Eighty-year variability in rainfall in northern Nigeria and its effect on aquifer recharge

摘要

The northern part of Nigeria above latitude 11° falls in the Sudan Savanna and Sahel zones, with some 30 million people, mostly farmers growing rain fed millet sorghum, and grass for ruminant animals. The agrarian and semi-nomadic communities source domestic water from seasonal brooks, rivers and hand dug wells. The study seeks to understand the relationship between rainfall quantity and groundwater recharge, and therefore is able to predict quantity of water obtainable in these cisterns. Annual rainfall data collected from weather stations, as reported in various secondary sources for the four principal towns in the region: Sokoto, Kano, Katsina and Maiduguri for a period of 80 years (1920-2000), were analysed in comparison with rate of changing water levels in the hand dug wells in Mulgwe in the Chad basin. In all the stations, rainfall gently oscillated around the mean during the period 1920 and 1960 after which it started to dramatically decrease. Thus, average rainfall in Maiduguri during the periods 1920-1960, and 1965-2000 were 832.4 and 554.0 mm, respectively. Water level measurements in Mulgwe hand dug wells in the Chad basin between 1964 and 1973 show that water level reduced by as much as 735 cm within the 10-year period. Regression analysis between annual rainfall and yearly water level decline in the well shows r = 0.634, thus revealing a close association between these factors. There is therefore a need to mitigate climate change by reducing the prevalent deforestation and the continuous gas flaring in Nigeria.