Rainfall Intensity and Evapotranspiration Patterns Nexus over Nigeria in Different Solar Cycles

The study employed Mass – Transfer Model (MTM) to estimate evapotranspiration (ET) from 12 selected locations spread across three climatic zones over Nigeria at intervals of 30 years (1988 and 2018) depicted by different solar cycles. Based on this finding the impacts of rainfall intensity on evapotranspiration patterns over Nigeria were investigated. Daily averaged values of wind speed at 2 m from soil, air temperature and relative humidity for 12 selected stations across Nigeria were employed for 1988 and 2018. The actual vapour pressure and saturated vapour pressure were estimated. A correlation between evapotranspiration with rainfall intensity was established to determine impacts of rainfall intensity on evapotranspiration patterns over Nigeria in solar maxima and minima scenarios. The results showed that ET was higher in 2018 than 1988 in 3 out of 4 stations in tropical monsoon; in tropical savannah and only Ibadan and Akure had a reduction in these values when 1988 was compared with 2018. Lowest values of ET was observed between August and October corresponding to the peak of rainy season. 7 stations out of 12 were influenced by solar minima phenomenon namely Port Harcourt, Owerri, Enugu, Ibadan, Minna, Borno and Gusau. The lowest values of ET were recorded at Calabar and Port Harcourt for both 1988 and 2018 while the highest values were observed at Borno for 1988 and Sokoto for 2018. Rainfall intensity had greater impacts on ET values in tropical monsoon than any other climatic zone in Nigeria.