Changes in rainfall characteristics in northern Nigeria

This study examines recent changes in several rainfall characteristics in northern Nigeria. The records at 25 locations were analyzed for the occurrence of abrupt changes and trends using the Pettitt and the Mann-Kendall tests. Variables analyzed included annual total rainfall and number of rain days, the dates of onset, termination and duration of the rainy season as well as monthly rainfall, monthly number of rain days and various categories of rainfall above certain intensities. An abrupt change occurred in the time series of annual rainfall, number of rain days and affected areas north of latitude 11° N. However, the sub-periods prior to and after the change points may be considered to be homogenous. The series of variables related to the duration of the rainy season exhibit no significant trends or jumps. It is concluded that recent changes in rainfall over the Sahel were driven by a reduction in the frequency of rain days of high rainfall intensities during the months of August and September. The fact that the high intensity rainfall does not contribute significantly to crop growth may explain the continuation of agricultural activities in the Sahel despite massive reductions in annual rainfall. © 1998 Royal Meteorological Society