Spatial Heterogeneity and Temporal Variation of Water Levels in Dongting Lake

To quantify the spatiotemporal patterns of the water-level variations in the study area, we conducted cluster analysis of the temporally varying measurements across multiple hydrological stations. The temporal trends and change points were analyzed, followed by IHA-RVA quantification of the water-level alterations before and after change points. Cluster analysis demonstrated the following. (1) Hydrological stations segregate into two distinct groups at the Euclidean distance threshold d = 5, and into three clusters at d = 4, confirming the pronounced west–east heterogeneity in the lake. (2) The hydrological alteration degrees exhibit considerable variation across the lake’s sub-lakes (Qili, Muping, South Dongting, East Dongting), with marked heterogeneity persisting even among representative monitoring stations within individual sub-lakes. The water-level regimes in Qili Lake can be partitioned into two distinct periods, before and after the change point, exhibiting the highest hydrological alteration degree across the lake. Representative stations of the other sub-lakes fall into three periods. During the first phase of hydrological alteration, Zhouwenmiao, Jinshi, and Chenglingji exhibit moderate alteration. Throughout the second alteration phase, all the representative stations consistently exhibit moderate alteration, although significant heterogeneity emerges across hydrological indicators among the sub-lakes. (3) Downstream of Yangliutan station, the longitudinal profile exhibits terraced morphology, segmented into three distinct levels by two hydraulic knickpoints. This geomorphic configuration primarily controls both the localized stage reductions and the maintenance of elevated upstream water levels during dry seasons. Confronting the persistent dry-season stage declines at Yingtian Station, enhanced monitoring and conservation of terraced transition zones in South Dongting Lake must be prioritized, with implementation of the zoned control principle for water-level governance and lake management. This study establishes a scientific foundation for the protection and governance of Dongting Lake, thereby advancing sustainable utilization of its water resources.