6. Conclusions
Through comparative analysis of the water area of Poyang Lake in the past 42 years, draw these conclusions:
1. During the 1977 to 2021 flood season, lake water areas at −9.14km2/a have a significant downward trend. In the dry season, the lake water area showed a significant downward trend with the rate of −17.52km2/a. The change point years of flood season water area are 2005 and dry season water is 2003.
2. Lake runoff, sediment, and precipitation significantly correlate with flood season water area. In the dry season, the sediment significantly correlates with the water area.
3. The analysis of satellite imagery confirms that in flood season, there is a direct correlation between the change of water area and the change of net outflow of the lake, and the net outflow is affected by river-lake interaction. Poyang lake is a classical river-connected drain lake. Flood or drought events in the mainstream of the Yangtze River will affect the blocking or reversing of the Yangtze River on the Poyang lake estuary, which affects the change of net outflow of the lake bringing the changes in water area.
4. In the dry season, based on the analysis of image and land use, the sediment deposition at the elevation of the estuarine entrance lake lakebed is raised, especially at the Ganjiang river estuary, affecting the water body shape. Meanwhile, after 2000, the TGD water impoundment operation at the end of the flood season on the upper Yangtze river affected the runoff of the lower reaches of the Yangtze River. That impaired the river lake interaction, made the area of Poyang Lake shrink in advance, made the water area shrank in advance, and affected the water area in the dry season.
Results show that the variation of water area in Poyang Lake is not only affected by the runoff of the Poyang Lake basin but also by the runoff of the Yangtze River main stream and the sediment inside the Poyang Lake basin. The downside does not consider the groundwater’s effect. Therefore, the water resource utilization in the Poyang Lake basin needs to consider the changes in the lake basin and the runoff outside the basin.