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.