The Impact of the Small Urban Green Space on the Urban Thermal Environment: The Belgrade Case Study (Serbia)

Small green spaces are the most common type of greenery in cities, but very little is known about their impact on thermal comfort. It has been established that larger green spaces (large city parks, urban forests, etc.) have a significant effect on the formation of thermal comfort in cities. Conversely, it has been shown that this effect is highly variable in smaller green spaces (particularly those <3 ha). This study investigated the impact of smaller green spaces (<3 ha) of various categories (parks, squares, and street tree lines) on the thermal comfort of urban open spaces. In total, 18 green spaces in Belgrade were selected, where specialised meteorological measurements were conducted during summer and winter, and the PET index and UTCI were calculated using the RayMan Pro (Version 3.1 Beta) software. Research has shown that green spaces ranging from 0.9 to 3 ha have an average difference of 4.04 °C in the PET index and 3.27 °C in the UTCI. For areas between 0.3 and 0.9 ha, the differences are 2.32 °C for PET and 2.05 °C for UTCI, while for spaces <0.3 ha, the differences are 2.19 °C for PET and 2.12 °C for UTCI. In all cases, the values of the PET index and UTCI were higher in green spaces compared to areas without greenery, with differences ranging from 2.19 to 4.04 °C for PET and 2.05–3.27 °C for UTCI. It was determined that green spaces <3 ha increased the PET index by an average of 2.75 °C and the UTCI by 2.41 °C. The results of this study showed that despite their size, small green areas can significantly improve thermal comfort. This study highlights the importance of these green spaces and provides a basis for the planning of new or renovated existing urban green spaces to mitigate the effects of climate change in cities.