TY - JOUR A1 - Castino, Fabiana A1 - Bookhagen, Bodo A1 - Strecker, Manfred T1 - River-discharge dynamics in the Southern Central Andes and the 1976-77 global climate shift JF - Geophysical research letters N2 - Recent studies have shown that the 1976-77 global climate shift strongly affected the South American climate. In our study, we observed a link between this climate shift and river-discharge variability in the subtropical Southern Central Andes. We analyzed the daily river-discharge time series between 1940 and 1999 from small to medium mountain drainage basins (10(2)-10(4) km(2) ) across a steep climatic and topographic gradient. We document that the discharge frequency distribution changed significantly, with higher percentiles exhibiting more pronounced trends. A change point between 1971 and 1977 marked an intensification of the hydrological cycle, which resulted in increased river discharge. In the upper Rio Bermejo basin of the northernmost Argentine Andes, the mean annual discharge increased by 40% over 7 years. Our findings are important for flood risk management in areas impacted by the 1976-77 climate shift; discharge frequency distribution analysis provides important insights into the variability of the hydrological cycle in the Andean realm. Y1 - 2016 U6 - https://doi.org/10.1002/2016GL070868 SN - 0094-8276 SN - 1944-8007 VL - 43 SP - 11679 EP - 11687 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Castino, Fabiana A1 - Bookhagen, Bodo A1 - Strecker, Manfred T1 - Rainfall variability and trends of the past six decades (1950-2014) in the subtropical NW Argentine Andes JF - Climate dynamics : observational, theoretical and computational research on the climate system N2 - The eastern flanks of the Central Andes are characterized by deep convection, exposing them to hydrometeorological extreme events, often resulting in floods and a variety of mass movements. We assessed the spatiotemporal pattern of rainfall trends and the changes in the magnitude and frequency of extreme events (ae95th percentile) along an E-W traverse across the southern Central Andes using rain-gauge and high-resolution gridded datasets (CPC-uni and TRMM 3B42 V7). We generated different climate indices and made three key observations: (1) an increase of the annual rainfall has occurred at the transition between low (< 0.5 km) and intermediate (0.5-3 km) elevations between 1950 and 2014. Also, rainfall increases during the wet season and, to a lesser degree, decreases during the dry season. Increasing trends in annual total amounts characterize the period 1979-2014 in the arid, high-elevation southern Andean Plateau, whereas trend reversals with decreasing annual total amounts were found at low elevations. (2) For all analyzed periods, we observed small or no changes in the median values of the rainfall-frequency distribution, but significant trends with intensification or attenuation in the 95th percentile. (3) In the southern Andean Plateau, extreme rainfall events exhibit trends towards increasing magnitude and, to a lesser degree, frequency during the wet season, at least since 1979. Our analysis revealed that low (< 0.5 km), intermediate (0.5-3 km), and high-elevation (> 3 km) areas respond differently to changing climate conditions, and the transition zone between low and intermediate elevations is characterized by the most significant changes. KW - Extreme rainfall KW - South American Monsoon System KW - Central Andes KW - Quantile regression KW - Rain gauges KW - CPC-uni KW - TRMM KW - Orographic barrier Y1 - 2017 U6 - https://doi.org/10.1007/s00382-016-3127-2 SN - 0930-7575 SN - 1432-0894 VL - 48 SP - 1049 EP - 1067 PB - Springer CY - New York ER - TY - JOUR A1 - Castino, Fabiana A1 - Bookhagen, Bodo A1 - Strecker, Manfred T1 - Oscillations and trends of river discharge in the southern Central Andes and linkages with climate variability JF - Journal of hydrology N2 - This study analyzes the discharge variability of small to medium drainage basins (10(2)-10(4) km(2)) in the southern Central Andes of NW Argentina. The Hilbert-Huang Transform (HHT) was applied to evaluate non-stationary oscillatory modes of variability and trends, based on four time series of monthly normalized discharge anomaly between 1940 and 2015. Statistically significant trends reveal increasing discharge during the past decades and document an intensification of the hydrological cycle during this period. An Ensemble Empirical Mode Decomposition (EEMD) analysis revealed that discharge variability in this region can be best described by five quasi-periodic statistically significant oscillatory modes, with mean periods varying from 1 to 20 y. Moreover, we show that discharge variability is most likely linked to the phases of the Pacific Decadal Oscillation (PDO) at multi-decadal timescales (similar to 20 y) and, to a lesser degree, to the Tropical South Atlantic SST anomaly (TSA) variability at shorter timescales (similar to 2-5 y). Previous studies highlighted a rapid increase in discharge in the southern Central Andes during the 1970s, inferred to have been associated with the global 1976-77 climate shift. Our results suggest that the rapid discharge increase in the NW Argentine Andes coincides with the periodic enhancement of discharge, which is mainly linked to a negative to positive transition of the PDO phase and TSA variability associated with a long-term increasing trend. We therefore suggest that variations in discharge in this region are largely driven by both natural variability and the effects of global climate change. We furthermore posit that the links between atmospheric and hydrologic processes result from a combination of forcings that operate on different spatiotemporal scales. (C) 2017 Elsevier B.V. All rights reserved. KW - River discharge KW - Central Andes KW - Empirical Mode Decomposition KW - PDO KW - Climate variability KW - Global climate change Y1 - 2017 U6 - https://doi.org/10.1016/j.jhydrol.2017.10.001 SN - 0022-1694 SN - 1879-2707 VL - 555 SP - 108 EP - 124 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Castino, Fabiana A1 - Bookhagen, Bodo A1 - De la Torre, Alejandro T1 - Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes JF - Climate dynamics : observational, theoretical and computational research on the climate system N2 - 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. KW - South American monsoon system KW - cold surges KW - orographic barrier KW - mesoscale convective systems KW - extreme discharge KW - daily-discharge time KW - series ERA-interim Y1 - 2019 U6 - https://doi.org/10.1007/s00382-020-05458-1 SN - 0930-7575 SN - 1432-0894 VL - 55 IS - 11-12 SP - 3485 EP - 3505 PB - Springer CY - Berlin ; Heidelberg [u.a.] ER -