The probability occurrence of these indexes events during the period 1955-1985 is found to decrease. The end of this period appear then as the most wet in Argentina being the only event in the instrumental period and over the century. Before 1955 and since the beginning of the century, droughts have had a non homogeneous behavior, specially in NEA. So that, while around 1915 this region had a wet period with low probability of droughts, the rest of the country presented high indexes associated with a high probability of drought events.
From the comparison it comes out that the trend of the areal drought index is poorly oscillating in the Humid Pampa, while having important oscillations of middle frequency in the remaining regions.
During the last fifteen years, this drought index has increased gradually, having a stronger upward trend in the NOA and Centro Cuyo, which are the most continental regions of Argentina. Precisely in these regions the annual precipitation decreases gradually since the strong droughts during 1988-1989 and 1995-1996 associated to strong La Niña events.
Concerning the long term behavior of precipitations in Argentina, it is important to highlight that the three regions: NEA, La Pampa west of Buenos Aires, and La Pampa north of Patagonia, have an increasing trend with a decrease in the occurrence probability of drought events. Instead, over Comahue the opposite trend is seen, with an increase of drought events probability.
The long term behavior of droughts in Argentina here analyzed, had a great impact over the regional economies due to agricultural growth over semiarid regions, wet areas becoming arid ones and losses in hydroelectri
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