Abstract: Based on runoff data collected from the Tuotuohe and Zhimenda hydrological stations, we examined the historical runoff patterns over the past six decades, and analyzed the intensity and temporal characteristics of ENSO (El-Niño Southern Oscillation) events using the Oceanic Niño Index. We also investigated the response of runoff to ENSO events and explored the potential influence of ENSO events on runoff through the lens of sea-air coupling and its impact on atmospheric circulation. The findings revealed an oscillating increasing trend in runoff at both stations, particularly noticeable since 2000, indicating a significant upward trend in runoff. Analysis of the response of runoff in the source region of Yangtze River during ENSO events demonstrated a higher probability of runoff drying up during warm events between 1960 and 2000, regardless of the current year or the subsequent year. Conversely, during cold events, both stations exhibited a comparable probability of drying up in the current year and abundant or dry conditions in the following year. Notably, after 2000, runoff in the source region experienced a substantial increase. Prior to 1970 and after 2000, runoff in the region was positively correlated with ENSO events in terms of time-frequency structure. Following an ENSO event, abnormalities in the zonal and meridional atmospheric circulation occurred, subsequently affecting ocean heat and water vapor transport to the plateau. These changes ultimately impacted the precipitation and runoff patterns in the Qinghai-Tibet Plateau.

Key words: runoff, ENSO event, climate index, cross wavelet transform, source region of Yangtze River