Influence of mature El Nino-Southern Oscillation phase on seasonal precipitation and streamflow in the Yangtze River Basin, China

As one of the most influential oceanic and atmospheric oscillations in the Earth system, El Nino-Southern Oscillation (ENSO) has modulated numerous geophysical processes. This is particularly true for the Yangtze River Basin (YRB), which is vulnerable to Asian Monsoon and faces serious hydrological hazards. In this study, the co-variability between lag-lead precipitation and sea surface temperature anomalies was evaluated utilizing singular value decomposition (SVD) method. Moreover, certain teleconnections between ENSO and streamflow were identified by wavelet methods. In addition, the contribution of related atmospheric variables was revealed by composite analysis. Results indicate that there are strong associations in lag-lead seasons between the wet condition (dry condition) and September-November (December-February) mature ENSO phase. Significant common power and coherence signals between the ENSO indices and the streamflow occur in the 4-8, 8-16 and 16-32 seasonal scales. Meanwhile, the activity cycle of the ENSO indices ahead of streamflow increases from the mid-lower reaches to the source region. In addition, the Western Pacific Subtropical High is strengthened during the mature ENSO phase. Anomalous sinking motions and divergent water vapour flux occupy the YRB, reducing the precipitation and leading to the dry condition in the source region until the following March-May. On the other hand, ascending movements and abundant water vapour flux coming from northern Pacific, equatorial western Pacific and the Bay of Bengal result in the wet condition in the mid-lower reaches.