Modification of blaney-morin-nigeria evapotranspiration model for Asaba and Uyo, South-south Nigeria

Abstract

The study was designed to re-examine and modify the Blaney-Morin-Nigeria (BMN) evapotranspiration (ET) model which was developed for Asaba and Uyo in South-south of Nigeria. This was achieved using a non-linear iterative technique based on Levenberg-Marquardt algorithm, making use of climatic variables. The newly developed model constants were H = 288.0, m = 0.96; H = 285.8, m = 0.91 and H = 287.0, m = 1.00 for South-south Nigeria, Asaba and Uyo respectively compared to the H = 520.0, m = 1.31 for the original BMN ET model. Data were analysed using different statistical models. The three newly developed BMN models when compared with FAO-56 PM model which was used as standard gave a more satisfactory RET estimates than the original BMN ET model when compared with FAO-56 PM model. In Asaba, result showed that the original BMN, the BMN for Asaba and the BMN for south-south underestimated FAO-56 PM RET by 9.87%, 2.70% and 7.14% respectively, while in Uyo, the original BMN model and South-south model overestimated FAO-56 PM RET by 4.19% and 3.99% respectively, whereas that for Asaba underestimated by 1.83%.  The comparative analysis using statistical indices showed that the new BMN models gave a better prediction of RET than the original BMN model. The location specific models for Asaba and Uyo predicted RET best among the evapotranspiration models followed by the South-south model and the original BMN model gave the worst prediction.