Interconnection of Climate Parameters and Reference Evapotranspiration over Nigeria

This study investigated temporal variations in reference evapotranspiration (ETo) and its interconnection with climate parameters across four climatic regions in Nigeria over a 42-year period (1979-2021). The ETo datasets were collected from the Archive of ECMWF-ERA-5 at a resolution of 0.25° by 0.25° grid system over Nigeria. The interconnection analyses between ETo and climate parameters (air temperature, relative humidity, wind speed and net radiation) were conducted using the cross-correlation test, Mann-Kendall tests, and four homogeneity tests at a 5% significance level. The results demonstrated strong correlations between ETo and relative humidity (RH) in the Sahel, Guinea Savannah, and Coastal regions, with R2 values of 0.7343, 0.8418, and 0.7662, respectively. Trend analysis using the Mann-Kendall test indicated significant increasing trends in ETo for the Sahel, Guinea Savannah, and Rainforest regions, while the Coastal region exhibited a significant decreasing trend. Change point analyses using the four homogeneity tests revealed that ETo experienced significant changes primarily in 1999 in the Sahel and Guinea Savannah regions, 1996 in the Rainforest region, and 2006 in the Coastal region. In conclusion, relative humidity emerged as the most sensitive parameter to ETo, with immediate response time lags observed in the Sahel and Guinea Savannah regions, and a one-month response time lag in the Rainforest and Coastal regions of Nigeria.