Comportamento estatístico de séries temporais de pluviometria no Nordeste do Brasil.

Abstract

The annual precipitation totals, referring to the hydrological years from 1911 to 1984, of 89 rainfall stations in the Northeast of Brazil were analyzed. The Harmonic analysis of the precipitation series showed characteristic cycles around 74, 26, 13, 3-4 and 2-3 years. In only two locations (Fortaleza and Catolé do Rocha), the 13 and 26 year cycles are simultaneously significant, at a level of 5%, according to Fisher's thesis. The Southern Oscillation Index (IOS) was correlated (from years of strong or moderate El Nino occurrence to rainfall deviation from 1935 to 1984). Fisher's and Student's tests were used to To determine, respectively, the significance levels of the precipitation series associated with the contribution of each harmonic to the variance and the correlation coefficient between IOS and precipitation deviations. Based on Fisher's test, the 13-year cycle is more closely related to the northern Northeast, while the 26-year cycle is present in the rainfall of the east coast of the Northeast (south of the latitude of 9 ° S) and in central regions of the State of Bahia. On the other hand, the Student test indicated that the relationship between El Nino and Northeast droughts are strongest in the latitude range of 4.5 ° S to 14.5 ° S, decreasing in the North direction, where rainfall north of the latitude of 4.5 ° Se is influenced by the Intertropical Convergence Zone , and south of this latitude range with a greater influence of the entry of fronts from the south of the country. Among the 89 stations analyzed, only 26 have significant cycles at a level of 10%, according to Fisher's test. For these stations, the sinusoidal model cannot explain more than 50% of the variance of the original data. In general, waste from Northeast precipitation better fit the Normal Distribution. Such residues behave like white noise.