The Influence of ENSO in the Flows of the Upper Paraná River of South America over the Past 100 Years

Abstract

Abstract The Upper Parana River is the main tributary of the La Plata River basin, the second largest in South America, contributing with an annual mean flow of 12 000 m3 s−1 to more than one-half of the total water flowing in the La Plata River system. The Parana River has a relevant importance in the region for transportation and hydroelectricity generation. This paper studies the influence of ENSO on the monthly flows measured at Posadas (27°23′S, 55°53′W) during the period of 1901–97. The original data are converted into standardized monthly anomalies, and the annual cycle is removed. Two data subsets are generated: a first group includes the years of warm ENSO events, or El Nino, and the second group includes the years of cold ENSO events, or La Nina. The elements of the subsets are composites of 24 consecutive months starting in January of the year when the ENSO event begins and ending in December of the following year. The results show that the averaged flows observed during El Nino events are alwa...