Mitigating Effect of Urban Green Spaces on Surface Urban Heat Island during Summer Period on an Example of a Medium Size Town of Zvolen, Slovakia

Abstract

Climate change affects the urban population’s health and quality of life. Urban green spaces (UGS) underpin several essential ecosystem services, amongst them climate regulation. Urban vegetation mitigates high temperatures and, thus, reduces the heat stress for urban residents. The study aimed to verify whether the Surface Urban Heat Island (SUHI) effect manifests itself even in a medium size town (Zvolen, Slovakia) surrounded by agricultural and forested landscape and to quantify the temperature mitigating effect of urban green spaces. Land surface temperature (LST) and SUHI distribution were derived from the Landsat data during the summer months of 2010–2021. To statistically prove the cooling effect of the urban vegetation, we tested (by one-way ANOVA) LST within three urban zones of the Zvolen municipality defined by the Copernicus imperviousness density data: (a) dense urban area (31–100% impervious surfaces), (b) discontinuous urban area (1–30% impervious surfaces), (c) urban green spaces (0% impervious surfaces), and the open land surrounding the town (0% impervious surfaces). The results showed a statistical difference in temperatures between all urban areas (all zones) and the open land. Moreover, the UGS temperature was statistically different compared to the other urban zones. The mean temperature difference through the years 2010–2021 between urban green spaces and the dense urban area was 3.5 °C, with a maximum of 4.9 °C and a minimum 1.7 °C in favor of the urban spaces. Moreover, the temperature of urban green spaces and open land varied during the studied summer period. The warmer the weather, the higher the difference, while at the end of August, on a notably colder day, there was no significant difference between them. The results confirmed that UGS are significantly cooler during hot days, and they can mitigate the local climate.

Quantification of the Cooling Effect and Cooling Distance of Urban Green Spaces Based on Their Vegetation Structure and Size as a Basis for Management Tools for Mitigating Urban Climate

“…In our previous paper [48], we confirmed the existence of an urban heat island even within a medium city with a large proportion of forest in its vicinity, as well as a cool island effect of urban green spaces within the city. However, we did not investigate the difference between the structure and size of each urban green space's area nor the spatial extent of their influence as crucial parameters for the effective management of the urban climate.…”

“…The most significant cooling effect is provided by large (over 1 ha) green spaces with trees (GTl), where the cooling intensity (difference of LST compared to an urban area without vegetation) was almost 4.5 • C on average (maximum almost 6 • C) and the cooling distance was significant up to 90 m (less significant up to 180 m). As mentioned above, GGl and GTm have similar effects, with a higher cooling intensity (2.9 • C versus 2.5 • C on average) for GGl; however, the cooling effect (cooling distance) extends to a greater distance (up to 90 m) for GTm compared to GGl, where the cooling effect only extends to 30-60 m. Small areas with trees (GTs) and medium and small areas without trees (GGm and GGs) have an average cooling intensity below 2 • C; for GGm and GGl, this is even below 1.7 • C. This is the threshold below which the differences should already be evaluated with some caution due to the accuracy of LST determination using the Single-Channel Algorithm from Landsat imagery [48]. For GTs, their cooling effect on their surroundings was significant and extends to at least 60 m. For GGm and GGs, their cooling effect their surroundings was not demonstrated.…”

“…In this context, the accuracy of LST determination from Landsat imagery using a single-channel algorithm should also be considered. Based on several works [69,[71][72][73][74][75], we can assume that the degree of accuracy of our calculations (which will need to be verified by measurements in the future) is approximately 1.7 • C [48]. Hence, we can only assess the cooling effect with values up to 1.7 • C with some caution.…”

Progress in Research on Net-Zero-Carbon Cities: A Literature Review and Knowledge Framework

“…Meanwhile, the effectiveness of green spaces in mitigating the UHI effect can be improved by optimizing the size and shape of parks when designing and planning urban parks [107][108][109]. It has been shown that urban thermal environments can be improved through orderly planning of green infrastructure and management of long-term performance, which can mitigate the heat island effect [110][111][112] and slow down the rate of urban sprawl, leading to some reduction in temperature [113][114][115].…”

Quantifying Urban Spatial Morphology Indicators on the Green Areas Cooling Effect: The Case of Changsha, China, a Subtropical City

“…Thus, green city areas have significant advantages in reducing the UHI. Meanwhile, in the study of green city areas and UHI [32], the effective cooling distance of green city areas is a key indicator for evaluating the effectiveness of green city areas in mitigating the UHI [33,34]. Therefore, accurate estimation of the range of green city areas cooling is crucial.…”