ASSESSMENT OF SIX EVAPOTRANSPIRATION MODELS FOR UMUAHIA LOCAL GOVERNMENT AREA, ABIA STATE

Penman-Monteith (PM), Priestly Taylor (PT), Blaney-Morin Nigeria (BMN), Jensen-Haise (JH), Hargreaves-Samani (HS) and Thornthwaite (TH) models were used to estimate Reference Evapotranspiration (RET) for Umuahia, in South-Eastern Nigeria from 1997to 2017. The Penman-Monteithmodel was chosen as a standard for evaluating the other five empirical models. Good correlation was found between the RET values, estimated by each of the five radiation and temperature based models and the Penman-Monteith model, although there were some discrepancies. The mean annual RET estimated by the Penman-Monteith model as the standard tool for Umuahia was found to be 1041.0mm. While the mean annual RET estimated by other five models were found to be 579.3mm, 1487.7mm, 513.7mm, 1543.3mm and 1367.7mm, respectively. Conversely, the weather parameters influencing this station were found to be high due to the flatness of the terrain. In addition, from the statistical regression analysis, Priestly Taylor (PT) had the highest T-scores and lowest Root Mean Square Error (RMSE), in the ranking the Thornthwaite, Blaney-Morin and Hargreaves-Samani predicted best among the five models in the station. Good correlation was found by the temperature based models when evaluated RET with data for Umuahia Station. The Penman-Monteith estimates was used to develop correction factors for the three models that predicted best in the station for their potential use in the areawithout sensitive error. This was done in order to achieve accurate and reliable evapotranspiration estimate.