Rainfall is the most important climatic factor for most living organisms in the tropics, including Nigeria. The amount and distribution of annual rainfall directly determine the type of vegetation zones (e.g., rainforest in the south, savanna in the north). The type of plants present, in turn, determines the types of animals and microorganisms that can survive in that region, thus affecting the entire community of organisms.

Although, temperature and humidity are important, rainfall is the primary determinant of the major biomes and the overall distribution of life in Nigeria.