Impact of Urban Vegetation on Outdoor Thermal Comfort: Comparison between a Mediterranean City (Lecce, Italy) and a Northern European City (Lahti, Finland)

Elisa Gatto,Fabio Ippolito,Eeva Aarrevaara,Jose Luis Santiago,Leonardo Perronace,Rohinton Emmanuel,Riccardo Buccolieri

doi:10.3390/f11020228

Abstract

This paper is devoted to the application of the modelling approach, as one of the methods for the evaluation of thermal comfort, to neighborhoods located in two cities characterized by a different climate, i.e., a Mediterranean city in southern Italy (Lecce) and a northern European city in southern Finland (Lahti). The impact of the presence of vegetation in both places is evaluated and compared, further considering alternative scenarios for thermal comfort improvement. The thermal comfort condition is expressed in terms of indices (mean radiant temperature (MRT) and predicted mean vote (PMV)). Results show that at pedestrian level the presence of vegetation lead to an improvement of thermal comfort in summer of about 2 points in both neighborhoods. This improvement is also evident observing the spatial distribution of MRT with a difference of 7 °C in the Lecce neighborhood and 3 °C in Lahti. In winter, thermal discomfort is observed in the presence of vegetation with a difference of 1.3 °C in the Lecce neighborhood and 1.5 °C in Lahti in terms of MRT. However, trees and green cover have the important potential to offset climate change impact and to make urban environments less thermally stressful. This study aims to guide urban planners towards a motivated and necessary transaction towards new green infrastructure whose effect should, however, be analyzed and investigated case by case.

Highlights

In the face of rapid changes to global climate [1] as well as increasing urbanization [2], the role of cities in both mitigating the changes to climate as well as adapting to cope with the negative consequences of such changes is receiving great attention [3]
The time evolution for the new scenario does not change at P2 and P3, while it changes at P1 where the maximum increase with respect to the no vegetation case is 0.2 ◦ C
In Aleksanterinkatu, Tair of current scenario is about 1 ◦ C higher during the entire period at P1 and P2, while in the new scenario at P1 the time evolution is similar to that without vegetation and at P2 there is a maximum increase of 0.7 ◦ C at 11.00 that tends to decrease during the evening

Summary

Introduction

In the face of rapid changes to global climate [1] as well as increasing urbanization [2], the role of cities in both mitigating the changes to climate as well as adapting to cope with the negative consequences of such changes is receiving great attention [3]. Given the superimposing effect of microclimate variations due to urbanization (the so-called urban heat island effect [4]), the importance of making urban space attractive and accessible has the double benefit of climate change mitigation as well as social, cultural and economic benefits [5]. There are several ways comfort, usability and attractiveness of outdoor spaces could be enhanced. The key principle is to integrate local climate with urban form and the fabric of the building [7]. These could be achieved by the manipulation of settlement geometry, street orientation and external factors [8] as well as climatically linking the inside of buildings with the outside [9]. Perhaps the greatest benefit to outdoor comfort is achieved by the introduction of green infrastructure (e.g., [10,11,12,13,14])

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