Agroclimatic Zonning of Nigeria Based on Rainfall Characteristics and Index of Drought Proneness

Abstract

Nigeria, a country in sub-Saharan West Africa that depends largely on rainfall distribution for its agricultural practices has been categorised into three major climatic zones based on its rainfall characteristics and drought-proneness analysis. The data used comprises of daily rainfall of thirty years (1983 to 2012) for the thirty-eight climatic stations spread over the country. Rainfall characteristics such as onset dates, cessation dates, length of rainy season and rainfall amount within the seasons for thirty years were extracted over each of these stations for the analysis. Rainfall distribution during the rainy season was also investigated by using two-state Markov chain analysis of order one and two.

The result is useful in making some pre-sowing decisions such as site selection for a particular crop and specie selection for a particular zone. The first zone has earliest rainfall onset dates, latest cessation dates and hence, having longest length of rainy season in the country. It also has the highest (lowest) Markovian probability of a wet (dry) week after a previously wet week and hence least prone to drought occurrence. Therefore, this zone is tagged “rain-forest” (Guinea). Followed closely is the zone II which is the “Savannah” and lies on the north of the zone I. On the northern part of zone II is the zone III with the shortest length of rainy season termed “Sahel”. Despite the fact that Sahel zone has the latest onset, earliest cessation and hence shortest length of rainy season, it is most prone to drought occurrence, while Savana has moderate values between those of zones I and III.

Keywords: Rainfall onset, rainfall cessation, length of rainy season, drought-proneness, zones.