Assessment of the Teleconnection Between El Nino Southern Oscillation (ENSO) and West African Rainfall

Abstract

In this study, rainfall variability over Nigeria was analysed in relation to ocean-atmospheric interaction due to ENSO event. Monthly rainfall data were collected from Nigerian Meteorological Agency (NIMET) from six (6) synoptic stations selected across three (3) geographical regions in Nigeria for a period of 26 years (1988 - 2013). Cluster analysis grouped the rainfall data into three clusters namely Coastal South, Middle belt and Sahel North, while Southern Oscillation Index (SOI) data from 1988 to 2013 was retrieved from National Ocean Atmospheric Administration (NOAA) as updated by the National Centre for Environmental Prediction (NCEP). Rainfall Analysis Index (RAI) was computed for each of the three sub-regions and respective anomalies revealed in a time series. Additionally, linear correlation analysis between the RAI and SOI were computed at lag three months to determine any relationship between ENSO and Nigerian rainfall. The result shows that correlation between RAI and SOI were not uniformly significant, with Region 1 having a positive correlation and a negative correlation recorded for regions 2 and 3. Likewise, simple matrix confirm for region 1 the positive rainfall anomalies occurring during warm ENSO phase. How forecast will be improved if ENSO indices are included as precursor variables in rainfall forecast for the region will be of interest.

Key Words: El Nino Southern Oscillation, Nigerian rainfall, Southern Oscillation Index (SOI)