The quantitative attribution of climate change to runoff increase over the Qinghai-Tibetan Plateau

Runoff from the Qinghai-Tibetan Plateau, a major global water tower, is crucial to regional hydrological processes and the availability of water for a large population living downstream. Climate change, especially changes in precipitation and temperature, directly impacts hydrological processes and exacerbates shifts in the cryosphere, such as glacier and snow melt, leading to changes in runoff. Although there is a consensus on increased runoff due to climate change, it is still unclear to what extent precipitation and temperature contribute to runoff variations. This lack of understanding is one of the primary sources of uncertainty when assessing the hydrological impacts of climate change. In this study, a large-scale, high-resolution, and well-calibrated distributed hydrological model was employed to quantify the long-term runoff of the Qinghai-Tibetan Plateau, and the changes in runoff and runoff coefficient were analyzed. Furthermore, the impacts of precipitation and temperature on runoff variation were quantitatively estimated. The results found that runoff and runoff coefficient decreased from southeast to northwest, with mean values of 184.77 mm and 0.37, respectively. Notably, the runoff coefficient exhibited a significant increasing trend of 1.27 %/10 yr (P < 0.001), while the southeastern and northern regions of the plateau showed a declining tendency. We further showed that the warming and humidification of the Qinghai-Tibetan Plateau led to an increase in the runoff by 9.13 mm/10 yr (P < 0.001). And precipitation is a more important contributor than temperature across the plateau, contributing 72.08 % and 27.92 % to the runoff increase, respectively. At the basin scale, the influence of precipitation and temperature on runoff varies among basins, with the Daduhe basin and the Inner basin being the most and least influenced by precipitation, respectively. This research analyses historical runoff changes on the Qinghai-Tibetan Plateau and provides insights into the contributions of climate change to runoff.