Variability of daily precipitation over Nigeria

Abstract

This study identified coherent daily precipitation regions in Nigeria by analyzing the spatial and temporal homogeneity of daily precipitation; investigating the dependence of wet day amount (WDAMT) and percentage of wet day (PWD) on latitude, longitude, elevation and distance from the ocean and finally regionalizing the daily precipitation stations. Non-parametric spatial homogeneity test was carried out on daily precipitation over 23 stations in Nigeria between 1992 and 2000 while the temporal analysis was done from 1971 to 2000. Regression analysis was used to determine the dependence of WDAMT and PWD on latitude, longitude, elevation and distance from the ocean. Principal component and cluster analyses were conducted to regionalize the precipitation stations. Seven homogeneous groups of stations were identified. Elevation explains 19.9 and 4.8 % of the variance in WDAMT and PWD, respectively, while latitude explains 76.2 % of variance in PWD. Eight principal components that explain 63.1 % of the variance in the daily precipitation data were retained for cluster analysis. Precipitation in the six daily precipitation regions that emerged from the cluster analysis is influenced by the Inter-tropical Convergence Zone, latitude, distance from ocean and southwesterlies while the northern region alone is influenced by the African Easterly Wave. In addition, precipitation in all the regions is influenced by topography. Low to medium spatial coherence exists in the precipitation regions. The spatial variations of PWD and WDAMT have implications for agricultural productivity and water resources in different parts of the country.