Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes

CASTINO, F.; BOOKHAGEN, B.; DE LA TORRE, A.

CLIMATE DYNAMICS

SPRINGER

Lugar: Berlin; Año: 2020 vol. 55 p. 3485 - 3505

0930-7575

During the South-American Monsoon season, deep convective systems occur at the eastern flank of the Central Andes leadingto heavy rainfall and flooding. We investigate the large- and meso-scale atmospheric dynamics associated with extremedischarge events (> 99.9th percentile) observed in two major river catchments meridionally stretching from humid to semiaridconditions in the southern Central Andes. Based on daily gauge time series and ERA-Interim reanalysis, we made thefollowing three key observations: (1) for the period 1940-2016 daily discharge exhibits more pronounced variability in thesouthern, semi-arid than in the northern, humid catchments. This is due to a smaller ratio of discharge magnitudes betweenintermediate (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 coldsurges based on 5-day time-lagged sequences of geopotential height at different levels in the troposphere; (3) A subjectiveclassification revealed that 80% of the 40 largest discharge events are mainly associated with the north-northeastward migrationof frontal systems and 2/3 of these are cold fronts, i.e. cold surges. This work highlights the importance of cold surgesand their related atmospheric processes for the generation of heavy rainfall events and floods in the southern Central Andes.