Abstract
Increasing trends of urbanization lead to vegetation degradation in big cities and affect the urban thermal environment. This study investigated (1) the cooling effect of urban green space spatial patterns on Land Surface Temperature (LST); (2) how the surrounding environment influences the green space cool islands (GCI), and vice versa. The study was conducted in two Asian capitals: Beijing, China and Islamabad, Pakistan by utilizing Gaofen-1 (GF-1) and Landsat-8 satellite imagery. Pearson’s correlation and normalized mutual information (NMI) were applied to investigate the relationship between green space characteristics and LST. Landscape metrics of green spaces including Percentage of Landscape (PLAND), Patch Density (PD), Edge Density (ED), and Landscape Shape Index (LSI) were selected to calculate the spatial patterns of green spaces, whereas GCI indicators were defined by Green Space Range (GR), Temperature Difference (TD), and Temperature Gradient (TG). The results indicate that both vegetation composition and configuration influence LST distributions; however, vegetation composition appeared to have a slightly greater effect. The cooling effect can be produced more effectively by increasing green space percentage, planting trees in large patches with equal distribution, and avoiding complex-shaped green spaces. The GCI principle indicates that LST can be decreased by increasing the green space area, increasing the water body fraction, or by decreasing the fraction of impervious surfaces. GCI can also be strengthened by decreasing the fraction of impervious surfaces and increasing the fraction of water body or vegetation in the surrounding environment. The cooling effect of vegetation and water could be explained based on their thermal properties. Beijing has already enacted the green-wedge initiative to increase the vegetation canopy. While designing the future urban layout of Islamabad, the construction of artificial lakes within the urban green spaces would also be beneficial, as is the case with Beijing.
Highlights
Consequent to the critical process of rapid urbanization, the contemporary structure and function of cities have been changing [1,2], through expansion of urban periphery, modification of ecological diversity, and energy flows [3,4,5]
The main purpose of the study is to determine the degree of relationship or association between Land Surface Temperature (LST) and green space characteristics; scatter plots were drawn only to investigate whether any relationship between LST landscape metrics exists or not, and Pearson’s coefficient (r) was calculated to measure the degree of relationship or association between green space spatial patterns and LST
The results indicate that the LST of green spaces can be mitigated by reducing the impervious surfaces or by increasing the percentage of water body and vegetation
Summary
Consequent to the critical process of rapid urbanization, the contemporary structure and function of cities have been changing [1,2], through expansion of urban periphery, modification of ecological diversity, and energy flows [3,4,5]. Urban expansion or urban sprawl primarily depends on socio-economic factors, migration from rural to urban areas, urban planning, and land use policies. Lack of landscape policies and inappropriate urban planning are rapidly increasing city sizes in developing countries. The phenomenon of higher urban surface temperature is technically referred to as surface urban heat islands (SUHIs) [9,10]. This phenomenon is generally observed in cities, and its intensity depends on several factors including size, population, location, socio-economic activities, urban planning, and land use policies of the area under consideration [7,10,11,12,13,14]
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