Lake has an essential role in Earth’s hydrologic cycle. The changing of lake water areas shows the ecological health of lakes by instant feedback. Remote sensing monitoring reflects the changes in lake water intuitively. This study, based on remote sensing, combined with the hydrological data, meteorological data, and land use survey, investigated the Poyang lake water area changes from 1977 to 2021. Examined the relationship between the lake water area and the impact factor and analyzed the influence of river lake interaction on the lake water area. The results showed that: (1) From 1977 to 2017, the water area of Poyang Lake in flood season (June to September) and dry season (November to Next February) showed a significant downward trend by years. (2) In flood season, runoff, sediment, and precipitation significantly correlate with a water area. In the dry season, sediment significantly correlated with a water area. (3) The Three Gorges Dam water impoundment at the upper reaches of the Yangtze River weakened and eliminated the block and reverse flow of the Yangtze River on Poyang lake, causing the water area to decrease in advance at the end of the flood season after 2005, and decrease rapidly in the dry season after 2003. (4) The change in lakebed elevation caused by sedimentation and human activities also accelerated the shrinkage of the water area. Results demonstrated that the variation of river lake interaction is the primary cause of the Poyang Lake water area’s dramatic change.

Lake has an important role of Earth’s hydrologic cycle. The changing of lake water area shows the ecological health of lakes by instant feedback. Most analyses of long-term monitoring of lake area are not comprehensive enough, This study based on the remote sensing images from 1977 to 2021, combined with the Keyhole satellite data, hydrographic survey, meteorology monitoring and land use change survey, investigated the Poyang lake water area changes. Moreover, examined the response relationship between lake water area and the impact factor, analyzed the influence of river lake interaction on lake water area.The results showed that: (1) From 1977 to 2017, the water area of Poyang Lake in flood season (June to September) and dry season (November to Next February) showed a significant downward trend by years. (2) In flood season, runoff, sediment, precipitation has significant correlation with water area. In dry season, sediment showed a significant correlation with water area. (3) The Three Gorges Dam water impoundment at the upper reaches of the Yangtze River weakened eliminated the blocking or reversing flow from the Yangtze River, caused the water area decreased in advance at the end of flood season after 2005, and decreased rapidly in dry season after 2003. (4) The change of lakebed elevation caused by sedimentation and human activities also accelerated the shrinkage of water area. Result demonstrated that the variation of river lake interaction is the primary cause of Poyang Lake water area dramatic change.

Investigating the changes in streamflow regimes is useful for understanding the mechanisms associated with hydrological processes in different watersheds and for providing information to facilitate water resources management. In this study, we selected three watersheds, i.e., Sandu River, Hulu River, and Dali River on the Loess Plateau, to examine the changes in the streamflow regimes and to determine their responses to different soil and water conservation measures (terracing, afforestation, and damming). The daily runoff was collected continuously by three hydrological gauges close to the outlets of the three watersheds from 1965 to 2016. The eco-surplus, eco-deficit, and degree of hydrological change were assessed to detect hydrological alterations. The Budyko water balance equation was applied to estimate the potential impacts of climate change and human activities on the hydrological regime changes. Significant decreasing trends (P < 0.05) were detected in the annual streamflow in the Sandu and Dali River watersheds, but not in the Hulu River watershed where afforestation dominated. The annual eco-surplus levels were low and they decreased slightly at three stations, whereas the eco-deficit exhibited dramatic increasing trends in the Sandu and Dali River watersheds. In the Sandu River watershed (dominated by terraces), the runoff exhibited the most significant reduction and the eco-deficit was the highest among the three watersheds. The integral degrees of hydrological change were higher in the Sandu River watershed than the other two watersheds, thereby suggesting substantial variations in the magnitude, duration, frequency, timing, and rate of change in the daily streamflow. In the Dali River watershed (dominated by damming), the changes in the extreme flow were characterized by a decreasing number appearing in high flow. In these watersheds, human activities accounted for 74.1% and 91.78% of the runoff reductions, respectively. In the Hulu River watershed (dominated by afforestation), the annual runoff exhibited an insignificant decreasing trend but with a significant increase in the low flow duration. Rainfall changes accounted for 64.30% of the runoff reduction.