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Web End = Meteorol Atmos Phys (2017) 129:157171 DOI 10.1007/s00703-016-0461-1
http://crossmark.crossref.org/dialog/?doi=10.1007/s00703-016-0461-1&domain=pdf
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Rainfall variability over Alagoas under the inuences of SST anomalies
G. B. Lyra1 J. F. Oliveira-Jnior1 G. Gois1 G. Cunha-Zeri2 M. Zeri2
Received: 22 September 2015 / Accepted: 13 May 2016 / Published online: 21 May 2016 Springer-Verlag Wien 2016
Abstract The rainfall variability for the state of Alagoas, Northeast of Brazil, was evaluated based on the Standardized Precipitation Index (SPI). Harmonic decomposition was applied to 31 years-long (19601990) series of SPI, from 33 stations, to relate their modes of variability to El Nio-Southern Oscillation (ENSO) and the Atlantic Ocean sea surface temperature (SST). The most important harmonics identied by the spectral analysis had periods of 1015 and 23 years, followed by other oscillations with smaller periods. The 1015 years harmonic was associated with the Atlantic interhemispheric SST gradient (AITG), a cross-equatorial dipole which impacts the northeast region of Brazil by inuencing the position of the intertropical convergence zone (ITCZ), leading to dry or wet conditions. The 23 years harmonic was consistent with the variability
of ENSO events. The harmonic analysis is a powerful tool to identify the principal modes of variability of SPI. Although the magnitude of SPI is underestimated in some cases, this tool signicantly increases the knowledge of the main drivers of rainfall and droughts in the region.
1 Introduction
Alagoas is one of the poorest states in Brazil, and its Human Development Index (HDI) is the countrs worst since 2000 (Malik 2013). The economy has been heavily based on the primary sector (agricultural and livestock) and the most important industry of Alagoas is processing of sugarcane, for sugar and ethanol (IBGE 2006). Considering that yields rely on the climate conditions, the characterization and trends of droughts, intense rainfalls or any other extreme climatic event is very important for both the economy and society development.
Alagoas state is located in the northeastern Brazil region (NEB), which is historically characterized by extreme climatic events, such as the drought from 1777 to 1779, when thousands died in the state of Cear (Duarte 2001). One century later, the three eights drought of 1888 affected the same region leading to crop failure, cattle perishing, starvation and emigration (Gonalves 2000)....