During the South-American Monsoon season, deep convective systems occur at the eastern flank of the Central Andes leading to heavy rainfall and flooding. We investigate the large- and meso-scale atmospheric dynamics associated with extreme discharge events (> 99.9th percentile) observed in two major river catchments meridionally stretching from humid to semi-arid conditions in the southern Central Andes. Based on daily gauge time series and ERA-Interim reanalysis, we made the following three key observations: (1) for the period 1940–2016 daily discharge exhibits more pronounced variability in the southern, semi-arid than in the northern, humid catchments. This is due to a smaller ratio of discharge magnitudes between intermediate (0.2 year return period) and rare events (20 year return period) in the semi-arid compared to the humid areas; (2) The climatological composites of the 40 largest discharge events showed characteristic atmospheric features of cold surges based on 5-day time-lagged sequences of geopotential height at different levels in the troposphere; (3) A subjective classification revealed that 80% of the 40 largest discharge events are mainly associated with the north-northeastward migration of frontal systems and 2/3 of these are cold fronts, i.e. cold surges. This work highlights the importance of cold surges and their related atmospheric processes for the generation of heavy rainfall events and floods in the southern Central Andes.

在南美季风季节，中部安第斯山脉中部东部侧部发生深对流系统，导致大量降雨和洪水。我们调查了安第斯中南部南部从湿润到半干旱的两个子午流经子午线延伸的大尺度和中尺度大气动力学，这些事件与极端排放事件（> 99.9％）相关。基于日尺度时间序列和ERA-Interim的再分析，我们得出以下三个主要观察结果：（1）在1940-2016年期间，南部半干旱地区的日排放量比北部潮湿地区的日排放量具有更明显的变化性。这是由于与潮湿地区相比，半干旱地区的中间（0.2年恢复期）和罕见事件（20年恢复期）之间的排放量比率较小；（2）根据对流层中不同水平的5天时间滞后序列的地势高度时间序列，40个最大排放事件的气候综合显示了冷潮的特征性大气特征；（3）主观分类表明，在40个最大的排放事件中，有80％主要与额叶系统的北-北向迁移有关，其中的2/3是冷锋，即冷潮。这项工作强调了冷涌及其相关的大气过程对于安第斯中南部南部发生强降雨事件和洪水的重要性。（3）主观分类表明，在40个最大的排放事件中，有80％主要与额叶系统的北-北向迁移有关，其中的2/3是冷锋，即冷潮。这项工作强调了冷涌及其相关的大气过程对于安第斯中南部南部发生强降雨事件和洪水的重要性。（3）主观分类表明，在40个最大的排放事件中，有80％主要与额叶系统的北-北向迁移有关，其中的2/3是冷锋，即冷潮。这项工作强调了冷涌及其相关的大气过程对于安第斯中南部南部发生强降雨事件和洪水的重要性。