Spatiotemporal Variations and Driving Factors of Coastline in the Bohai Sea

The utilization and protection of coastlines play a crucial role in the sustainable development of coastal cities. The coastline designations in recent years have witnessed more coastal areas worldwide undergoing significant land reclamation for agriculture, industry, and urbanization purposes. This study used remote sensing images from 1986 to 2016 to analyze spatiotemporal changes in the coastlines of 13 cities around the Bohai Sea, which cover one city (Tianjin City) and three provinces (Liaoning, Hebei, and Shandong). Using coastline and socioeconomic data from 1986 to 2016, a partial least-squares regression (PLSR) model was established to analyze factors affecting the utilization of coastlines in each city. The results showed that from 1986 to 2016, the retention rates of natural coastlines in the cities around the Bohai Sea decreased, and the overall coastline expanded toward the sea. Furthermore, the impacts of human activities were prominent on the silty mud and sandy coastlines. Economic development, population growth, and urbanization were the main drivers of the development and construction of coastal cities, which changed the coastlines around the Bohai Sea to a state of high-intensity use. In addition, national macro policies and the external market environment indirectly drove the intensity of coastline use through regulations and interventions in cities. However, there were significant differences in the levels of development of the cities surrounding the Bohai Sea. In the future, the differences in the original coastal resources and urban development planning must be considered, the traditional parameters of economic development must be changed, the efficiency of coastline utilization must be improved, and urban clusters must be integrated.