Quantitative analysis of urban cold island effects on the evolution of green spaces in a coastal city: a case study of Fuzhou, China

Urbanization is accompanied by drastic changes in the distribution of urban green space (UGS). This study aimed to analyze the relationship between the land surface temperature difference (∆LST) and the evolution of UGSs in the main area of Fuzhou City from 1993 to 2013 using a set of remote sensing images. The results manifest that with the maximum area of UGS loss, the less UGS extension, and the less UGS exchange, the UGS area declined sharply, which results in the rise of urban thermal problem and demonstrates the negative relationship between the UGS area and its internal land surface temperature (LST). Different UGS evolution types produced a diversified temperature response pattern. According to the profile assessment, a ∆LST above 10 °C, caused by the UGS loss converted to construction land, occurred in the peak position of the online profiles. Among the UGS loss, the conversion of water had the most apparent ∆LST, followed by wetlands and forest/grass areas. The threshold value of the UGS loss area (TVoA) was quantified by analyzing the temperature change effects based on the UGS evolution temperature effect index (GETX). We concluded that the urban heat island (UHI) can be effectively alleviated by keeping the magnitude of the UGS extensions equal to the UGS loss and the UGS utilization area below 0.04 km2 in Fuzhou City. Further analysis clarified that vegetation cover changes and the evolution of UGSs were the main factors controlling the distribution of the cold/heat island.