Thirty-year changes of the coastlines, wetlands, and ecosystem services in the Asia major deltas

Coastal zones are usually composed of coastlines and coastal wetlands and are among the most productive and dynamic ecosystems. However, the deltas are seldom detected and compared in detail at the continental scale to investigate the spatiotemporal evolution of coastline migration and coastal wetlands. Here we detected and compared the spatiotemporal changes in coastlines, wetlands, and ecosystem services in major deltas in Asia, including the Yellow River Delta (YRD), Yangtze River Delta (YAD), Pearl River Delta (PRD), Red River Delta (RRD), Mekong River Delta (MERD), Chao Phraya River Delta (CPRD), Mahanadi River Delta (MARD), Krishna River Delta (KRD), and Indus River Delta (IRD). We used time series remote sensing images from 1990 to 2019 to derive coastline and wetland information for the nine coastal zones. The ecosystem service value coefficients were applied to explore the ecosystem services characteristics of wetland changes in coastal areas. We found that the coastlines of the deltas in the study area changed less in the bedrock and sandy coasts, while the coastlines in the silty delta coasts changed more from 1990 to 2019. The interannual dynamics of coastal wetland areas in nine major deltas over the nearly 30 years can be divided into three periods: decreasing variability (1990-2005), increasing variability (2005-2015), and increasing volatility (2015-2019). Ecosystem services had an overall downward trend. These findings complement the official database of coastal planning and have substantial guiding implications for adjusting coastal management regulation policies.