A regionalization method based on precipitation analysis proposed here is applied to the monthly precipitation data of 175 localities in Ceará State. It resulted in the identification of three homogeneous precipitation groups. Group 1 being predominantly semi-arid. Such groups were compared with the seven climatic regions recognized by 'Fundação Cearense de Meteorologia e Recursos Hídricos' (FUNCEME) and it was found that the method is capable of identifying the Ibiapaba and Cariri regions, as well as the area formed by the East Central and West Central regions and the area formed by the coastal regions of North and South. The rainy season for all the localities of the Ceará State was identified utilizing Frère & Popov (1979) method. It was found that in 143 (81.71%) of the 175 localities, the rainy season occurs from January to May and in 69 (65.71%) of the 105 localities of Group1, the rainy season occurs from February to May. Finally, the daily precipitation data were used to verify the probability of occurrence of the dry spells in each of the three ten-day periods (days 1 to 10, 11 to 20 and 21 to the last day of the month) for the months of January to June and for all the 105 locations of the Group 1. It was observed that the mean probability of having a dry spell in the first, second and third 10 day-periods of the month of January is 51, 39 and 25%, respectively; in February it is 20, 18 and 21%; in March 10, 7 and 6%; in April 9, 10 and 11%; in May 25, 25 and 28%; and in June 38, 43 and 51%.
homogeneous groups; regionalization; rainfall; semi-arid
