Unusual Recent Prolonged Low Flow in the Moqu River, Northeastern Tibetan Plateau, Inferred from Tree-Ring Width Variations

The runoff of Moqu river in Zoige, one of most important water conservation ecological function areas in the upper reaches of the Yellow River, located in the north-east of the Tibetan Plateau, is highly sensitive to climate change. However, the current understanding of the long-term changes in the hydrology of this rives is still fragmentary. In this study, we created a regional tree-ring width chronology from two sample sites in Moqu River Basin and analysed the relationships between tree-ring width, climate, and runoff. We found significant positive correlations between tree-ring width and runoff in multiple months, the highest correlation coefficient occurred with annual runoff from previous July to current June (r = 0.617, 1981-2013). Based on this highly significant (p < 0.01) relationship, we reconstructed runoff variations of Moqu River for the period 1672 to 2019. The reconstructed runoff showed unusual prolonged and frequent low flow periods in recent decades. We found that the continuous low precipitation and the high temperature in the context of global warming are the main reasons for the abnormal runoff in recent decades. We assume that a weakening of the Indian summer monsoon (ISM) circulation system may be the key large-scale factor that caused the unusually prolonged low flow. With global warming, the weakening of ISM intensity leads to reduced water vapor transport from the tropical Indian Ocean to High Asia, resulting in less precipitation and low runoff events in Zoige. Our reconstruction improves the understanding of regional runoff variability over multiple timescales, and also provides a scientific basis for the protection, development, and utilization of water resources related to ongoing global warming.