Exploring the changes and drivers of open-surface water bodies is essential for the well-being of humanity in the face of global climate change. As one of the core areas in the Qinghai-Tibet Plateau (QTP), the headwater region of the Yangtze, Yellow, and Lancang Rivers is a water source for billions of people in Asia. However, previous studies failed to provide complete open-surface water data and watershed-level analysis for this region. Utilizing the Google Earth Engine platform and vegetation-water algorithm, we interpreted open-surface water bodies from all available Landsat surface reflectance data and generated annual 30-m water body frequency maps for 1987–2021, which is a complete open-surface water body dataset in the study area. Compared to the Joint Research Centre’s Global Surface Water dataset, the dataset in our study maintains consistency in 90.1 % of pixels and achieved correct classification in 74.6 % of pixels within the inconsistent areas. The perennial water body area exhibited an increase from 232,335 to 293,534 ha. Instead, the seasonal water body area notably declined from 223,809 to 182,003 ha. The Yangtze River headwater region shows an increase in perennial water bodies, with no significant variation in seasonal water bodies. The Yellow River headwater region experiences an increase in perennial water bodies but a decrease in seasonal water bodies. Remarkably, in the Lancang River headwater region, with lower water body density, both the perennial and seasonal water body areas decreased by 36.8 % and 48.8 %, respectively. The divergent changes in the headwater region of the Three Rivers are primarily attributed to spatial heterogeneity in the temperature effects on water bodies. Anticipated increases in the temperature are expected to amplify these differences. Our findings suggest that climate-driven open-surface water body changes are ongoing in this core area in the QTP, threatening the water security of densely populated East and Southeast Asia in the future.