The Expansion and Gradient Evolution of Impervious Surface within the Guangdong-Hong Kong-Macao Greater Bay Area from 1987 to 2017

The impervious surface is considered an important feature to measure the urbanization and its spatial expansion. In the current study, the spatial-temporal expansion characteristics and evolution trends of the impervious surface are explored using gravity center, standard deviation ellipse, and gradient analysis in Guangdong-Hong Kong-Macao (GHM) Greater Bay Area during 1987-2017. The results show that: (1) The impervious surface areas of GHM Greater Bay Area has increased from 1839.34 km2 to 12 385.93 km2 in the past 30 years, with an annual growth area of 351.55 km2. In the 21st century, the urbanization process accelerated, and and each city exhibited different expansion characteristics. Moreover, it formed a spatial expansion pattern driven by core cities such as Guangzhou, Shenzhen, Hong Kong, and Macao, resulting in the formation of various secondary cities, and the development of network structures; (2) Urban construction and expansion are close to the coastal area. The gravity center of the impervious surface of the GHM Greater Bay Area is located near the junction of Panyu, Guangzhou, and Shunde, Foshan. However, the gravity center and urban development trends are from west to the east bank of the Pearl River, and toward Guangzhou, Dongguan, and Foshan. The urban development of Guangzhou, Dongguan, and Foshan promoted the change of gravity center of impervious surface; (3) The urban development of the GHM Greater Bay Area has apparent features of the expansion along the Pearl River and the coastline. Urban construction along both sides of the Pearl River tributary has always occupied a central position. Early urban construction was concentrated in the 70 km area on both sides, and the intensity of urban expansion increased sharply in the 21st century. The area within 50 km of the coastline is an urban high-intensity construction area. The expansion of the core urban and bay area in various places constitutes the development core of the GHM Greater Bay Area. Moreover, the urban construction has formed a coordinated development trend that is dominated by the main urban area and supplemented by the coastline. Furthermore, Although the construction of the GHM Greater Bay Area has become China's national strategy, but there exist problems due to the weak connections between cities. It is necessary to strengthen the interaction of elements in various cities, and make full use of the leading advantages of the core urban area to develop coastal industries, so as to realize the integration of urban and rural areas and economic development in the GHM Greater Bay Area. © 2021, Science Press. All right reserved.