Influencia de ENOS sobre las variaciones interanuales de ciertos ríos en América del Sur

The response of South American rivers to ENSO stimuli is studied under three conditions: El Niño (EN), Anti-Niño (AN), and normal years. A regionalization is thus obtained. Rivers in coastal Peru, Ecuador and extreme south of coastal Colombia have high discharges during summers with El Niño. Low run-off is experienced in Anti-Niños. Rivers in the Sierra of Peru and the Altiplano react with low discharges to EN, while discharges are normal under the two other conditions. Rivers of Central Chile and Andean Argentina have high run-off during EN and low run-off during AN. Rivers in Patagonia and southern Chile show an independence from the phases of ENSO since their high discharges occur in normal years. Rivers of the Pampa, the Rio de la Plata lowlands, and the southern tip of Brazil have high discharges during EN and low run-off during AN. Rivers of central Brazil display independence from the three conditions. Rivers of north-east Brazil have extremely low run-off during EN and experience high waters during AN. The rivers of the vast Amazon basin have differentiated responses. Rivers in the central part of the basin display low discharges during most EN and high waters during AN. However, rivers that originate in the eastern slopes of the Andes tend to rise during special EN events. Rivers of the Guianas, coastal Venezuela, and the Caribbean tier of Colombia experience low run-off during EN and high discharges during AN. In the Andes of Ecuador and southern Colombia a mixture exists: some of them peak during extreme EN, others during AN. This region seems to be the best example of the mixed stimuli which concern the central Andes, opening on to the equatorial Pacific, the Amazon basin, and the areas of South America opening on to Atlantic and Caribbean influences.