Abstract
Urban forests can be an effective contributor to mitigate the urban heat island (UHI) effect. Understanding the factors that influence the cooling intensity of forest vegetation is essential for creating a more effective urban greenspace network to better counteract the urban warming. The aim of this study was to quantify the effects of spatial patterns of forest vegetation on urban cooling, in the Shanghai metropolitan area of China, using correlation analyses and regression models. Cooling intensity values were calculated based on the land surface temperature (LST) derived from remote sensing imagery and spatial patterns of forest vegetation were quantified by eight landscape metrics, using standard and moving-window approaches. The results suggested that 90 m × 90 m was the optimal spatial scale for studying the cooling effect of forest vegetation in Shanghai’s urban area. It also indicated that woodland performed better than grassland in urban cooling and the size, shape, and spatial distribution of woodland patches had significant impacts on the urban thermal environment. Specifically, the increase of size and the degree of compactness of the patch shape can effectively reduce the LST within the woodland. Areas with a higher percentage of vegetation coverage experienced a greater cooling effect. Moreover, when given a fixed amount of vegetation covers, aggregated distribution provided a stronger cooling effect than fragmented distribution and increasing overall shape complexity of woodlands can enhance the cooling effect on surrounding urban areas. This study provides insights for urban planners and landscape designers to create forest adaptive planning strategies to effectively alleviate the UHI effect.
Highlights
Urbanization has taken place at an unprecedented rate around the world in the past few decades.More than half of the world’s population lives in towns and cities and the population will swell to about 5 billion by 2030 [1]
The percentages of landscape (PLAND) of woodland were calculated by the moving-window method and showed significant linear relationships with temperature differences under four tested method and showed significant linear relationships with temperature differences under four tested window sizes/spatial sizes/spatial extents extents (Figure (Figure 3)
The results indicated that the effect of SI on the cooling intensity were statistically significant for PA_01 (R 2 = 0.54, p < 0.01), PA_05 (R2 = 0.72, p < 0.01), PA_10 (R 2 = 0.63, p < 0.01), and PA_15 (R 2 = 0.53, In order to better understand the effect of shape of woodland patches on cooling intensity by different sizes, this study classified the woodland patches into several patch area (PA) classes including the following: PA_01 (0.9–1.1 ha), PA_05 (4.9–5.1 ha), PA_10 (9–11 ha) and PA_15 (13–17 ha)
Summary
More than half of the world’s population lives in towns and cities and the population will swell to about 5 billion by 2030 [1]. Much of this urbanization will take place in Africa and Asia, bringing huge social, economic, and environmental changes [2]. One of the noticeable impacts of rapid urbanization on the environment is the urban heat island (UHI) effect [3], which is a phenomenon that urban areas have higher temperatures compared to the surrounding rural areas [4,5,6]. Increased temperatures due to the UHI effect leads to reduced thermal comfort for urban dwellers and increased energy consumption for cooling urban indoor environments [7]. UHI mitigation is urgent in order to improve the urban living environment [10]
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