Synchronous Characteristics of Precipitation Extremes in the Yangtze and Murray-Darling River Basins and the Role of ENSO

The floods caused by the extreme precipitation in the Yangtze River Basin (YRB) and the Murray-Darling River Basin (MDRB), the largest basins in China and Australia, have significant impacts on society and the regional economies. Based on spatial-temporal analysis of the daily precipitation extremes (DPEs) during 1982–2016, we found that for both basins, the whole-basin type DPEs have the highest proportion and a synchronous DPE inter-annual variation characteristic exists in the two basins, with the 3-yr running correlation coefficient of the annual DPE days (DPEDs) reaching almost 0.7 (significant at the 0.01 level). The El Nino-Southern Oscillation (ENSO), which is one of the most significant climate disturbance factors in the world, plays an important role in modulating the variability of the DPEs in the two basins. Singular value decomposition (SVD) analysis revealed that both the YRB and the MDRB’s whole-basin type DPEs are closely coupled with the procedure that the preceding winter eastern Pacific (EP) type El Nino faded to a central Pacific (CP) type La Nina. This means that the DPEs in the YRB and the MDRB may synchronously occur more frequently when the above process occurs. Owing to the atmosphere-ocean interaction from the east-west dipole sea surface temperature (SST) anomaly pattern, the atmospheric circulation disturbance exhibits a pattern in which the equatorial east Pacific region is a mass source anomaly with a higher pressure, drier air, and weaker convection, while the equatorial western Pacific region is a mass sink anomaly with a lower pressure, wetter air, and stronger convection. Moreover, two wave trains that originated from the tropical western Pacific were found to extend to the YRB and the MDRB. The interaction between the wave train's inter-phase dynamics and the water vapor transport disturbance results in ascent conditions and enhanced water vapor transport, which leads to the synchronous occurrence of DPEs in the YRB and the MDRB on an inter-annual scale.