FLUCTUATIONS IN THE ONSET, TERMINATION AND LENGTH OF THE GROWING-SEASON IN NORTHERN NIGERIA

A simple water balance method is used to compute the dates of the onse t and termination and length of the growing season from long-term rain fall series in northern Nigeria. For most of the stations, the time se ries of onset and termination dates and growing season length are homo geneous and random, and can be taken as normally distributed. There is a progressive decrease in the length of the growing season from a mea n of about 200 days in the south to less than 155 days in the extreme northern part. While there is no statistically significant trend in th e onset dates, there is some evidence for statistically significant de creasing trend in the termination dates and the length of the growing season over the region. The results indicate that recent trends in the length of the growing season are more sensitive to large interannual fluctuations in the start of the rains than to variations in the cessa tion dates.