Trends in Aridity of the Arid and Semi-Arid Regions of Northern Nigeria

Aridity index (AI) is a numerical indicator of the degree of dryness of the climate at a given location. These indicators serve to identify and delimit regions that suffer from a deficit of available water, a condition that can severely affect the effective use of agricultural land and water resources development. The focus of this paper is to determine the trend and map out the aridity of the drought prone areas of northern Nigeria. Three decade’s (1981–2010) annual rainfall and, minimum and maximum temperature records for 11 synoptic meteorological stations were collected from NIMET Office, Lagos and used. De Martonne’s aridity index formula was applied to the data and aridity indices were derived for the region. The derived aridity indices were subjected to time series analysis and classification of the region into aridity zones was carried out based on the derived aridity indices from which an aridity map of the region was produced. Results of the time series analysis show that only Kaduna indicated a decreasing aridity while the other stations exhibit a significantly positive tendency towards increasing dryness. The region is classified into four aridity zones based on the aridity indices as: slightly humid zone (Kaduna and Zaria areas), moderately arid areas (Yelwa, Gusau, Kano and Bauchi), semi arid regions (Sokoto, Potiskum, Maiduguri) and the arid zone (areas around Nguru, Hadejia and Kano). It is concluded that the drought prone areas of northern Nigeria are witnessing increasing aridity which accounts for the shrinking of most dams and other surface reservouirs in the region. This has necessitated accessing of underground water from even the third aquifer at some locations. It is recommended therefore, that the dredging of all the existing dams in northern Nigeria be undertaken in order to improve the storage of more water, just as proper water policy for its sustainable use be formulated by Nigeria. Keywords: aquifer, aridity, drought, dryness, Indices, time series