Urban expansion in Shenzhen since 1970s: A retrospect of change from a village to a megacity from the space

Quantifying the characteristic of urban expansion is the prerequisite of understanding its social and ecological outcomes. Here, using Shenzhen, a city that grew from a fishery village to a megacity in 40 years as a case study, we quantified the urban expansion at two scales, over the entire city and within the city, at district level. Twelve land cover maps from 1979 to 2017 were classified using Landsat TM/ETM+/OLI images. Based on the long-term map series, we examined the impacts of urban expansion on land cover change, and the directional variations of those change trajectories. Our results demonstrated that: (1) Shenzhen experienced rapid and dramatic urban expansion from 1979 to 2017. The developed land increased by 3400%, from 27 km(2) to 946 km(2) with an average annual growth of 24 km(2). While the developed land continued to increase, its expansion rate exhibited a general decreasing trend, except for the time period of 1990-1995. (2) The urban expansion primarily consumed forest, water, and farmland. Forest experienced a 44% loss from 1979 to 2017, equals 659 km(2) of land. (3) The urban expansion exhibited distinctive directional variations from the southwest to the northeast, following a fan model. The within city differences are potentially related to changes of regional geographical conditions. In the western coastal area, water experienced major changes, and in the northern region forest had the most lost. The understanding of urban expansion variations within the city will help local government in designing and implementing effective plans that balancing future urban development and ecological conservation.