Spatial Distribution of Annual Rainfall Totals Across the Six Geopolitical Zones of Nigeria

Understanding the spatial gradients of annual rainfall across Nigeria is fundamental to rational planning in agriculture, water resources management, and climate policy. This study maps and analyzes the spatial distribution of mean annual rainfall totals across Nigeria's six geopolitical zones using a 30-year climatological dataset (1991 to 2020) from 34 NiMet synoptic stations distributed across the country. Inverse Distance Weighting (IDW) and kriging interpolation techniques were applied in ArcGIS to generate continuous rainfall surface maps from point station data. The resulting maps were analyzed in conjunction with Nigeria's ecological zone boundaries to assess the degree of correspondence between rainfall gradients and vegetation zone transitions. Results confirm a pronounced north-south rainfall gradient, with mean annual totals ranging from approximately 350 millimetres in the North East to over 3,200 millimetres in parts of the South South. High spatial variability was identified within the Guinea Savanna and Derived Savanna zones, attributed to complex orographic and mesoscale convective influences. The study reveals that current NiMet station density is insufficient for reliable spatial interpolation, particularly in the North West and North East zones. Recommendations focus on strategic densification of the national observing network and adoption of satellite-merged rainfall products to supplement sparse in-situ measurements. Keywords: rainfall distribution, spatial interpolation, Nigeria, climatology, NiMet.