North Atlantic Oscillation and Rainfall Variability in Southeastern Nigeria: A Statistical Analysis of 30 Year Period

Abstract

This study analyzed rainfall variability in Southeast region of Nigeria using graphical models, as well as using statistical approach to investigate any significant relationship between the global North Atlantic Oscillation (NAO) Index and the regional rainfall variability in region. The study was conducted in three States of Southeastern Nigeria namely, Abia, Ebonyi and Imo States that lie between Latitudes 40 40’ and 80 50’N and Longitudes 60 20’ and 80 50’E. Data for the study included 30 years (1988 - 2017) archival time-series monthly rainfall values for the three study States, acquired from Nigerian Meteorological Agency (NIMET), offices in the states, and Standardized values of NAOI (North Atlantic Oscillation Index) for the same period, which were collected from a website, on the NOAA Data Center, USA. In the data analyses, the first method was adopted by using graphs to illustrate mean annual rainfall values for thirty years. Coefficient of variability was employed in evaluating the degree of variability of values from the mean rate. The second analysis was accomplished using correlation models to ascertain any relationship between NAOI and rainfall in Southeast Nigeria. The results showed a significant variability of rainfall in the region from January to December (mean monthly) within the study period. A negative correlation value of 0.7525 was obtained from the correlation analysis, showing that the global NAO index and rainfall variability deviate in the opposite direction. Coefficient of multiple determinations (CMD) subsequently showed value of 0.031%, being the variation in rainfall as influenced by the global teleconnectivity, and this means that the NAO index has zero or no influence on rainfall variability in Southeast region of Nigeria.