The study exposes the rainfall descriptors observed in the Cachi river basin, during 1991 to 2008, due to the nature of its development, it is quantitative descriptive, not experimental, longitudinal, acted on a chronological series of 3016 records of monthly precipitation in 22 hydrometeorological stations managed by the Regional Government of Ayacucho. The data were organized in Excel and processed in SPSS, then the analysis of variance was performed, applying descriptive statistics and multiple comparisons of Duncan, observing that at least one of the averages of the monthly rainfall is different from the others. The results revealed that, from 1991 to 1999, the average monthly rainfall in the basin showed small cyclical variations that denotes fluctuation from a very low level to a slightly high level, except for the year 1993 with an accentuated precipitation at a high level. In the...