Análise da precipitação pluvial da pré-estação e da estação chuvosa do Estado da Bahia.

Abstract

The objective of the present research was to investigate the interannual and intraseasonal variability of the beginning/end of the wet pre-season and wet season of the homogeneous precipitation regions of the state of Bahia and the causes of this variability. For this purpose, Ward's minimum variance clustering method was applied to the climatological averages of precipitation of four hundred and ninety points. The concept of contiguous areas was used so that each homogeneous region of precipitation was composed of a single area. Six homogeneous regions were obtained, however, after an analysis of the beginning and end of the wet and pre-season periods, it was observed that, for the purpose of this study, regions five and six were composed in a single region. When analyzing the ten-year precipitation climatology of the five homogeneous regions, it was found that region 2, which represents the areas with the lowest precipitation in Bahia, and region 3, characterized by monsoon precipitation, did not present a pre-rainy season. However, when performing the analysis year by year, of the 34 years analyzed, in eight years there was wet pre-season occurrence in region 2, and in region 3, in fourteen years there was pre-rainy season. In region 1, during the rainy season, there was a decrease in precipitation in the years of El Niño, La Niña and meridional gradient of sea surface temperature anomaly in the Tropical Atlantic (meridional gradient and SST anomaly) negative, while in the In neutral years and with a positive SST meridional gradient, there was an increase in precipitation. In region 2, an increase in precipitation was observed during the rainy season of La Niña years. In region 3, there was an increase in precipitation in the La Niña years and a positive SST anomaly meridional gradient. The precipitations during the rainy season of region 4 did not present statistically significant differences for the years of El Niño, La Niña, positive and negative SST anomaly gradients and neutral. Meanwhile, in region 5/6 there was an increase in precipitation during the rainy season in the years of La Niña and meridional gradient of negative TMS anomaly. This configuration is similar to what occurs in the north of the Northeast. It was found that in the period from September 1979 to August 2013, during the episodes of the three strongest El Niño events, which occurred in the years 1982/83, 1992/93 and 1997/98, in general, no presence of wet pre-season and wet season in all five homogeneous precipitation regions of Bahia. In general, the wet pre-season starts with MJO in phase 7 and ends with MJO in phases 2, 3 and 4.