It is a pleasure to thank M. Mann for helpful discussions, and both reviewers for their constructive comments. We gratefully acknowledge N. O. Garcia for providing the Paraná and Paraguay streamflow data, and UTE (Usinas y Transmisiones Eléctricas, Uruguay’s public utility company) for the Uruguay and Negro River data. This work was supported by NOAA Grants under the GOALS (NAG56022) and PACS (NA56GP0222) programs. This is publication number 4995 of UCLA’s Institute of Geophysics and Planetary Physics.
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