Assessing the Distribution of Urban Green Spaces and its Anisotropic Cooling Distance on Urban Heat Island Pattern in Baotou, China

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.

Study of the Cooling Effects of Urban Green Space in Harbin in Terms of Reducing the Heat Island Effect

“…Increasing the NDVI by 0.1 would lead to a decrease of surface temperature of 1.82 • C (2007), 0.51 • C (2011) and 1.82 • C (2015). Li et al reported a correlation between NDVI and the UHI effect in the city of Baotou, which has similar latitude to Harbin, during the growing season (July-August) [12]. We obtained a similar conclusion, namely that NDVI had a negative relationship with the UHI effect during summer.…”

“…Green space composition refers to the variety of land cover types (i.e., size, density and evenness of urban green space patches), and configuration is related to the spatial arrangement and layout (i.e., shape, aggregation and cohesion of patches) [8,9]. The size of urban green space has a strong influence on its cooling effect [10][11][12]. Green spaces of average-size (50 ha) can lower the temperature range 1.5-3.0 • C [13,14], while the larger ones (>150 ha) have a more substantial cooling effect on the surrounding temperature [7].…”

Seasonal Variations of the Urban Thermal Environment Effect in a Tropical Coastal City

“…Urban heat island intensity (UHII) is an important indicator to evaluate the severity of SUHI [65]. In this study, UHII is defined as the difference between the LST of each pixel and the mean surface temperature in HJ-1B images [66]. The approach tends to differ from the other regional or global UHII analyses that took "rural" area (a certain distance away from urban) as reference locations [67,68], since Shenzhen is the first city in China with no rural administrative system.…”

Is Colombo city, Sri Lanka secured for urban green space standards?

“…They provide key ecological functions such as carbon storage, soil conservation, noise buffering, maintenance of air quality, reduction of air temperature etc. to protect and maintain bio diversity of the city (Bao et al, 2016). They contribute in a positive manner to maintain public health by facilitating appropriate space for physical exercise to improve physical and psychological well-being (Cohen et al, 2007;Zhao et al, 2013).…”

“…According to that, a space of 0.41km 2 has to be kept as urban parks for 1000 residents (Nicholls, 2001). The Six Acre Standard of National Playing Fields Association of United Kingdom is another standard which recommends 0.24km 2 as the open space for 1000 residents (Nicholls, 2001).…”