Prediction of Droughts in North-East Brazil: Role of ENSO and Use of Periodicities

The relationship between El Niño and droughts in north-east Brazil is poor. From 46 El Niño events (strong and moderate) during 1849–1992, only 21 (ca. 46 per cent) were associated with droughts at Fortaleza, Ceara (north-east Brazil) and only 26 (ca. 57 per cent) with negative deviations (of any size). Thus, forecasts of droughts based on the appearance of El Niño alone would be wrong half the time. Instead, predictions based on significant periodicities (ca. 13 and ca. 26 years) give reasonably good results. Data up to 1978 could predict the drought that occurred during 1979– 1983, although the severe drought of 1983 was attributed to a strong El Niño. Mild droughts during 1991–1993 were also foreseen. In future, severe droughts are predicted for 2000–2010 in north-east Brazil. However, the prediction skill is not very good and predictions should be checked by analysis of as much updated data as possible. Predictions beyond about 5 10 years are not reliable. The significant periodicities in North-east Brazil rainfall series might be related to periodicities in Atlantic parameters (Sea-surface temperatures, etc.) that are well correlated with north-east Brazil rainfall. © 1997 by the Royal Metrological Society.