Characterizing Dry and Wet Spell in a Changing Climate in the Middle Belt Region of Nigeria

The spatial variation and trend in the observed frequencies, and weekly probabilities of dry and wet Spell were analysed from 1981 – 2010 in the Middle Belt region (MBR) of Nigeria. Daily rainfall (mm) data were obtained from eight synoptic weather stations spread across the region. Dry spell was classified into four categories of 2-4 days, 5-7 days, 8-10 days and greater than 11 days duration and wet spell was classified into two categories of 2-4 days and greater than 5 days duration. Coefficient of variation (CV), correlation and Markov Chain probability model were used to analyse the spatial variation, trend and the probabilities of occurrences of dry and wet weeks. The spatial CV range increases from 12.8% (2-4 days) to 110.1% (>11 days) for dry spell and 16.7% (2-4 days) and 192.5% (>5 days) for wet spell. There is a generally decreasing and increasing trend in the frequencies of dry and wet spell in the MBR. The mean regional onset and cessation of the rainy season is 15^th week (9^th – 15^th April) and 42^nd week (15^th – 21^st October). The probability of occurrences of initial and conditional probability is more than 50% from the 22^nd week at 8.4mm per week threshold. The study concludes that land preparation for planting should commence from 20^th to 22^nd week, and Irrigation farming should start after the 42^nd week in the MBR.