Effect of Climatic Variability on Drought Occurrence Probability over Nigeria

Drought is grouped into meteorological, hydrological and agricultural classes. These classifications are done according to a number of criteria involving several variables, used either alone or in combination: rainfall, temperature, humidity, and evaporation from free water, transpiration from plants, soil moisture, wind, river and stream flow, and plant condition. The study extracted meteorological data including near surface temperature, relative humidity and precipitation averaged for the month of July covering a period of 1975 – 2014 grouped into 2 regimes of 20 years each. The data were analyzed using drought empirical models suitable for deducing meteorological, agricultural and hydrological drought phenomena with a view to deduce drought probability trend across Nigeria. Highly significant increase in atmospheric dryness was observed at Sokoto, Katsina, Maiduguri, Kaduna and Yola. Slight increase was observed at Kano, Abuja, Makurdi, Lagos, Osogbo, Benin, Enugu, Port Harcourt and Calabar. A slight decrease in atmospheric dryness was observed in one station only – Jos from all the stations under consideration. All stations across Nigeria had a significant increase in dryness ratio for monitoring agricultural drought. Stations in the southern part of Nigeria had no significant change in drought occurrence probability except at Osogbo where a slight increase in drought occurrence probability was observed. Generally, the results offered a significant insight into occurrence probability of drought over Nigeria by comparing trends in two regimes of 20 years, respectively. A shift from wet to dry climatic in features was observed across Nigeria confirming gradual occurrence of drought in the past 20 years over Nigeria.