Comparison and modification of equations for calculating evapotranspiration (ET) with data from Gansu Province, Northwest China

Abstract

A total of 11 empirical evapotranspiration equations were developed by Hargreaves (1975), Hargreaves (1985), Makkink, Turc, Priestley-Taylor, Jensen-Haise, Doorenbos and Pruitt, Abtew, McGuinness and Bordne, Rohwer and Blaney-Criddle. These were compared with pan evaporation data measured at 10 stations in Gansu Province, northwest China. The comparison was first made using the default values in each of the 11 equations, and then redone using calibrated coefficient values. The calibration was made for all 11 equations using the climatic index P a /P g . The results show that using default coefficient values resulted in large errors for all equations. The largest error was found in the comparison results of the Turc, and McGuinness and Bordne equations. The Turc and Jensen-Haise equations should be used to estimate the daily evapotranspiration (ET) under the conditions of T mean > 0 and T mean > À38C, respectively, when applied to northwest China. Based on the comparison results of before and after recalibration, the Doorenbos and Pruitt method is more suitable to the arid, semiarid and wet regions in northwest China. The accuracy of the results for determining monthly ET greatly improved when calibrated coefficient values were introduced to the 11 equations, except for McGuinness and Bordne, Abtew, and Blaney-Criddle, which need to be recalibrated using two parameters. Thus, it can be concluded that calibration can be used to modify evapotranspiration equations with multi-station data to improve the accuracy of evapotranspiration estimates in northwest China. Copyright # 2009 John Wiley & Sons, Ltd. la province de Gansu, Chine du Nord-Ouest. La comparaison a été effectuée en utilisant les valeurs par défaut dans chacune des 11 équations, et ensuite refaite avec des valeurs de coefficient calibrées. L'étalonnage a été fait pour les 11 équations à l'aide des indices climatiques Pa/Pg. Les résultats montrent que l'utilisation des valeurs par défaut des coefficients a donné lieu à de grosses erreurs pour toutes les équations. La plus grosse erreur a été trouvée avec les équations de Turc, McGuinness et Bordne. Les équations de Turc et de Jensen-Haise doivent être utilisées pour estimer l'évapotranspiration (ET) quotidienne dans les conditions de T moyenne > 0 and T motenne > À38C respectivement, lorsqu'elles sont appliquées à la Chine du Nord-Ouest. Sur la base de la comparaison des résultats avant et après réétalonnage, la méthode de Doorenbos et Pruitt est plus appropriée pour les zones arides, semi-arides et humides dans les régions du Nord-Ouest de la Chine. La précision des résultats pour déterminer ET mensuelle est grandement améliorée lorsque les valeurs calibrées des coefficients ont été introduites pour les 11 équations, à l'exception de McGuinness et Bordne, Abtew, et Blaney-Criddle, qui doivent être étalonnées en utilisant deux paramètres. Ainsi, il apparaît que l'étalonnage peut être utilisé pour modifier les équations de l'évapotranspiration avec de données multi-station afin d'améliorer la préci...

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