How to Measure the Urban Park Cooling Island? A Perspective of Absolute and Relative Indicators Using Remote Sensing and Buffer Analysis

Abstract

Urban parks have been proven to cool the surrounding environment, and can thus mitigate the urban heat island to an extent by forming a park cooling island. However, a comprehensive understanding of the mechanism of park cooling islands is still required. Therefore, we studied 32 urban parks in Jinan, China and proposed absolute and relative indicators to depict the detailed features of the park cooling island. High-spatial-resolution GF-2 images were used to obtain the land cover of parks, and Landsat 8 TIR images were used to examine the thermal environment by applying buffer analysis. Linear statistical models were developed to explore the relationships between park characteristics and the park cooling island. The results showed that the average land surface temperature (LST) of urban parks was approximately 3.6 °C lower than that of the study area, with the largest temperature difference of 7.84 °C occurring during summer daytime, while the average park cooling area was approximately 120.68 ha. The park cooling island could be classified into four categories—regular, declined, increased, and others—based on the changing features of the surrounding LSTs. Park area (PA), park perimeter (PP), water area proportion (WAP), and park shape index (PSI) were significantly negatively correlated with the park LST. We also found that WAP, PP, and greenness (characterized by the normalized difference vegetation index (NDVI)) were three important factors that determined the park cooling island. However, the relationship between PA and the park cooling island was complex, as the results indicated that only parks larger than a threshold size (20 ha in our study) would provide a larger cooling effect with the increase in park size. In this case, increasing the NDVI of the parks by planting more vegetation would be a more sustainable and effective solution to form a stronger park cooling island.

Dominance of Influencing Factors on Cooling Effect of Urban Parks in Different Climatic Regions

“…However, the size of the buffer zone may affect the quantification of the PCE. Previous studies have used different sizes of buffer zone, such as 300, 500, 900, 990, and 1200 m, which were usually divided into approximately a 10~40 buffer ring with a width of 30 m to form the temperature curve [ 19 , 20 , 22 , 26 , 57 ]. Further, certain studies have used buffer widths based on the length of the park radius [ 58 ].…”

“…Second, the influencing factors of the PCE were not fully considered. For example, there are a few impervious surfaces within parks, such as roads and rest places; however, it was difficult to identify them in this study [ 21 , 26 ]. Further, humidity, wind speed, etc., may also affect the PCE [ 26 , 61 ]; however, these factors were not considered in this study.…”

“…For example, there are a few impervious surfaces within parks, such as roads and rest places; however, it was difficult to identify them in this study [ 21 , 26 ]. Further, humidity, wind speed, etc., may also affect the PCE [ 26 , 61 ]; however, these factors were not considered in this study. Third, this study only focused on the cooling effect of urban parks during the daytime in summer.…”

“…These conclusions were derived from previous studies on the PCE in the case of individual cities; however, the national spatial pattern of the PCE remains unclear [ 25 ]. In addition, case studies on the PCE have been conducted only considering individual cities, where the number and types of urban parks may be limited [ 20 , 26 , 27 ]. Therefore, the PCE must be investigated on a larger spatial scale as large sample studies may provide more general conclusions, which may better support urban park planning towards the mitigation of the UHI.…”

Exploring the cooling effect of urban parks based on the ECOSTRESS land surface temperature

“…It's important to note that the characteristics of different vegetation (e.g., tree and bush) and water have a huge difference (e.g., heat capacity and reflectivity) Kong et al, 2021;Yang et al, 2020Yang et al, , 2021c. It is necessary to consider the types of parks in the research of the CE (Zhu et al, 2021). LCZ derived from logical division of the landscape (Stewart, 2011), can be used to overcome the limitations of the "urbanrural" dichotomy and to further investigate the impacts of park forms on the CE at local scales (Stewart and Oke, 2012;Yang et al, 2019;Wu et al, 2020).…”