, such as Cairo. It considers elements of urban morphology, such as the aspect ratio and orientation of canyons, which play an important role in changing microclimate conditions. It also considers both sides of each canyon because the urban shading is based on the orientation and the aspect ratio, which can provide good shade on one side of the canyon but leave the other side exposed to direct and indirect radiation, to ensure a complete assessment of how the use of trees can be optimized. As Cairo city is very large and has a variety of urban morphologies, a total of 144 theoretical cases have been tested for Cairo city using ENVI-met to cover the majority of the urban cases within the city (Stage 1). Then, the same tree scenarios used in the theoretical study are applied to an existing urban area in downtown Cairo with many urban morphology varieties to validate the results of the theoretical study (Stage 2). After testing all cases in both stages, it became very clear that the addition of trees cannot be the same for the different aspect ratios, orientations, and sides of the different canyons. For example, eastern roads should have more trees than other orientations for all aspect ratios, but the required number of trees is greater for the northern side than the southern side, as the southern side is partially shaded for a few hours of the day by buildings in moderate and deep canyons. Northern streets require a very limited number of trees, even in shallow canyons, on both sides. The correlation between the number of trees on each side for the different orientations and aspect ratios shows a strong negative relationship, but the correlation values change between the different sides and orientations. The results of applying trees to an existing urban area show almost the same results as the theoretical study’s results, with very slight differences occurring because of the irregularity of the existing study area. This proves that when adding trees, not only the aspect ratio and orientation but also the side of each canyon should be considered to ensure that pedestrians, in all cases, have better microclimate conditions and that the use of trees is optimized.