EFFECT OF SEA SURFACE TEMPERATURE AND ENSO INDICES ON RAINFALL REGIME OVER NIGERIA

Abstract

This study investigates the effects of Sea Surface Temperature (SST) over South Atlantic Ocean and EI Nino/Southern Oscillation (ENSO) on rainfall in some selected stations in Nigeria. The study also determines the response time of rainfall occurrence between SST’s for South Atlantic Ocean and Nino 3.4 indices. Monthly rainfall, surface air temperature and uv wind data from some selected meteorological stations in Nigeria from 1975 to 2004 were analysed, in relation to sea surface temperatures (SSTs) from ENSO region of the tropical Pacific Ocean (Nino 3.4 (170oW-120oW, 5oS-5oN)) and Atlantic Ocean (longitude 0oE-8o.20’E and latitude 1oN-3o.50’N). The results show that an increase or decrease in SST and Nino 3.4 is accompanied by a corresponding change in temperature over Nigeria; however there is a better agreement with the South Atlantic Ocean SST compared to the Nino 3.4 SST. The analyses have shed some light on understanding the variability of SST anomalies observed for this period. Variations in SST anomaly within the study areas show that for South Atlantic Ocean, 1987,1988, 1998 and 2003 were severe years of high ENSO while Nino 3.4 of 1977, 1982, 1983, 1987, 1991, 1992, 1997,1998 and 2002 were also severe years. This indicates a very high variation in SST anomaly during the period of the study. The year 1987, 1988, 1997and 1998 with high variation in SST anomaly were notable EI-Nino years with a positive rainfall anomaly in some stations which suggest an increase in rainfall amount in those years. The response time or correlative time proximity which the South Atlantic Ocean SST impacted on rainfall was about three months within the coastal region. But for hinterlands, it goes between four to five months on an average.