Abstract: In the summer of 2022,abnormal high temperatures and drought in the Yangtze River Basin severely impacted China's natural environment.On 4 August,Dongting Lake had already entered the dry season,with the continuous exposure of lake bed,and disconnection even in the core area of the main lake body.In order to accurately monitor the spatiotemporal changes in the water of the East Dongting Lake wetland during this drought period,UAV sampling data and field survey data were used to evaluate the accuracy of three typical algorithms:MNDWI,AWEI,and CS-OTSU.Experimental results indicate that the CS-OTSU algorithm shows the highest mapping accuracy,user accuracy,overall classification accuracy and Kappa coefficient.It can accurately extract the dry flow of the main lake body and the exposed lake bed.The spatiotemporal change results of East Dongting Lake wetland water in August 2022 extracted by the CS-OTSU method show that the average water area decreased by 71.58% compared with the same period in 2021.The permanent water area decreased by 86.24%.From the beginning to the end of the month,more than half of the water body of the East Dongting Lake wetland had shrunk.Despite remaining stable,the water body boundary of the main flood channel was reflecting the severe impact of drought.The core area of the main lake dried up entirely,indicating the severe impact of this drought on the East Dongting Lake wetland.

Key words: Drought over Yangtze River Basin, Water body extraction, Water body change, East Dongting Lake Wetland