Abstract: Climate change has greatly impacted the runoff conditions in the source region of the Yangtze River in the past two decades. We analyzed the seasonal runoff variation, seasonal precipitation, and temperature variation based on measured hydro-meteorological data from the Tuotuo River hydrological station and meteorological station from 1960 to 2019. The cross wavelet transform is applied to examine the time-frequency variation and correlation among runoff, precipitation, and air temperature. Results reveal that the runoff of Tuotuo River in spring, summer, and autumn exhibited a significant increasing trend, with abrupt change points concentrated around 2006-2008. The increasing trend of seasonal precipitation was not significant, but the seasonal temperature displayed a marked rise that continues to the present. The correlation between summer runoff and precipitation was the most apparent, followed by autumn and spring. Temperature had a positive correlation with runoff, but it manifested differently on various time scales. Summer and autumn temperatures had the most significant effect on runoff. These findings provide important insights into the evolution law of seasonal runoff and hydrological response in the source region of the Yangtze River under the impacts of climate change.

Key words: seasonal runoff variation, Tuotuo River, precipitation, temperature, cross wavelet transform, multi-scale correlation