Evaluation of nine reference evapotranspiration models in Traghen region, Southwest of Libya

Abstract

This research was carried out to evaluate nine reference evapotranspiration, and find out an alternative models to the standard FAO Penman-Monteith model in Traghen region southwest of Libya. The models applied were standard FAO Penman-Monteith, FAO Radiation, FAO Blaney-Criddle, Hargreaves-Samani, Priestley-Taylor, Makkink, Turc, Thornthwaite, Kharrufa and McCloud.  The models were compared with the FAO Penman-Monteith model using root mean square error (RMSE) , mean bias error (MBE), Pearson type goodness of fit index (R2), refined index of agreement (dr), modeling efficiency (Ef) and t-test.  Results showed that FAO Radiation and FAO Blaney-Criddle models overestimated ETo by values ranged from 0.64% to 16.06%.  However, Kharrufa and McCloud models overestimated ETo in some months and underestimated ETo in some other months.  Whereas, the other models underestimated ETo by values ranged from -86.69 % to -6.02%.  The FAO radiation model gave the highest dr (0.892) and Ef (0.951) values, and the lowest RMSE (0.534 mm/day), indicating that this model was the best alternative to the FAO Penman-Monteith model in the study region, followed by FAO Blaney-Criddle model with dr value of 0.851, Ef value of 0.878, and RMSE value of 0.845 mm/day.  In addition, FAO radiation model showed the second best R2 and MBE values at 0.993 and 0.473, respectively  Also, FAO Blaney-Criddle model showed the third best R2 value at 0.989.  Therefore, FAO radiation model is ranked the first and FAO Blaney-Criddle model is ranked the second.  According to the statistical measures stated above, Turc model ranked the third, Kharrufa model ranked forth.  Models of Hargreaves-Samani, Makkink, Priestley-Taylor, McCloud and Thornthwaite ranked fifth, sixth, seventh, eighth and ninth, respectively.  T-test analysis at 5% level of significance indicated that there is a significant difference between the FAO Penman-Monteith model and all models except Kharrufa and McCloud models.