LINEARIZATION OF EVAPOTRANSPIRATION RATE IN NIGERIA USING AGRO-CLIMATIC DATA FOR COMPARING REFERENCE EVAPOTRANSPIRATION MODELS

Abstract

The study presents Linearization of Evapotranspiration Rate in Nigeria using Agro-Climatic Data for Comparing 
Reference Evapotranspiration Models in order to prevent over or under irrigation by farmers, which could have a 
detrimental impact on crop yields. Agro-climatic data from 2013 to 2024 were gathered and examined for this study. 
Minimum and maximum temperatures (oC), relative humidity (%), wind speed (km/day), sunlight (hr/day), and 
radiation (MJ/m2/day) were the data collected. Using the mean monthly agro-climatic data for the six chosen agro
climatic weather stations in Nigeria [North-East (Yola), North-West (Sokoto), North-Central (Lokoja), South-East 
(Enugu), South-West (Lagos), and South-South (Port-Harcourt)], and FAO Penman-Monteith model was utilized as 
a universal standard model to calculate the mean monthly reference evapotranspiration (ETo). The mean monthly 
reference evapotranspiration (ETo) was calculated using five different evapotranspiration models (Priestley-Taylor 
model, Thornth-Waite model, Hargreaves model, ASCE-Penman Monteith model, and Blaney-Criddle model). The 
results were then compared with the standard FAO Penman-Monteith model. The FAO Penman-Monteith model's 
estimates and the reference ETo estimates from the five models were compared using statistical regressions. According 
to the findings, the six agro-climatic weather stations' mean monthly average ETo estimates from the FAO Penman
Monteith model, Priestley-Taylor model, Thornth-Waite model, Hargreaves model, ASCE-Penman Monteith model, 
and Blaney-Criddle model were, respectively, 6.48, 7.66, 14.14, 11.16, 5.57, and 3.70 mm/day. The ASCE-Penman 
Monteith model, which has a strong correlation with the FAO Penman-Monteith model, was the strongest predictor; 
the Priestley-Taylor model was the second-best. The Blaney-Criddle model significantly overestimated the FAO 
Penman-Monteith model, whilst the Thornth-Waite and Hargreaves models yielded underestimated ET values. The 
models exhibit significant diversity and the relationship between them is location-dependent. The ASCE-Penman 
Monteith model and Priestley-Taylor model can be used in the absence of FAO 56 Penman-Monteith model. Both 
Blaney-Criddle model, Thornth-Waite and Hargreaves model are not suitable for use for regional water resource 
planning and accurate agricultural water management.