青藏高原是长江、黄河以及跨境河流雅鲁藏布江、澜沧江和怒江的发源地，为东南亚和南亚约16亿人口提供重要的淡水资源。然而，青藏高原所经历的气温上升几乎是全球变暖速率的三倍，导致了冰川退缩、积雪减少、多年冻土层融化等现象。基于青藏高原迄今为止最全面的径流观测数据，研究揭示了青藏高原气候条件的转变显著影响了河流源区径流量的变化。结果表明：①五条河流源区的年平均气温呈稳定上升趋势，1998年后的变化趋势为每十年上升0.38 ℃，是1998年之前变化速率的三倍；②源区径流变化主要受降水变化的影响，1998年后长江、雅鲁藏布江、澜沧江和怒江源区径流呈下降趋势，变化幅度为每十年减少3 × 10⁹~5.9 × 10⁹ m³（每十年减少9.12%~16.89%）；③唐乃亥和兰州流域降水增加，导致径流以每十年8.04%和14.29%的速度增加。尽管黄河源区径流增加可能会缓解一些水资源问题，但是1998年以来青藏高原东南部河流源区径流下降趋势可能导致东南亚和南亚数十亿人面临水资源危机。

The Tibetan Plateau (TP) is the headwater of the Yangtze, Yellow, and the transboundary Yarlung Zangbo, Lancang, and Nujiang Rivers, providing essential and pristine freshwater to around 1.6 billion people in Southeast and South Asia. However, the temperature rise TP has experienced is almost three times that of the global warming rate. The rising temperature has resulted in glacier retreat, snow cover reduction, permafrost layer thawing, and so forth. Here we show, based on the longest observed streamflow data available for the region so far, that changing climatic conditions in the TP already had significant impacts on the streamflow in the headwater basins in the area. Our analysis indicated that the annual average temperature in the headwater basins of these five major rivers has been rising on a trend averaging 0.38 °C·decade⁻¹ since 1998, almost triple the rate before 1998, and the change of streamflow has been predominantly impacted by precipitation in these headwater basins. As a result, streamflow in the Yangtze, Yarlung Zangbo, Lancang, and Nujiang River headwater areas is on a decreasing trend with a reduction of flow ranging from 3.0 ×10⁹-5.9 ×10⁹ m³·decade⁻¹ (−9.12% to −16.89% per decade) since 1998. The increased precipitation in the Tangnahai (TNH) and Lanzhou (LZ) Basins contributed to the increase of their streamflows at 8.04% and 14.29% per decade, respectively. Although the increased streamflow in the headwater basins of the Yellow River may ease some of the water resources concerns, the decreasing trend of streamflow in the headwater areas of the southeastern TP region since 1998 could lead to a water crisis in transboundary river basins for billions of people in Southeast and South Asia.

・In addition to the accelerated rise of temperature, there has been a significant monthly increase from November to February since 1998.

・The Yurlang Zangbo, Lancang, and Yangtze River head water areas have experienced a decreasing trend of precipitation and streamflow since 1998.

・The Yellow River head water areas have experienced an increasing trend of precipitation and streamflow since 1998.

・Changes in streamflow in the Yurlang Zangbo, Lancang, and Yangtze River head water areas correlate well with changes in precipitation.

・Changes in streamflow in the Yellow River do not correlate well with precipitation due to reservoirs constructed on the river.