The Yangtze River Source Region has an area of 137,704 km2. Its mean annual runoff of 12.52 billion m3, which was recorded by the Chumda Hydrological Station in 1961-2000, accounts for only 0.13 percent of the Yangtze River's total annual streamflow. The extensive rivers, lakes, wetlands, glaciers, snow fields, and permafrost of the Yangtze River Source Region, as well as the re gion's vast alpine grasslands, play a critical role in storing and regulating the flow of water not only in the upper Yangtze River watershed of Qinghai, Sichuan, the Tibet Autonomous Region (TAR) (Tibet) and Yunnan, but also throughout the entire lower Yangtze River basin. Climate change has been the dominant factor in recent fluctuation in the volume of the Yangtze River Source Region's glacier resources. The Chumda Hydrological Station on the lower Tongtian River has registered a mean annual glacial meltwater of 1.13 billion m3 for the period 1961-2000, makes up 9 percent of the total annual runoff. Glacial meltwater makes up a significant percentage of streamfiow in the Yangtze River Source Region, the major rivers of the upper Yangtze River Source Region: the Togto, Dam Chu, Garchu, and Bi Chu (Bu Chu) rivers all originate at large glaciers along the Tanggula Range. Gla ciers in the Yangtze River Source Region are typical continental-type glaciers with most glacial meltwater flow occurring June-August; the close correlation between June-August river flows and temperature illustrates the important role of glacial meltwater in feeding rivers. Glaciers in the source region have undergone a long period of rapid ablation beginning in 1993. Ex amination of flow and temperature data for the 1961-2000 period shows that the annual melting period for glacial ice, snow, and frozen ground in the Yangtze River Source Region now begins earlier because of increasing spring temperatures, resulting in the reduction of summer flood season peak runoffs; meanwhile, increased rates of glacier ablation have resulted in more uneven an nual distribution of runoff in the source region. The annual glacial meltwater runoff in the Yangtze River Source Region is pro jected to increase by 28.5 percent by 2050 over its 1970 value with the projected temperature increase of 2 ℃ and a precipitation increase of 29 mm. As a critical source of surface water for agriculture on the eastern Qinghai-Tibet Plateau and beyond, the mass retreat of glaciers in the Yangtze River Source Region will have enormous negative impacts on fanning and livestock-raising ac tivities in upper Yangtze River watershed, as well as on the viability of present ecosystems and even socioeconomic development in the upper Yangtze River Basin.