Southern Brazil rainfall variability

Abstract

Seasonal and annual rainfall fluctuations were studied in the Brazilian states of São Paulo, Paraná, Santa Catarina and Rio Grande do Sul, using DNAEE (Departamento Nacional de Águas e Energia Elétrica) e DAEE (Departamento de Águas e Energia Elétrica) data, from 1960 to 1991. The aims were to establish a precipitation seasonal scale model in each State and to understand its variability during wet and dry periods, through different statistical (descriptions) methods. The deterministic processes were filtered as, for instance, the highly pronounced annual cycle. Spectral analysis was used to obtain new series in which unknown processes were shown. The studied precipitation got maximum values in the wet period and minimum values in the dry period in São Paulo, coastal and northeastern Paraná and Santa Catarina coast. In the continentals Paraná and Santa Catarina, and in all Rio Grande do Sul, the precipitation structure was homogeneous. The variability after filtering showed that the series were essentially dominated by randon processes. Persistence, when present, is given by annual wave.