Urban green effects on land surface temperature caused by surface characteristics: A case study of summer Beijing metropolitan region

The pace of urbanization in China has increased in recent decades. Accordingly, the urbanized area has expanded at a spectacular rate and the urban heat island (UHI) has intensified. Understanding the effects of the landscape pattern on the UHI is crucial for optimizing urban structure, which could mitigate the UHI. This study focused on green cover in an urban area. To investigate how the composition and configuration of urban green patches would affect their temperature in Beijing metropolitan region, China, especially the influence of the configuration of green patches on their cooling effect, the relationships between green surface temperature (GST), normalized difference vegetation index (NDVI), and normalized compactness index (NCI) were investigated by regression analyses, and a method to quantify the cooling effect of greens derived from the urban cool island and green space cool island was proposed. The image from the Landsat Thermal Infrared Sensor was used to estimate GST, and three images from the GF-2 Panchromatic & Multispectral Camera were used to obtain NDVI and calculate NCI. Our results showed that both NDVI and NCI had negative relationships to GST in summer, but only NCI strongly influenced the spatial cooling effect of greens. The further exploration of the influence of NCI on the cooling effect showed the NCI was negatively correlated to the cooling effect, which indicated that, for a given area, more compact green patches reduce the extent of the cooling effect.