Water resources in the Three-Rivers Headwater Region (TRHR), ‘China's Water Tower’, have declined in recent years. In particular, the causes and magnitude of declining runoff in the region remain unclear. This study investigated the recent climatic and hydrological trends in the TRHR. We also analyzed the influence of climate change on runoff decline. Meteorological and runoff data on the TRHR since 1961 were used. The results showed that ‘China's Water Tower’ is threatened by climate changes in several ways. The strong warming trend was the main driving factor for runoff decline. Moreover, the earlier thawing of snow and ice on frozen soil led to a significant decline in May runoff. The descending trend of the runoff coefficient suggests that basin storage and the mechanism of runoff generation may have changed appreciably. Climate warming has also caused recent degradation in the alpine wetland ecosystem and a considerable reduction in the runoff coefficient, thereby inducing a decreasing trend in river runoff. A common understanding of runoff decline due to climate change can be used in the planning and management for social, economic and cultural systems in China and surrounding countries.

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