Anatomies of extreme Paraná River floods: Contributions of different time scales

ANDRÉS ANTICO; MARÍA EUGENIA TORRES; HENRY DIAZ

Santa Fe

Jornada; IV Jornada Multidisciplinar de Investigación; 2015

Facultad de Ingeniería y Ciencias Hídricas, Universidad Nacional del Litoral

The present study provides the first complete examination of how different time scales contributed to generate the four largest observed floods of the Paraná River (1905, 1983, 1992 and 1998). Flood-flow peaks are broken down into the contributions (flow anomalies) corresponding to all the different time scales involved in the Paraná discharge variability. These "flood anatomies" are based on the results from a previous study where a data-driven signal analysis method was used to fully decompose a 1904-2010 Paraná flow record (monthly means) into several physically meaningful oscillations, with distinctive time scales or periods, and a trend. We show that all the oscillations contributed to the four considered floods, with the only exception of an 18-year cycle that did not contribute to the 1992 flood. The extraordinary large intensity of the 1983 flood resulted mainly from an unusually strong constructive interference between (i) a 3-5-year oscillation related to El Niño events, (ii) a 9-year cycle associated with the North Atlantic Oscillation, (iii) an 18-year oscillation driven by the South Atlantic Convergence Zone, and (iv) a 31-85-year cycle linked to Pacific climate. The contributions of this 31-85-year oscillation to the two greatest floods (1983 and 1992) are larger than the contributions of the secular upward trend, suggesting the importance of this slow oscillation in flood formation processes.