chapter - Atmospheric and Oceanic Science

the central area of the high basin of the Paraná) happened during El Niño events,
and that none happened during the La Niña phase. Those maximum peaks took
place in Spring 0 (0 indicates the onset year of El Niño event) or in Autumn + (+
indicates the year following the onset of El Niño event). The largest peaks took
place during the Autumn +, when SST anomalies in El Niño 3 persisted until May
+. Also, whenever the anomalies in El Niño 3 persisted until Autumn +, there were
important discharges in the Paraná River. The third remaining part of the maximum
peaks happened during the Spring or the Summer of neutral periods.
In the case of the Uruguay River, Camilloni and Caffera (2003) explain that
its basin is part of a region with a strong precipitation signal during the ENSO warm
phase, when in general, the largest monthly discharges take place, associated most
of the times to extreme daily peaks. They establish that the most intense anomalies
in monthly discharges happen mostly during El Niño's warm phases that seem to
induce extensive positive rainfall anomalies in the region.
Barros el al. (2004) show that two third of the maximum peaks of the
Paraguay River in Asunción occur during the ENSO warm phase, and that El Niño's
signal is particularly clear for the peaks that happen during Autumn +. The third
remaining part of the maximum peaks happens indistinctly during La Niña or neutral
phases. In these cases an average consistent meteorological pattern in the south
Pacific is observed from April until August that, eventually, would allow a precipitation
forecast.
References
Hydrological trends
Barros, V., L. Chamorro, G. Coronel and J. Baez 2004: The major discharge events in the
Paraguay River: Magnitudes, source regions, and climate forcings. J Hydrometeorology
2004 Vol 5, 1061-1070
Camilloni, I.A. and V. R. Barros 2003: Extreme discharge events in the Paraná River and their
climate forcing. J. of Hydrology, 278, 94-106.
______ and R. M. Caffera 2003: The largest floods in the Uruguay river and their climate forcing,
enviado al J. of Hydrometeor.
García, N. and W. Vargas 1998: The temporal climatic variability en the Río de la Plata basin displayed
by the river discharges, Climate Change, 38, 359-379.
Jaime, P. and A. N. Menéndez 2002: Análisis del Régimen Hidrológico de los Ríos Paraná y
Uruguay, Informe INA-LHA 05-216-02, Comitente: Proyecto Freplata.
Subsecretaría de Recursos Hídricos-Argentina. WWWeb.
www.mecon.gov.ar/hidricos/mapashidiricos/mapageneral.htm
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