Role of Built Geometry in the Micro-climatic Modifications: Case of Addis Ababa, Ethiopia

Abstract

[EN] The urban expansion in the city has created a negative impact on the outdoor microclimate. With the lack of green spaces in the city, the built mass itself can be designed in such a way that it can have a minimal negative impact on the adjacent outdoor spaces. This study analyzed the microclimatic behavior of outdoor open spaces in the existing built environment and attempted to identify the favorable configuration of the built environment with an emphasis on the extreme temperature of summer days. In this study, the existing site is compared with the modified built environments. The modifications were done in terms of building orientations and building heights. The numerical model `Envi-MET 5.0.2¿ was used to simulate the modified built mass. Meteorological data was used as input for various calculations. Microclimatic indexes Ambient temperature (Ta), wind speed (Va), and mean radiant temperature (Tmrt) were evaluated and a comparative analysis is done. To calculate Tmrt, `Rayman Pro¿ was used. Results have shown a strong correlation between the geometric parameters of the built environment and the microclimatic indices. It was also seen that the slight modification in the built mass resulted in different values of microclimatic indices. The study also highlights the importance of shading to improve the microclimate. The sky view factor (SVF), height-to-width (H/W) ratio, the orientation of the building surfaces, and the relation of vertical surfaces to each other are important aspects to consider for the future design of outdoor spaces. This study is important for the sustainability of the urbanized space in a way it helps to improve the microclimate of the open spaces and ultimately helps mitigate the urban heat island effect of the city by only adopting the right approach to the design of the built masses.