Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes
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Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes F. Castino1 · B. Bookhagen1 · A. de la Torre2 Received: 22 December 2019 / Accepted: 8 September 2020 / Published online: 16 September 2020 © The Author(s) 2020
Abstract 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 semiarid 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. Keywords South American monsoon system · Cold surges · Orographic barrier · Mesoscale convective systems · Extreme discharge · Daily-discharge time series ERA-interim
1 Introduction In high-mountain regions strong convective events lead to high discharge often resulting in floods that critically impact local infrastructures and landscape causing economic and population losses (Wolman and Miller 1960; Plate 2002). This is particularly true for the intermediate elevations of the eastern Central Andes that are exposed to the South American Monsoon System (SAMS) (Zhou and Lau 1998; Vera et al. 2006; Silva and Carvalho 2007; Marengo et al. 2012). Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05458-1) contains supplementary material, which is available to authorized users. * F. Castino castino@uni‑potsdam.de 1
Institute of Geosciences, University of Potsdam, Potsdam, Germany
Faculty of Engineering, LIDTUA, Austral University and CONICET, Pilar, Buenos Aires, Argentina
2
The intermontane basins of northwestern Argentina constitute part of the Andean tributaries of the La Plata River, the second largest river basin in South America that flows across one of the most populated and economically relevant areas of the continent. In this region, heav
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