Homogeneity Analysis of Rainfall Series to Determine the Drought Index (SPI) in the State of Alagoas

ABSTRACT

The objective of this study was to evaluate the rainfall data series, regarding homogeneity, in the calculation of the Standardized Precipitation Index (SPI) and its relation with the events of El Niño - Southern Oscillation (ENSO) for the physiographic regions of the State of Alagoas. To this end, monthly rainfall series were evaluated. These data is used in the SPI determination obtained at the Hydrometeorological Network of the Northeast Development Superintendence stations, available in the databases from the Food and Agriculture Organization (FAOClim Net) and the National Water Agency. Two criteria for series selection were adopted in the evaluation: i) series greater than or equal to 20 years; and ii) beginning and end of series from 1960 to 1990. Based on these criteria, 36 stations in the State of Alagoas, distributed in the physiographic regions of “Zona da Mata”, “Litoral”, “Sertao”, “Sertao do Sao Francisco”, “Baixo Sao Francisco” and “Agreste” were selected. Gap filling by linear regression was performed in the selected series and the accumulated waste method was applied for homogeneity analysis. PPI was determined for the homogenized and non-homogenized series and it was later used to characterize drought severity in the physiographic regions. Strong ENSO events together with IPP homogeneity define more realistic standards for wet and dry periods in the region when compared to moderate ENSO events associated with non-homogenized IPP.

Keywords:
ENSO; drought index (SPI); data processing.