Evaluating the best evaporation estimate model for free water surface evaporation in hyper-arid regions: a case study in the Ejina basin, northwest China

Abstract

Free water surface evaporation is an important process in the hydrologic and energy cycle. Accurate calculation of free water evaporation helps in evaluating the reliability of data on the distribution and quantity of water resources. However, the applicability of evaporation models to the calculation of free water surface evaporation in hyper-arid regions is still uncertain. Moreover, the accuracy of previously used evaporation models should be evaluated for hyper-arid regions. In this study, the Ejina basin in the hyper-arid region of northwest China was selected to address this issue. Measured meteorological data (1993–2008) were used to calculate free water surface evaporation using the Dalton model, Penman formula, and energy balance equations. Results from two different Dalton models were higher and lower than the results from E601 pan evaporation, respectively. Results from the Penman formula were lower than results from E601 pan, whereas results from the energy balance equations are higher than the results from E601 pan. The results indicate that previous evaporation models are not suited for calculating free water surface evaporation in hyper-arid regions if not modified. Using meteorological data and radiation data (1993–2000), the Dalton model, energy balance equations, and Penman formula were modified to calculate free water surface evaporation for 2001–2008. The average annual evaporation from the three modified models was slightly lower than the evaporation from E601 pan during 2001–2008. However, the errors in the values were only 11–14 mm, which were much lower than in previous models. The modified Dalton model and Penman formula yielded a higher accuracy of the calculation, whereas the modified energy balance equations had the lowest accuracy.