Effects of extreme phases of El Niño–Southern Oscillation on rainfall extremes in Alagoas, Brazil

Abstract

AbstractThe Northeast of Brazil (NEB) is influenced by the phases of El Niño–Southern Oscillation (ENSO), which are associated with increased or decreased rainfall in the East NEB (ENEB). The study evaluated the effects of extreme ENSO phases on rainfall extremes in ENEB. Rainfall data from 54 stations in Alagoas were obtained from the National Water and Basic Sanitation Agency (ANA) and subjected to statistical analysis, with a data imputation method used to fill in gaps in the time series. The Inverse Distance Weighting (IDW) method was consistent and suitable for spatially representing rainfall data in the state of Alagoas, according to the adopted statistical indicators. Extreme, decadal and anomaly maps were interpolated using IDW method in Quantum GIS (QGIS), due to the positioning of the stations. The criteria for analysing extreme ENSO years were based on the Oceanic Niño Index (ONI) for region 3.4, between 1960 and 2016. The results show high interannual variability due to ENSO phases in the climatic mesoregions of Alagoas. In over 70% of extreme ENSO years, rainfall was below average (during strong and very strong El Niño) or above average (during strong La Niña). Some cities in the mesoregions of Alagoas experienced higher rainfall than others, even in extreme ENSO situations, suggesting the influence of physiography and multiscale meteorological systems. On a decadal scale, the East region recorded the highest rainfall accumulations, primarily due to decadal variability of two rainfall cores, corresponding to the Metropolitan Region of Maceió (MRM) and the northern part of the state. An exception is the Upper São Francisco region, which experiences dry decades. The East mesoregion (coast) had higher rainfall records compared to the more continental mesoregions (Hinterland and Arid), regardless of ENSO phases and interannual and decadal scales.