Abstract: To reveal the spatiotemporal evolution of the water surface area of Hulun Lake over the past 30 years and its dominant driving factors, and to provide a scientific basis for watershed ecological protection and optimal allocation of water resources, this study used Landsat TM/OLI remote sensing images from 1991 to 2019, employed the Modified Normalized Difference Water Index (MNDWI) and GIS spatial analysis techniques to extract the time series of the lake's water surface area, and combined meteorological and hydrological data with Pearson correlation analysis to quantitatively evaluate the impacts of natural climate and human activities on changes in the lake's water surface area. The results showed that the evolution of the water surface area of Hulun Lake from 1991 to 2019 underwent three stages: a high-level fluctuation period, a continuous shrinkage period, and a recovery and adjustment period. The water surface area ranged from 1798.0 to 2 389.0 km², with a range of 591.0 km². There was no significant linear correlation between the water surface area of Hulun Lake and the annual mean temperature or annual precipitation. A single climatic factor could not fully explain the complex evolution of Hulun Lake over the past 30 years. The shrinkage of the water surface area of Hulun Lake from 2000 to 2010 was mainly driven by the sharp reduction in upstream inflow into the lake, especially the frequent drying-up of the Kherlen River, whereas the rapid recovery of the water surface area after 2010 was primarily attributed to the effective implementation of ecological water replenishment projects such as the “Diverting River Water to Recharge the Lake” project. The study indicated that the evolution mechanism of the water surface area of Hulun Lake had shifted from being dominated by natural hydrology to being jointly driven by natural and artificial regulation. Therefore, it was recommended that the joint dispatch of water resources across the entire basin and the dynamic ecological water replenishment mechanism be strengthened in the future, so as to ensure the long-term stability of the lake ecosystem.

Key words: water surface area, spatiotemporal evolution, dynamic monitoring, driving mechanism, Hulun Lake