Grassland ecosystems provide a range of services in semi-arid and arid regions. However, they have significantly declined due to overgrazing and desertification. In the current study, we employed Landsat time series data (TM, OLI, OLI-2) spanning from 1990 to 2024, combined with vegetation indices such as NDVI and SAVI, along with NDWI and digital elevation models (DEMs), to analyze land cover dynamics in the Ugii Lake watershed area, Mongolia. By integrating multisource remote sensing data into the advanced XGBoost (extreme gradient boosting) machine learning algorithm, we achieved high classification accuracy, with overall accuracies exceeding 94% and Kappa coefficients greater than 0.92. The results revealed a decline in montane grasslands (−6.2%) and an increase in other grassland types, suggesting ecosystem redistribution influenced by climatic and anthropogenic factors. Cropland exhibited resilience, recovering from a significant decline in the 1990s to moderate growth by 2024. Our findings highlight the stability of barren land and underscore pressures from ecological degradation and human activities. This study provides up-to-date statistical data to support decision-making in the conservation and sustainable management of grassland ecosystems in Mongolia under changing climatic conditions.

This study investigates the hydrological, ecological, and socio-economic responses of Ugii Lake—a freshwater body in semi-arid Central Mongolia—to climate variability and anthropogenic pressures. Seasonal field surveys conducted during the spring, summer, and fall of 2023–2024 revealed notable spatial and temporal variation in water quality, with pH ranging from 7.54 to 8.87, EC from 316 to 645 µS/cm, and turbidity between 0.36 and 5.76 NTU. Total dissolved solids (TDS) values and ionic compositions indicated increased salinization in some zones, particularly those exposed to high evaporation and shoreline disturbance. Heavy metal analysis identified elevated levels of aluminum, manganese, and zinc at several sampling points; however, concentrations generally remained within national environmental standards. Vegetation surveys showed that disturbed areas—especially those affected by grazing and tourism—exhibited reduced native plant diversity and dominance of invasive species. Socio-economic interviews with local herders and stakeholders indicated that 67.3% of households experienced declining livestock productivity, and 37.1% reported increased allergies or respiratory symptoms linked to deteriorating environmental conditions. Despite some ongoing conservation efforts, respondents expressed dissatisfaction with enforcement and impact. These findings highlight the need for community-driven, integrated lake management strategies that address environmental degradation, climate adaptation, and rural livelihood security.