Spatiotemporal evolution and influencing factors of coastline in the Guangdong-Hong Kong-Macao Greater Bay Area from 1975 to 2018

Coastline transitionally extending from land to sea is the most densely populated area with the most frequent human activities. More than 50% of the global population and 60% of GDP are concentrated in the area less than 100 km away from the coastline. Coastline plays an important indicator role in sea level rise, coastal erosion, estuary siltation, wetland ecological resources, and coastal environment, etc. Remote sensing images were interpreted to acquire data about coastline of Guangdong-Hong Kong-Macao Greater Bay Area(GBA) from 1975 to 2018. Based on GIS platform, the spatio-temporal changes and influencing factors of shoreline were analyzed. The results reveal that the mainland coastline in GBA witnessed significant temporal and spatial changes, which could be divided into two stages. From 1975 to 1995, the length of shoreline increased significantly, the pattern of shoreline type changed significantly; after 1995, the coastline length increased slowly, but the construction land increased strongly. From 1975 to 2018, the coastline of GBA became more and more tortuous, and the fractal dimension increased. In terms of spatial position change, the coastline of the mainland continued to advance toward the sea, with an average rate of 9.91 m/a. The farthest extension to the sea occurred from Hongqimen to Jiaomen and from Hutiaomen to Jitimens with the maximum rate of 197.88 m/a. The development and utilization of the mainland coastline and the intervention of human activities on coastline evolution in GBA increased gradually. The main shorelines affected by human activities were port construction shoreline and reclamation aquaculture shoreline. The natural environment of GBA, such as topography and hydro-logical characteristics was the basis of coastline evolution. Social and economic development and policies were the important driving factors of coastline evolution. At the end of the 20th century, the development speed had the greatest impact on the coastline, and the development intensity was still the main factor at the beginning of the 21st century.