Characteristics of Mainland Coastline Changes in Southeast Asia during the 21st Century

Based on multitemporal Landsat images covering the entire coastal zone, a visual interpretation method was adopted to extract the coastlines of mainland Southeast Asia (MSA) in 2000 and 2015 referencing Google Earth images and global distribution of mangrove data. Coastline structures, coastline fractal dimensions, coastline change rates, and patterns of land-sea interchange were analyzed to reveal the spatial-temporal characteristics of mainland coastline changes in the 21st century. The results showed that (1) during the past 15 years, the length and percentage of natural coastline decreased from 15,440.24 km (83.33%) to 14,909.75 km (78.91%) and artificial coastlines increased at an average growth rate of 29.04% from 3088.79 to 3985.89 km; (2) the fractal dimensions of most areas in MSA tended to increase under interference driven by human activities, and the coastline morphology became more complex overall; (3) coastlines had obvious evolution, in which 18.54% of the coastline advanced toward the sea and 11.25% retreated toward land at average rates of +20.36 and -15.41 m.a(-1), respectively; and (4) the number of patches representing land-sea interchange reached 6607 so that the net land expansion area was 534.25 km(2) and among these regions, those larger than 1 km(2) accounted for only a small percentage (2.54%) of the total number but 79.41% of the total area. These hot spots were mainly concentrated in Myanmar, followed by Vietnam and Malaysia. Overall, the coastline of MSA was characterized by rapid artificial growth but still had a high percentage of naturalization. When it comes to developing the marine economy and addressing the ecological risk, the intensity of utilization and hardening of the coastline will likely increase.