Statistical Analysis of Dry and Rainy Event of Maranhão Rainfall

Abstract The state of Maranhão is located in a transition zone between the northeastern semi-arid region, the hot and humid Amazon region and the central Brazilian plains. It presents well defined climatic conditions, with normally dry winter and predominant rains in autumn and summer. Considering the importance of detecting and specifying rainfall anomalies in the State, the present study used multivariate analysis techniques to find spatial and temporal patterns of SPI-6, and to quantify extreme dry and rainy events according to their frequency and period for the years of 1987 to 2015. The results showed that by the semester scale of SPI, the state is divided into five homogeneous regions, and that the mode of variability of SPI-6 explains well the rainfall regime, emphasizing that the state has two well-defined rainfall seasons. The results also showed that the highest incidences of drought events occurred in the south and the highest rains were recorded in the north of the state of Maranhão. Most cases of extreme dry/rainy events occurred in El Niño/La Niña years, especially in the Northern region.