|Gao, Fei - Beijing Normal University|
|Ouyang, Ying - Forest Service (FS)|
|Wang, Huixiang - Beijing Normal University|
|Fisher, Daniel - Ken|
Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2017
Publication Date: 6/5/2017
Citation: Gao, F., Feng, G.G., Ouyang, Y., Wang, H., Fisher, D.K., Adeli, A., Jenkins, J.N. 2017. Evaluation of reference crop evapotranspiration methods in arid, semi-arid and humid regions. Journal of the American Water Resources Association. doi:10.1111/1752-1688.12530.
Interpretive Summary: In order to select simpler ETo calculation methods for different climatic regions, the FAO-56 Penman-Monteith and six alternative ETo methods were compared based on monthly averages of daily ETo, total annual ETo, and daily ETo in Aksu (arid region), Tongchuan (semi-arid region), and Starkville (humid region). The Prs-Tylr and 1985 Har methods can be used as substitutional method to FAO-56 method for calculating monthly averages of daily ETo, total annual ETo, and daily ETo in both arid and semi-arid regions, while in the humid region, the 1957 Makk can be used. The results suggest that different climates need different methods to calculate ETo, and that these simple alternative methods can be used when the full weather data sets required by the FAO-56 Penman-Monteith method are not available. Results also show that caution should be used when applying these methods in a specific site since the performance of the same simple method may differ greatly. It is necessary to check the performance of the simpler methods which were tested somewhere else by making comparison with FAO-56 method even if the climate of a selected area is similar to that tested in previous studies.
Technical Abstract: It is necessary to find a simpler method in different climatic regions to calculate reference crop evapotranspiration (ETo) since the application of the FAO-56 Penman-Monteith method is often restricted due to unavailability of a full weather data set. Seven ETo methods, the de facto standard FAO-56 Penman-Monteith, and six alternative methods, the FAO-24 Radiation, FAO-24 Blaney Criddle, 1985 Hargreaves, Priestley-Taylor, 1957 Makkink, and 1961 Turc, were applied to calculate monthly averages of daily ETo, total annual ETo, and daily ETo at Aksu, China, in an arid region, Tongchuan, China, in a semi-arid region, and Starkville, Mississippi, USA, in a humid region. Comparisons were made between the FAO-56 method and the six simple alternative methods using the index of agreement D, modeling efficiency EF, and root mean square error RMSE. For the monthly averages of daily ETo, the values of D, EF, and RMSE ranged from 0.88 to 0.98, 0.87 to 0.98, and 0.28 to 0.89 mm d-1, respectively, in the arid region; from 0.92 to 0.98, 0.85 to 0.97, and 0.23 to 0.55 mm d-1, respectively, in the semi-arid region; and from 0.82 to 0.95, 0.55 to 0.91, and 0.43 to 1.00 mm d-1, respectively, in the humid region. For the total annual ETo, the values of D, EF, and RMSE ranged from 0.32 to 0.84, -8.38 to 0.65, and 38.12 to 197.42 mm yr-1, respectively, in the arid region; from 0.40 to 0.91, -7.99 to 0.82, and 24.80 to 172.98 mm yr-1, respectively, in the semi-arid region; and from 0.21 to 0.75, -43.08 to 0.22, and 47.34 to 234.08 mm yr-1, respectively, in the humid region. For the daily ETo, the values of D, EF, and RMSE ranged from 0.86 to 0.97, 0.74 to 0.96, and 0.41 to 1.00 mm d-1, respectively, in the arid region; from 0.89 to 0.97, 0.81 to 0.97, and 0.30 to 0.71 mm d-1, respectively, in the semi-arid region; and from 0.58 to 0.86, 0.57 to 0.91, and 0.49 to 1.06 mm d-1, respectively, in the humid region. The Priestly-Taylor and 1985 Hargreaves methods worked best in the arid and semi-arid region, while the 1957 Makkink worked best in the humid region. It is necessary to check the performance of the simpler methods even if the climate of a selected area is similar to that tested in previous studies.