Dry-Season Water Level Shift Induced by Channel Change of the River-Lake System in China's Largest Freshwater Lake, Poyang Lake

As a large open lake that connects to the middle reaches of Yangtze River, Poyang Lake, China, has experienced dramatic water level changes, especially during the dry periods (November-March) in recent years. For better understanding the shift of dry-season lake level, we quantified the variations induced by channel changes of the river-lake system (CCORLS). Attempts were achieved through establishing two Long Short-Term Memory (LSTM) based water level prediction models, combined hydrological data in the periods of 1956-2000 and 2006-2016. The results indicated that: (1) With reference to earlier (1956-2000) dry periods, the recent (2006-2016) mean water levels had an overall decreasing trend, with values of 0.04-1.26 m across the lake. (2) The response of water level to CCORLS was spatially heterogeneous, triggering a sharp reduction in the central to northern lake, an obvious reduction in the lake outlet, and a relatively smaller reduction in the southern lake. (3) The bottom topography alteration of Poyang Lake made a dominating contribution to decline the lake water levels, while the Yangtze River's mainstream channel near the lake played a minor role in the decrease of water level. Results shed light on the impact of systematic watercourse changes on the water level of a lake connected a river and enhanced understanding of the characteristics and mechanisms behind the hydrological changes of large freshwater lakes.