The spatial-temporal characteristics of annual series of groundwater levels have been studied in a great region of the Argentinean plains, by means of several techniques of temporary and spectral analysis with the purpose of detecting fluctuations, changes of trends and oscillation modes.

These characteristics provide valuable information for the evaluation of the climatic evolution, and the detection of variations in this evolution, either for natural mechanisms or by antropogenic impact, that suggests a climatic change.

A positive trend exists in the whole analyzed region. The spectral analysis presents significant periodicities between 3.4 and 7.5 years, that they show a possible linking with the ENSO phenomenon.

The used methodology responds to a hypothetical conception of the temporary series like that of a signal formed by aleatory components, with characteristics of white noise.

This extensive region shows a spatial-temporal similar behavior. The periodicities linked with ENSO are always present and the structures of the series are similar for the differents periods analyzed.