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

Abstract

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.