Diurnal solar energy and temperature changes over Nigeria using satellite data

Abstract

This study investigated the diurnal variability of global horizontal irradiance (GHI) and surface temperature across Nigeria’s major climatic zones. Daily all-sky surface shortwave downward irradiance and 2-m air temperature data spanning 2001–2023 were obtained from the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2). The daily datasets were aggregated into monthly means and analyzed across four climatological seasons. Daily variability was quantified using standard deviation, while long-term trends were assessed using simple linear regression, with statistical significance evaluated at p < 0.05. The relationship between GHI and surface temperature was examined using Pearson’s correlation coefficient. Results show that daily GHI variability was highest in the southern tropical monsoon and tropical rainforest zones, whereas daily temperature variability was greatest in the northern warm desert and warm semi-arid regions. Monthly analysis revealed that GHI peaked in April over northern zones but reached maximum values in February across other regions. Surface temperature was highest between March and May, but lowest in August for the tropical monsoon, tropical rainforest, and Mediterranean climates; January for the warm semi-arid and warm desert climates; and December for the tropical savanna climate. Correlation analysis indicated very weak to moderate relationships between GHI and surface temperature. Regression results revealed a very weak to weak positive relationship, with significant differences across all locations examined ($p < 0.0001$). Long-term trends showed a slight increase in GHI across all climatic zones, while surface temperature increased marginally in most regions except the northern warm semi-arid and warm desert zones.