Thermal Comfort Assessment in Urban Green Spaces: Contribution of Thermography to the Study of Thermal Variation between Tree Canopies and Air Temperature

Abstract

Understanding the thermal effects of different urban patterns that constitute today’s urban landscapes is critical to the development of urban resilience to climate change. This article aims to assess the efficiency of urban green spaces in thermal regulation. Through thermography, we explored the interaction between air temperature and the spatial components within these environments. Through comparative analysis involving a UAV, we studied the relationship between air temperatures at varying altitudes and the temperature within tree canopies. The results revealed significant differences in the thermal distribution between impervious urban areas with buildings and green spaces. These findings provide important information for assessing thermal comfort and the efficiency of urban green spaces in mitigating the impact of extreme heat events. During the summer months, green spaces, due to shade and the enhanced absorption of solar radiation by trees, exhibited lower temperatures compared to impervious areas. However, in winter, urban areas displayed higher temperatures, attributable to their heat retention capacity. This study contributes to the existing knowledge base by providing an in-depth examination of the thermal efficiency of urban green spaces across different layers of their lower atmosphere. Our results underscore the crucial role of tree cover in thermal comfort regulation, offering valuable information for sustainable urban planning. These insights are particularly relevant for the design of more comfortable and resilient environments in response to climatic variations and for the crafting of a tree-planting strategy in Mediterranean climate cities, an area where the impacts of climate change are becoming increasingly apparent.

Variation the in relationship between urban tree canopy and air temperature reduction under a range of daily weather conditions

“…Although spatial patterns of inter- and intra-urban surface temperature and inequity are well documented [ 19 , 20 ], less is known about spatio-temporal variability in air temperatures as they relate to urban land cover. The variable effects of tree canopy and impervious surface on air temperature throughout any relatively warm day, or across many days with varied cloud cover remains poorly understood [ 21 ].…”

The Thermal Regulator Role of Urban Green Spaces: The Case of Coimbra (Portugal)

“…Both approaches utilized identical thermal sensors (Tinytag Plus 2-TGP-4020, Chichester, West Sussex, UK), enhancing consistency and reliability. These methods have been tested and demonstrated [36,42,43] in a larger-scale study highlighting the importance of urban green spaces, especially tree canopies, in providing thermal comfort and mitigating the impacts of climate change. In previous research [36,42], temperature data from pedestrian paths were collected using calibrated data loggers (Tinytag Plus 2 − TGP-4020, Chichester,West Sussex, UK) positioned at a 1.5-m height, mirroring the temperature experienced by citizens.…”

“…These methods have been tested and demonstrated [36,42,43] in a larger-scale study highlighting the importance of urban green spaces, especially tree canopies, in providing thermal comfort and mitigating the impacts of climate change. In previous research [36,42], temperature data from pedestrian paths were collected using calibrated data loggers (Tinytag Plus 2 − TGP-4020, Chichester,West Sussex, UK) positioned at a 1.5-m height, mirroring the temperature experienced by citizens. Special attention was given to shielding the sensors from direct sunlight exposure in order to ensure accurate measurements.…”

“…Only after this could an average temperature value be determined-a methodology frequently adopted in aerial assessments. Utilizing the Empirical Bayesian Kriging tool in ArcGIS Pro, a georeferenced temperature map was crafted for each individual survey [36,41,43].…”

“…While this study predominantly concentrates on the capacity of urban green spaces to regulate and reduce surface air temperatures, it also delves into discerning the vertical thermal shifts across varied spatial configurations in these green areas. Additionally, the research probes the interplay between these lush urban environments and their neighboring built-up regions, areas where the phenomenon of the urban heat island effect is welldocumented [20,[35][36][37]. By identifying the distinct thermal mosaics within a green space, researchers and urban designers can strategize to optimize the spatial configurations that should be prioritized in green infrastructure planning for a sustainable city, with a specific focus on thermal regulation [34].…”