MONTHLY RAINFALL DISTRIBUTION IN GOIÁS AND THE FEDERAL DISTRICT: A CASE STUDY OF AN EL NIÑO EVENT

Abstract

ENSO and PDO are phenomena that modify atmospheric circulation over the equatorial/tropical Pacific Ocean and lead to climate changes in various parts of the world. This study aimed to analyze the distribution of monthly rainfall totals during the rainy season months in Goiás and the Federal District during two El Niño episodes—one associated with the warm phase of the PDO and the other with the cold phase. To achieve this objective, historical rainfall data from 1975 to 2016 were used, obtained from 40 rain gauge stations maintained by the National Water Agency (ANA) and the National Institute of Meteorology (INMET). El Niño events and the positive and negative phases of the PDO were identified using NOAA data. Two extreme El Niño episodes classified as very strong were selected: one during the warm phase (1982/1983) and the other during the cold phase (2015/2016). The data were organized into a database, and statistical techniques were applied to delineate rainfall regions within the study area, as well as to determine maximum and minimum limits. Additionally, F-tests and Student’s t-tests were performed to compare the monthly totals recorded during the two episodes and to assess whether significant differences existed. The Standardized Precipitation Index (SPI) was also applied for each month analyzed to identify rainfall anomalies. The results showed that the PDO phases influenced the monthly distribution of El Niño episodes. During the warm phase, El Niño was intensified, and positive anomalies in the monthly rainfall totals were recorded in the analyzed months.