Mechanisms controlling storage capacity dynamics in China’s largest freshwater lake

Poyang Lake is the largest freshwater lake in China, yet mechanisms controlling its storage capacity variations remain poorly investigated. Here we show that lake storage capacity dynamics are mainly driven by jacking force and outlet channel erosion, based on 39-year daily in situ observations (1980-2018). A lower water level at the lake outlet and a diminished jacking force in the Yangtze River can be attributed to the upstream dams storing water between August and October; consequently, more water from Poyang Lake flows out, causing the impairment of storage capacity. Furthermore, channel degradation near the outlet is likely due to the severe sand mining and hungry-water-driven Yangtze channel erosion, the latter of which implies an enhanced outlet channel scour. As a result, the lake storage capacity has been substantially weakened. Our findings further the understanding of the downstream lake storage capacity responses to dam operation and human activities and have important implications for lake ecology and flood management in large dammed river-lake systems.