Início e fim da estação chuvosa na Monção da América do Sul: análise de tendência e variabilidade da precipitação

Abstract

The precipitation is one of the main meteorological variables, which has a fundamental role on human (social and economic) and environmental development in the world. Given its importance, this study has the main goal to analyze the variability and the trend of precipitation in South American Monsoon System (SAMS) region regarding the aspects at onset and demise of the Rainy Season (Onset and Demise). The dates of Onset and Demise were found through the antisymmetric outgoing longwave radiation (OLR) in relation to the equator (RolAnt) in the 1979-2019 period, being that as regions of analysis were determined with the method of clustering of OLR in the regions of the SAMS and the North America Monsoon System. The application of this technique sought to automate the method previously developed, so that this method became more objective. These regions were defined based on Pearson's correlations and analyzes of the precipitation and OLR annual cycles of the result of the clustering of both monsoon systems. Thus, improvement of the method of detecting Onset and Demise dates through RolAnt reflected the main aspects of the temporal and spatial evolution of SAMS, being as found pentads of Onset and Demise consistent with previous studies in the region. The Mann-Kendall trend test applied to SAMS regions revealed that, in general, there is a reduction in precipitation during the period analysis, which is clearer in the rainiest season from December to February (DJF). In addition, more and less intense events in DJF were identified in the SAMS regions using the quartile technique (third and first, respectively) showing that there is a trend for more (less) intense events to be present at the beginning (end) of the period of study. When the linear trend is removed, events are more evenly distributed over the entire period. For the latter case, compositions of the standardized anomalies Sea Surface Temperature showed standard of El Niño (La Niña) in less (more) intense events in the regions referring to the Amazon Basin, east of the Amazon Basin and Western-Central Brazil. In the eastern region of the Amazon Basin, the anomalously colder (hot) Tropical Atlantic also can influence in cases less (more) intense precipitation events. Therefore, the results found in this work corroborate with a better understanding of the aspects associated with onset and demise in the SAMS region, improvement of the detection method previously developed, being able to contribute to climatic forecasting and monitoring centers in the region.