On the prediction of rainfall onset and retreat dates in Nigeria

Summary

This study examined the rainfall onset and retreat dates between 1962 and 1996 in Nigeria, and generated models for their prediction. The study used the composite of rainfall-promoting factors namely, sea surface temperature of the tropical Atlantic Ocean, land/sea thermal contrast between some selected locations in Nigeria and the tropical Atlantic Ocean, surface location of the Inter-tropical Discontinuity and the land surface temperature in the selected locations in Nigeria. Rainfall and temperature data were collected from Ikeja, Benin, Ibadan, Ilorin, Kaduna and Kano, in Nigeria. Cumulative percentage mean rainfall was employed to generate the rainfall onset and retreat dates series, while the method of stepwise multiple regression analysis was used to construct the required prediction models.

The results obtained showed that the hypothesized rainfall-promoting factors are efficient in predicting rainfall onset and retreat dates in Nigeria. The correlation coefficients (R²) obtained are in most cases (>75%) higher than 0.50 (with several of them approaching 0.90). Sea surface temperature and land/sea thermal contrast are the most significant predictor variables. The results also indicated that all the areas of the tropical Atlantic Ocean, from the Gulf of Guinea, through St Helena and Ascension Island, up to the Benguela Current region, influence the inter-annual variability in the rainfall onset and retreat dates of Nigeria.