Análise da variabilidade de secas no estado de Alagoas no período 1936-2019 utilizando o índice de precipitação padronizada e a transformada contínua em ondaleta

Abstract

This work analyzed the variability of droughts in the State of Alagoas in the period 1936–2019, using the Standardized Precipitation Index (SPI) and the Continuous Wavelet Transform. Also was sought to investigate the relationship between the occurrence of droughts and the regime of climatic teleconnections. For this purpose, daily precipitation data were collected from pluviometric stations distributed in 17 cities throughout the region of Alagoas. After filling in data gaps, it was decided to perform a regional weighting using the Thiessen method in order to reduce the amount of data, thus resulting in a time series for each of the five subregions for which the region of study was divided, being: Sertão, Agreste and Lower S. F., Central, Metropolitan, and North. From this, SPI values were calculated for the time scales of 3, 12, and 24 months (SPI-3, SPI-12, and SPI-24, respectively) for each of the subregions. Finally, using the SPIs time series, images of global wavelet spectra were obtained. Considering the SPIs time series, it was found that, in general, droughts presented multi-annual persistence. Mild and moderate droughts were predominant in SPI-3, while only mild droughts showed predominance for SPI-12 and SPI-24. Regarding the images of the wavelet spectra of the SPI time series, it was found that the extreme drought event cycles are better distributed in the Sertão and Agreste and Lower S. F. subregions, while the Central, Metropolitan and North subregions concentrate significant drought events in the period 1978–2019. Finally, it was found that extreme drought events are strongly related to the atmosphere-ocean dynamics of global climatic phenomena in such a way that the drought episodes that affected the whole region of Alagoas occurred in response to the extreme El Niño events. Drought episodes have intensified in situations where the Madden–Julian Oscillation and El Niño occur together. It was also observed that there was a decrease in the frequency of occurrence of extreme drought events as a result of the cold phase of the Pacific (inter) Decadal Oscillation.