The work aims at briefly explaining the anthropic component of the increase of annual mean flows taking place from 1971 all along the "Río de la Plata" basin.
Comparing the obtained results from the flow series, it could be observed that the discharges in the rivers belonging to the "Río de la Plata" basin was above expectation in the last decades. The flow series mean in the period 1971-1992 is, on average, a 34% higher than the mean in the period 1931-1970.
As regards precipitation, it is not possible to accurately quantify the differences between the rainfall previous to and after 1970. With the scarce available data covering the period 1931-1992, we can arrive to the conclusion that the precipitation mean after 1970, upstream the Paraguay River mouth, is on average a 14% higher than the precipitation mean previous to that year (1931-1970).
In the Paraguay River basin the registered increase is of about 17% in the mentioned periods; while in the Uruguay River basin, the increase is even higher than in the other two regions, reaching a 20% difference as regards the period 1931-1970.
Considering the analysed facts, we could observe evidence of a strong influence of the substitution of coffee plantations for annual cultures taking place mainly after 1970, which coincides with the flow increase; and also in the same period, a precipitation increase undoubtedly producing a flow increase.
The effect of those alterations on the use of the soil could be permanent, but the effect of precipitation could be temporary. Then, the question is: Which is the importance of each effect on the mean discharges?
Anyway, whichever is the answer to that question, it can only affect the results of the present study in a quantitative way but not qualitatively.
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