Spatiotemporal change of lake shrinkage and its response to the unprecedented heat waves in the middle and lower Yangtze River Basin

Due to the joint influence of human activities and climate change, lakes experience significant shrinkage or expansion, posing enormous challenges for water resource management and the ecological balance of lake ecosystems. As an important region abundant in water resources in China, the balance of water resources in the middle and lower Yangtze River Basin (MLY) is crucial for region sustainable development. However, to date, few studies have quantitatively analysed the lake area during heat waves in the MLY. To fill this gap, this study selected the summer of 2022, which encountered unprecedented heat waves, to analyse the changes of lake area in the MLY. Specifically, Sentinel-1 images were used as data sources, and the Random Forest (RF) model was applied to extract the monthly area of 62 lakes (area >10 km2) in the MLY from 2019 to 2022. The results showed that: (1) Compared to the Support Vector Machine (SVM) model and the Otsu method, the RF model had the highest accuracy, with its accuracy and Kappa coefficient in the testing samples of 97.14% and 0.94, respectively. During the period from June to September in 2022, the total area of 62 lakes decreased by 3475.50 km2. (2) Compared to the same period in the summer of 2019–2021, 23 lakes (37.10%) were observed to experience shrinkage. Among them, the area of Poyang Lake and Dongting Lake decreased to the level of the previous winter dry seasons in August 2022. (3) Temperature was the most important meteorological factor that caused changes in the lake area in the MLY, compared to precipitation, evaporation, and runoff. This research can help understand the impact of climate change on lakes and provide references for decision-making in the MLY to formulate the strategies of water resource management under the changing climate.