The characterization of rainfall patterns is fundamental for deciding farming practices both for the high production and low production periods, in Formoso do Araguaia, State of Tocantins, Brazil. Daily rainfall data were obtained in the period 1981-1997, excluding the years 1991, 1992 and 1993, totaling 14 years of observation. These data have been analyzed using the ANFLPLUVIE.EXE and Chuva systems (Assad et. al. 1994). The yearly and monthly rainfall means were analyzed; with a frequency in time intervals of 30, 15 and 10 days with a probability of occurrence of 20, 50, and 80%, and so the frequency of dry days as well. The mean annual rainfall was 1,675.7 mm; the highest monthly mean rainfall occurring in December (330.0mm) and the lowest in April (109.3mm). Most of the rain in the region (95.16%) occurred from October to December. In 85.71% of the observed years-annual rainfall value were above 1,000 mm.
precipitation; dry days