Variabilidade da precipitação em quatro sub-bacias Amazônicas durante o evento ENOS

Abstract

The Amazon Hydrographic Basin plays a fundamental role in the functioning of the climate. However, this region suffers from some extreme episodes (droughts and floods) that affect the condition of the Amazonian climate. However, the greatest climatic anomalies, especially severe droughts, are the result of the occurrence of climatic events, highlighting the El Niño Southern Oscillation (ENOS). In this sense, the objective of the study is to analyze the relationship between the El Niño and La Niña phenomena with the variability of precipitation in the Amazon hydrographic sub-basins. The study covers four sub-basins: Rio Negro, Trombetas, Purus and Madeira. Rainfall data were obtained by the TRMM_3B43 sensor from the Tropical Rainfall Measuring Mission (TRMM) satellite. 264 images were used monthly, from January 1998 to December 2019. The Oceanic Niño Index was obtained from the website of the Center for Climate Studies of the National Oceanic Atmospheric Administration, so that only the years of moderate and strong occurrence of the events were selected. Monthly precipitation images were treated and organized into seasonal averages for all years, thus obtaining seasonal temporary climatological normals for the entire studied region. Only the years in which there was moderate and strong occurrence of climatic events were selected and these were compared with these seasonal averages in order to obtain the positive anomalies (increase in precipitation) and negative (reduction in precipitation) for each year of ENSO. The highest values corresponding to the provisional climatological normals for the rainy season were concentrated in the Purus and Madeira sub-basins. During the dry period, the Rio Negro sub-basin recorded the highest precipitation. El Niño caused negative anomalies mainly in the Negro sub-basins and trumpets. The period with the most intense negative anomalies was 1998/1. During the dry period, the Rio Negro sub-basin suffered the greatest reduction in precipitation. The impacts of La Niña were less significant when compared to El Niño. The greatest positive anomaly of the rainy season was observed in the Negro sub-basin. The dry period showed significant rainfall reductions, resulting from the late effects of the El Niño episodes that preceded it. Seasonally, the rainy season is more sensitive to the effects of El Niño and, although the results of La Niña were not as intense, its positive anomalies were also more present during the rainy season. Extreme rainfall, when associated with a lack of infrastructure, can cause irreparable damage to the riverside population.