Analysis of extreme drought characteristics and vegetation anomaly response mechanism in Poyang Lake in 2022 based on multisource remote sensing

The seasonal rhythm of lake ecosystems is crucial for their functionality. In 2022, the extreme drought experienced by Poyang Lake garnered significant attention due to its severe timing anomaly, which imposed a unique disturbance on the ecosystem. This study aims to reveal the characteristics and causes of this anomalous drought and to elucidate its driving mechanisms on the lake area's vegetation dynamics. By integrating data from Sentinel-1 SAR and MODIS (2001-2022) and employing methods such as the Mann-Kendall test and wavelet analysis, this research analyzes the dynamic response of the hydro-vegetation system in Poyang Lake during 2022. The results indicate that: (1) In 2022, the water surface area of Poyang Lake began to decline sharply starting in July, which is historically the high-water period. The area contracted to less than 450 km² by November, confirming the extreme anomaly in the drought's timing. The Vegetation Condition Index (VCI) showed a significant change-point and an accelerating upward trend after August, forming an “anomalous greening” phenomenon that was highly synchronized with the water area shrinkage. (2) Wavelet analysis reveals that the hydro-vegetation coupling relationship in 2022 broke the historical dominant period of approximately 30-40 months, transitioning into a short-period coupling mode, with the phase relationship also being altered. (3) Causal analysis confirms that the combination of extremely high temperatures and low precipitation in the Yangtze River Basin, along with a sharp reduction in upstream inflow, led to rapid mudflat exposure, providing favorable conditions for the rapid colonization and growth of drought-tolerant vegetation. The findings of this study provide a new scientific basis for assessing and managing the responses of similar ecosystems under future climate change.