Mapping and Evaluation of the 2020 Catastrophic Floods in the Yangtze River Basin Using Sentinel-1 Imagery

Flood disaster is one of the natural disasters with the highest frequency in the Yangtze River, which caused immeasurable losses, particularly catastrophic floods in the Yangtze River Basin during July and August 2020. Nowadays, Synthetic aperture radar (SAR) imagery can monitor and evaluate floods in any weather conditions. In this paper, the spatial-temporal variations of the 2020 catastrophic flood are investigated and evaluated from Sentinel-1 date and Otsu thresholding method in the two perspectives of area disparity and flood duration. Four severe flood sections of the Yangtze River (Yueyang, Hankou, Jiujiang, Chizhou) are taken as study objects. Yueyang and Hankou sections are in the middle reach and the Jiujiang and Chizhou section are in the lower section. The results show that the average water body area in 2020 was 20.40% larger than that in 2019 in four sections of the Yangtze River. The upper sections are suffered more from floods for a longer time. The water area of four sections shows a highly positive correlation with the water level, which is the highest in Jiujiang Section, even to 0.9924. The four sections are affected by the flood events in 2020 with the order as follows: Yueyang section > Jiujiang section > Hankou section > Chizhou section.