Possible causes of the flooding over south China during the 2015/2016 winter

Abstract

Sequential heavy rainfall clusters and resultant severe winter flooding was observed over South China during the 2015/2016 super El Niño event. In the present, the intra‐seasonal oscillations (ISOs) related with heavy rainfall over East Asia from late autumn to early winter in 2015/2016 were investigated using the daily in situ rainfall records and the NCEP‐DOE Reanalysis data set. Results suggested that the successive heavy winter rainfall events in 2015/2016 were contributed by the ISOs with significant periods of 10–25 and 30–45 days. The wet phase of 10–25‐day ISO was jointly induced by the anomalous convergence of the low‐level water vapour associated with the tropical–subtropical interaction and the upper‐level divergence attributed to the eastwards propagating wavetrain. However in the wet phase of the 30–45‐day ISO, the anomalous upper‐level divergence was possibly caused by the weaker East Asian trough and the stronger barotropic westerly in subtropics. The 30–45‐day ISO can facilitate the eastwards propagation of the 10–25‐day ISO by providing a benefit upper‐level waveguide. Afterwards, the low‐level southwesterly surrounding the Tibetan Plateau gets enhanced to bring more moisture into South China where the winter flooding was serious in 2015/2016. In contrast, the more‐than‐normal winter rainfall was weaker in the super El Niño of 1997/1998 due to the lack of the 30–45‐day ISO. Therefore, the strongest winter rainfall anomaly over SC was ascribed to the superposition between the wet phases of 10–25 and 30–45‐day ISOs in 2015/2016.