Mapping China’s coastal aquaculture ponds expansion with sentinel-2 images during 2017–2021

ABSTRACTAccurately mapping large-scale areas of aquaculture ponds along China’s coastal areas is challenging. This study proposes a multi-featured decision tree method that incorporates multi-spectral indices, water inundation frequency (WIF), and object-oriented rules to extract aquaculture ponds in coastal zones using 65332 Sentinel-2 images on the GEE platform. The proposed method was validated, with the average overall accuracy of the extraction results from 2017 to 2021 reaching 90.80%, and an average F1 Score of 0.91. The results of this study indicate that the overall area of aquaculture ponds in China's coast in 2021 was 7633.83 km2, mainly located in coastal bay estuaries in Shandong Province, Jiangsu Province and Guangdong Province. In recent years, the area of coastal ponds for aquaculture in China has shown a decreasing trend, with an average annual decrease of 235.65 km2. The analysis combined with land use data shows that the ponds that have been reduced in the past five years have mainly been converted to abandoned aquaculture ponds, wetlands, and other land use types.