TEMPORAL TREND IN DAILY RAINFALL INTENSITY IN A CHANGING CLIMATE IN THE MIDDLE BELT REGION OF NIGERIA

Abstract

The study analyzed the temporal variability of daily rainfall intensity of selected stations in the
Middle Belt region (MBR) of Nigeria for 46-year period (1961-2006). Daily rainfall (≥0.3mm)
data were collected from eight weather stations in the study area. Daily rainfall intensity
categories were classified into six categories using percentiles (P) namely; extremely light (≤
P10), light (P11 - P20 ), moderately light (P21 – P50), moderately heavy (P51 – P80), heavy
(P81 – P90) and extremely heavy (> P90). To compute the percentile threshold values of the six
daily rainfall intensity categories, the population of rain days was first extracted then ranked. The
threshold values of the percentiles were extracted for each of the eight stations and the annual
number of daily rainfall for each station were then determined. Trend in the series of the six daily
rainfall intensity classes is analyzed using Mann Kendall’s test statistics (τ) and the values
obtained are plotted to show the temporal variability in the region. The result shows a general
increasing trend towards the light and extremely light intensity categories, though the rate of
increase varies across stations and with time ranges. Light rains are increasing in the Jos plateau
whereas the number of heavy events are on the decline. There is a peculiar situation in Makurdi
where both extremely light and extremely heavy intensity conditions are observed to be
increasing. ...