Dry Spells, Wet Spells and Rainfall Persistency at São Gonçalo (NE Brazil)

Abstract

Results of a study of dry spells, wet spells and rainfall persistency at São Gonçalo, a semi-arid station in Northeast Brazil are presented in this paper. Daily rainfall data for a period of 40 years is used in the study. Frequency distribution of dry spells of different durations at the station is compared with those derived from two statistical models. It is found that the Eggenberger-Polya model provides better results than the logarithmic model. Rainfall persistency is investigated using Erickson’s (1965) and Jorgensen’s (1949) models. The incidence of wet spells lasting one, two and three days is less than expected on chance and spells lasting longer than three days are more frequent than expected on chance basis. Rainfall persistency reaches a maximum value on the third day of a rainy spell. Key words: Rainfall, persistency, dry spells, wet spells, probability of rain.