Análise da utilização do indice ONI 3.4 na previsibilidade de chuvas no Nordeste do Brasil

Abstract

In this work, the oceanic index Niño 3.4 (ONI) was used, for the period from 1980 to 2020, with the main objective of evaluating the relationship of the positive, neutral and negative phase intervals of the ONI and its influence on the rainfall variability in the northeast of the Brazil. For this, precipitation data (P) from the University of Delaware (UDEL) was used. The Northeast of Brazil (NEB) was segmented into three regions of interest, “East”, “Center-South” and “North”. Was chosen this cut because of the specific conditions of the systems that predominantly cause rainfall at different times. ONI is built in quarters, where the current month is used with the next two months starting in December. P anomalies were performed with ONI positive, negative and neutral to determine the positive or negative anomalies of P. Furthermore, correlations were performed between ONI and Niño 3.4 for the quarters FMA, MAM, AMJ, MJJ, JJA, OND and finally NDJ, with the Niño index simultaneously and the Niño index leading and one, two and three quarters. Seeking to observe patterns that may contribute to rainfall forecasts in the region, it was observed that, in general, when La Ninã occurs, precipitation anomalies (P) above average can be expected in the northern and eastern parts of the NEB. However, if La Niña occurs in the NDJ quarter the precipitation in much of the NEB tends to be around and/or below average and if El Niño occurs, around and/or above average. The correlations between Niño 3.4 and UDEL precipitation proved to be good, that is, correlations that generally ranged around 0.4, presenting a level of statistical significance of the correlations above 95% in most of the analyzes carried out in the NEB, with both the simultaneous index and the lead index in one, two or three quarters, which means that Niño 3.4 is a good predictor for rains one to three quarters in advance in most quarters studied, mainly in the quarters at the beginning of the year (February, March and April – FMA, for example).