Analysis of rainfall seasonality in Pernambuco, Brazil

The main objective of this paper is to analyze the rainfall regimes of Pernambuco, a northeastern Brazilian state, based on the seasonality indices (the individual, SI_i , and the general, SI ) and the replicability index, RI . These indices were derived from monthly rainfall data, recorded between 1953 and 2012, at 125 weather stations. The modified Mann–Kendall test and Sen’s slope estimator were applied to investigate trends in the SI_i time series. A regression analysis of SI_i , SI , and RI with the geographical longitude produced a statistically significant linear correlation. The calculated SI index indicates that the mean rainfall regime of the coastal area (Zona da Mata) and the central area (Agreste) of the state can be classified as rather seasonal with a short drier season. The western part (Sertão), in turn, exhibited mean rainfall regime between seasonal and markedly seasonal with a long drier season. Concerning the replicability index, results suggest that Agreste is the region with the least replicable rainfall regime in the state. The analysis of the two 30-year sub-periods shows significant changes in the mean values of SI_i indicating the shift in rainfall regime toward extreme seasonality with prolonged dry season in the Sertão region and toward more regular with shorter dry periods in Zona da Mata and Agreste region.