The vegetation for mitigating the microclimate and designing livable and healthy public spaces in Palermo City Centre

Abstract

Urban morphology and increasing building density play a key role in the overall heat and energy balance of our cities. The urban environment and CO2 emissions resulting from human activities cause a local increase of temperature, a phenomenon known as Urban Heat Island (UHI). This is also due to the reduction of vegetation in urban areas. The benefits that green spaces have in urban planning have been widely acknowledged. In particular, in temperate and hot contexts, plants help to reduce the extreme summer temperatures, improving people’s outdoor and indoor thermal comfort and, at the same time, reducing the buildings’ energy demand for cooling. The way plants affect urban climates is generally associated to two different direct and indirect effects. The firsts refer essentially to the shading and lowering wind speed and the seconds to the evapotranspiration. In temperate and hot contexts, lower air temperatures are essential both to improve thermal comfort conditions of pedestrians and building occupants and to limit energy use for cooling. Besides the environmental benefits, several studies have shown how urban greening can also affect human well-being and social behaviour. Recent researches have demonstrated that responses to the presence of trees and other vegetation can be linked directly to health, and in turn related to economic benefits of visual quality documenting social benefits of living, working, or playing in a green environment. Despite the advantages provided, trees are still often considered as a costly strategy. Therefore a quantitative evaluation of the microclimatic effects of vegetation could play a role in informing the green planning in order to maximize its effect. This paper shows the results of a research carried out at the Department of Architecture of the Polytechnic School of Palermo University, with the aim to quantitatively evaluate the microclimate effects due to the increase of vegetation in urban areas located in the historical city centre of Palermo and in the surrounding areas in which SH complexes have been built after the II World War. The purpose is to demonstrate the significant influence that vegetation can have even in densely urbanized areas with few available spaces for the integration of plants, as in the case of historical centres of Mediterranean cities.