Satellite observed rapid inland aquaculture expansion in Jianghan Plain, China from 2016 to 2022

Inland freshwater aquaculture which includes a new crop-aquaculture system accounts for 77 % of aquaculture production worldwide and contributed significantly to the global demand for fish products. Previous aquaculture monitoring efforts, however, mainly focused on coastal aquaculture ponds and hardly covered inland freshwater aquaculture areas. Here, based on the time-series Sentinel-1 and 2 data and the Google Earth Engine (GEE) platform, we developed a hierarchical framework for mapping inland freshwater aquaculture with different aquaculture types (both aquaculture ponds and rice-crayfish fields) in the Jianghan Plain (JHP), one of the most important inland freshwater aquaculture regions in China. First, we constructed two phenological temporary windows (T1 and T2) and used an automatic threshold extraction method (OTSU approach) to generate potential aquaculture layers in both two temporary windows. Second, based on the potential aquaculture layer in T1, the actual aquaculture was further distinguished from other water bodies (e.g., lakes, rivers, and ditches) by combining spectral and texture features and utilizing a random forest classifier from 2016 to 2022. Finally, by the differences in variations in aquaculture ponds and rice-crayfish fields in T1 and T2, we generated annual 10m maps of fine aquaculture area in the Jianghan Plain from 2017 to 2022, with overall accuracies (OA) of 87.5 %–98.7 % and Kappa coefficients of 0.81–0.98. We found a significant increase in the total aquaculture area in  the JHP, from 2266 ± 66 km² in 2016 to 4766 ± 111 km² in 2022, with rice-crayfish fields contributing the most, mainly related to a series of stimulus policies. This study proposed a novel framework for monitoring complex inland freshwater aquacultures over large areas and revealed the rapid expansion of inland aquaculture in South China.