Abstract
An essential part of urban natural systems, urban green spaces play a crucial role in mitigating the urban heat island effect (UHI). The UHI effect refers to the phenomenon where the temperature within a city is higher than that of the surrounding rural areas. The effects of the spatial composition and configuration of urban green spaces on urban land surface temperature (LST) have recently been documented. However, few studies have examined the effects of the directionality and distribution of green spaces on LST. In this study, we used a landscape index to describe the change in pattern of heat island intensity for the city of Baotou, China. We then used a semi-variable function and nearest neighbor algorithm to analyze the cooling effects of green spaces. We found that: (1) the cooling distance of an urban green space was not only influenced by its size, vegetation cover, and shape, but also showed anisotropy. In general, the larger the area of the urban green space and the higher the value of Normalized Difference Vegetation Index (NDVI; a measure of plant photosynthetic activity), the larger the cooling distance within a certain threshold. Green spaces with more regular shapes displayed higher LST mitigation; however, the cooling distance was directional, and cooling effects depended on the semi-major axis and semi-minor axis of the green space. (2) The distribution of the urban green space within the landscape played a key role in mitigating the UHI effect. Within a certain area, the cooling effect of green spaces that are evenly distributed was greater than that which was associated with either green spaces that were large in area or where greens spaces were aggregated in the landscape. Therefore, within urban areas, where space is limited, urban planning should account for green spaces that are relatively scattered and evenly distributed to maximize cooling effects. The results of this study have key implications for sustainable urban planning and development; to mitigate urban heat island effects it is important to not only increase canopy cover or the size of urban green spaces, but also to optimize their spatial configuration.
Highlights
Urban areas are becoming increasingly important and the United Nations projects that more than 65% of the global population will be urban dwellers by the year 2050 [1]
Spatiotemporal Variations of urban heat island (UHI) Intensity From the temperature retrieval and heat island intensity classification (Equation (5) and Table 1), we found that the heat island intensities of Baotou were mostly classified as moderate, strong, or very strong UHIs
These moderate to very strong UHIs were distributed in the downtown area, specISiPfiRcSaIlnlyt
Summary
Urban areas are becoming increasingly important and the United Nations projects that more than 65% of the global population will be urban dwellers by the year 2050 [1]. The urban heat island (UHI) effect refers to the phenomenon where the temperature within a city is higher than that of the surrounding rural areas [2,3,4]. The reduced natural surroundings, high exhaust heat emissions, increased impervious surface and surface roughness, and narrow urban skyline associated with cities often results in this increased temperature effect [5,6]. More research into the UHI effect and how to mitigate it [10,11] will be of great importance for effective improvement of the urban ecological environment and to improve the conditions of human settlements within cities [12]
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