Research on rainfall and annual daily maximum discharge rates is essential to support decisions during the design of hydraulic structures. This study tested the adequacy of probability functions to predict the probable rainfall and discharge rates of the Aiuruoca River Basin in Minas Gerais State in Brazil. This basin is very important as starting point of the Rio Grande Basin that eventually discharges into the Parana River in the southern region of Brazil at the border with Argentina. It was found that the log-normal two parameters probability function provided the best fit to historical monthly rainfall series. For example, in the month of January, there is a 75% probability that 201 mm of rainfall will occur. This is the month with the highest volume of rainfall in the region. On another hand, for flow rate, the best fit was provided by the log-normal distribution with three parameters.
probability distribution; Log-Normal; Gamma distribution; water resources planning