Períodos úmidos e secos no estado de Alagoas via índice de seca

Abstract

The state of Alagoas has its economic base focused on agriculture, and knowledge of the rainy and dry periods is essential for the success of agricultural enterprises. The objective was to characterize the rainy and dry periods in the state of Alagoas through multivariate analysis applied to the Standardized Precipitation Index (SPI). Initially, monthly rainfall data from 54 stations in the period (1960-2016) were used. These data had gaps that were filled in via the multiple imputation method, filled in and validated, where Sertão (r=0.65; R2=0.42; EPE=54.85 mm; RQEM=54.84 mm), Agreste (r= 0.69; R2=0.47; EPE=70.97 mm; RQEM=70.97 mm) and East (r= 0, 61; R2=0.37; EPE=154.87 mm; RQEM=109.48 mm). Cluster analysis (AA) was applied to time series (definition of homogeneous regions) and SPI-12 (annual) - (determination of dry and rainy periods). The accumulated annual rainfall presented two distinct periods: 1960 to 1990 (P1) and 1990 to 2016 (P2), according to the Pettitt test. Both periods alternate according to the phases of La Niña and Neutral (rainy years) and El Niño (dry years). In terms of monthly rainfall, only the eastern part of Alagoas increased the number of rainy months in the historical series. Of the connection methods tested, the average connection, evaluated through the cophenetic correlation coefficient (CCC = 0.8760) identified homogeneous groups of precipitation, characterizing two regions, one on the coast (G1) and another further inland (G2), and two non-homogeneous groups (NA) in the state. The annual SPI helped to identify dry and wet periods, regardless of the El Niño-Southern Oscillation (ENSO) categorization. The SPI-12 categories show high annual and decadal variability across groups, except as extremely dry and wet. There is greater variability in the dry and rainy periods near the coast than in the interior of the state.