Resumen
The Paraná river is the most important component of the La Plata basin, sustaining regional economies in three countries. In the last decades, significant regional changes such as deforestation and crop substitution have been taken place in the Paraná basin. This fact could have modified the basin response in terms of the Paraná streamflow. The main objective of this paper is to analyze the structure of the evapotranspiration (ET(t)) time series of the upper Paraná basin. We analyzed the relationship between the variables in the water balance equation, then we applied a singular spectral analysis (SSA) to learn more about the temporal structure of the ET(t) time series. The correlation study shows that ET(t) is correlated with precipitations in the northern sub-basins but it is not correlated at all in the southern basin. The time structure of ET(t)1, ET(t)3 and ET(t)4 exhibit low-frequency signals while the ENSO-range signals are statistically significant in ET(t)1 and ET(t)4 although it also appears in ET(t)2 and ET(t)3 as a weak signals. Looking at the whole basin, ET(t) would be affected either by changes in the basin physical properties or by the ENSO-range signals present in precipitation..