FEDERAL UNIVERSITY OF TECHNOLOGY AKURE
Title :
THE IMPACT OF EL NINO/SOUTHERN
OSCILLATION ON RAINFALL
CHARACTERISTICS IN FIVE CLIMATIC ZONES
OF NIGERIA
Author:
Supervisor:
DARAMOLA ALEX OLASUNBO
Prof. K. O. Ogunjobi
Department: METEOROLOGY
School:
SEMS
Year:
JUNE, 2015
ABSTRACT
This research work is aimed at investigating the impact of El Nino/Southern Oscillation (ENSO)
on Rainfall Characteristics at five climatic zones of Nigeria. The study specifically investigated
the precipitation index for ENSO and Non ENSO years at each station; estimated the onset and
cessation dates of rainfall for each of the stations; and compared the impact of ENSO and La
Nina on rainfall characteristics which include Rainfall amount, Onset date, Cessation date, Rainy
days, Dry days, August rainy days, August dry days and August amount across the stations. The
Precipitation index (PI) was calculated for all the years and the Nature of Dry and Wet years
were identified during El Niño, La Niña and normal years. Percentage cumulative mean rainfall
method was used to estimate the onset and cessation date of rainfall at each of the stations. The
long-term mean for each of the characteristics was calculated and compared with the yearly data
for each of the selected stations. Cramer’s test was used to determine if there is any difference
between the means of ENSO, La Nina and normal years. Results were compared between the
ENSO years, La Nina years and normal years over a period of 30 years (1982 - 2011). Generally
for all the stations, ENSO years annual rainfall amount is lower than the long term mean, onset is
later and cessation of the rainy season is earlier than the normal years. Duration is shorter during
ENSO years than other years and rainfall amount in August is lower in ENSO years.
Precipitation index for all the stations shows that there are more droughts during ENSO years
when compared with Normal years. It was shown that the effects of ENSO was felt more in
Nguru (Sahel), Yola (Sudan-Sahel), and Minna (Guinea-Sudan), while, lesser effect of ENSO on
rainfall characteristics was felt in Ibadan (Wooded savannah) and Calabar (Forest belt). For La
Nina years which are direct opposite of ENSO years, across all the stations, annual rainfall
amount is higher than the long term mean, onset is earlier and cessation of the rainy season is
later than the normal years. Duration of the raining season is longer and rainfall amount in
August is higher than the long term mean. Precipitation index for all the stations shows that there
are no droughts during La Nina years. Since there are some teleconnections between ENSO and
rainfall at the five climatic zones of Nigeria, it would be possible to predict extreme rainfall
events like drought if the periodicity of ENSO can be understood.