Abstract
Urban planning must consider the outdoor thermal comfort of city dwellers, particularly in cities where climate and the effects of climate change may severely influence human health and wellbeing in increasingly hot summers. The role of the urban forest in ameliorating this problem is decisive. The present study is based on a campaign of meteorological measurements in a large number of sites using a mobile data collection system to allow a human-centred approach. The aim is to quantify the different microclimates and thermal comfort conditions in six classes of urban morphology, discriminating landtypes with or without trees. In the case study of Florence, local physical characteristics of the sites; Sky View Factor (SVF), tree shade, ground surface cover, and canyon effect, can moderate human exposure to potentially uncomfortable thermal conditions during a typical Mediterranean summer. Significant differences in Universal Thermal Comfort Index (UTCI) were observed between treeless piazzas and streets and landtypes with trees or high height to width ratio (narrow alleys). Varying levels of SVF and tree cover in the sites allowed the construction of multivariate models, which revealed that, during common summer afternoon conditions, decreases of SVF by 12.5% or increases of tree cover by 25% can reduce the UTCI by 1°. Additionally, the total site factor, by incorporating temporally integrated sun exposure with the sky view factor, revealed itself a promising variable for future studies to use.
Highlights
It is widely recognised that sustainable urban planning and development must take the outdoor thermal comfort of city dwellers into consideration [1]
Extreme air temperature in heatwave events may become exacerbated due to the Urban Heat Island (UHI) effect whereby the energy balance of cities is modified by factors such as the thermal properties of building materials [5], a reduction in the spatial coverage of green areas which provide evapotranspirative cooling [6], and the arrangement of buildings in urban canyons [7,8]
The liveability and vitality of cities can be greatly improved by a careful consideration of the factors which influence outdoor thermal comfort resulting in physical, social, economic, and environmental benefits [15]. These benefits can be incorporated into urban planning and design options which aim to ameliorate the UHI problem and reduce climate change related risks [16]
Summary
It is widely recognised that sustainable urban planning and development must take the outdoor thermal comfort of city dwellers into consideration [1]. Extreme air temperature in heatwave events may become exacerbated due to the Urban Heat Island (UHI) effect whereby the energy balance of cities is modified by factors such as the thermal properties of building materials [5], a reduction in the spatial coverage of green areas which provide evapotranspirative cooling [6], and the arrangement of buildings in urban canyons [7,8]. The liveability and vitality of cities can be greatly improved by a careful consideration of the factors which influence outdoor thermal comfort resulting in physical, social, economic, and environmental benefits [15] These benefits can be incorporated into urban planning and design options which aim to ameliorate the UHI problem and reduce climate change related risks [16]
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