Analyzing spatio-temporal changes in the shoreline morphology of Xiamen City in the context of urbanization

China boasts long shorelines and abundant marine resources. Xiamen, a coastal city in China, has seen significant changes in its shorelines in recent years due to an increase in activities including port construction, coastal industry, and coastal tourism development. Hence, efficiently and accurately determining the spatio-temporal changes in Xiamen's shoreline holds critical research value and practical significance. This study extracted information on the shorelines from the Landsat remote sensing images in 2005, 2010, 2015, and 2020 using the object-oriented method. Then, it delved into the spatio-temporal evolution of shoreline length, shoreline morphology, and land area changes. The results reveal significant spatio-temporal changes in Xiamen’s shoreline over the 15 years. The shoreline length changed quickly and then moderately, peaking from 2010 to 2015, with an average rate as high as 4.1 km/a, primarily in the vicinity of Dadeng Island and Haixiang Pier. The shoreline morphology tended to be flattened year by year, with the most pronounced changes observed in Huli District. From 2005 to 2020, the land area of Xiamen increased approximately 24.5 km², with the most significant increase occurring in Xiang’an District. The changes in the shoreline were influenced by many factors, predominantly including population growth, economic development, and the introduction and change of policies.