Spatio-temporal variations in thunderstorm rainfall over Nigeria

Thunderstorm rainfall is a major form of convective rainfall over Nigeria. Its contribution to total wet season rainfall increases from about 18% in the south to 36% in the north. The importance of thunderstorms lies in the fact that they contribute significantly to flooding episodes and soil erosion processes due to their high intensity and torrential characteristics. This paper examines the spatial and temporal variations in thunderstorm rainfall over Nigeria using daily rainfall data and associated weather information over a 30 year period (1960-1989) for 19 synoptic stations. Results show that the dry season distribution pattern of rainfall due to thunderstorms shows a general decrease from south to north similar to the total rainfall distribution pattern in the country. At the peak of the wet season (July-September) thunderstorm rainfall increases northwards up to around latitude 11 degrees N when it begins to decrease. The effect of orography in enhancing thunderstorm rainfall across the country is also shown. Elementary linkage analysis was used to group the 19 synoptic stations into thunderstorm rainfall regions. Six regions were identified which showed internal coherence in terms of temporal fluctuations of thunderstorm rainfall. (C) 1998 Royal Meteorological Society.