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Drought is the most complex natural hazard that can occur over large spatial scales and during long time periods. It affects more people than any other natural hazard, particularly in areas with a dry climate, such as the semiarid region of the Brazilian Northeast (NEB), which is the world's most populated dry area. In this work, we analyzed trends and the spatial distribution of drought characteristics (frequency, affected area, and intensity) based on the Standardized Precipitation Index (SPI) on annual (SPI-12) and seasonal (SPI-3) scales. The study used monthly precipitation data recorded between 1962 and 2012 at 133 meteorological stations in Pernambuco State, Brazil, which is located in the eastern part of the NEB and has more than 80% of its territory characterized by a semiarid climate. The regions of Sertão, Agreste, and Zona da Mata of Pernambuco were considered for comparison. The Mann–Kendall and Sen's slope tests were used to detect the trend and determine its magnitude, respectively. The results indicated that annual droughts in the state of Pernambuco became more frequent from the 1990s onwards, with summer having the greatest spatial coverage, followed by winter, autumn, and spring. Sertão presented a greater number of stations with a significant positive trend in drought frequency. Regarding the drought-affected area, global events occurred in a greater number of years on an annual scale and during the summer. Trend analysis pointed to an increase in areas with drought events on both scales. As for the drought intensity, the entire state of Pernambuco experienced drought events with high intensity during the autumn. The relationship between drought characteristics indicated an increase in the affected area as the result of an increase in drought intensity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]