Abstract
Potential evapotranspiration (PET) is crucial for water resources assessment. In this regard, the FAO (Food and Agriculture Organization)–Penman–Monteith method (PM) is commonly recognized as a standard method for PET estimation. However, due to requirement of detailed meteorological data, the application of PM is often constrained in many regions. Under such circumstances, an alternative method with similar efficiency to that of PM needs to be identified. In this study, three radiation-based methods, Makkink (Mak), Abtew (Abt), and Priestley–Taylor (PT), and five temperature-based methods, Hargreaves–Samani (HS), Thornthwaite (Tho), Hamon (Ham), Linacre (Lin), and Blaney–Criddle (BC), were compared with PM at yearly and seasonal scale, using long-term (50 years) data from 90 meteorology stations in southwest China. Indicators, viz. (videlicet) Nash–Sutcliffe efficiency (NSE), relative error (Re), normalized root mean squared error (NRMSE), and coefficient of determination (R2) were used to evaluate the performance of PET estimations by the above-mentioned eight methods. The results showed that the performance of the methods in PET estimation varied among regions; HS, PT, and Abt overestimated PET, while others underestimated. In Sichuan basin, Mak, Abt and HS yielded similar estimations to that of PM, while, in Yun-Gui plateau, Abt, Mak, HS, and PT showed better performances. Mak performed the best in the east Tibetan Plateau at yearly and seasonal scale, while HS showed a good performance in summer and autumn. In the arid river valley, HS, Mak, and Abt performed better than the others. On the other hand, Tho, Ham, Lin, and BC could not be used to estimate PET in some regions. In general, radiation-based methods for PET estimation performed better than temperature-based methods among the selected methods in the study area. Among the radiation-based methods, Mak performed the best, while HS showed the best performance among the temperature-based methods.
Highlights
Evapotranspiration (ET) plays an important role in maintaining water balance of terrestrial ecosystem
Potential evapotranspiration (PET) Estimated by Food and Agriculture Organization (FAO)–Penman–Monteith method (PM) Method in the Four Sub-Regions
Sichuan basin showed the minimum values at all time except summer, whereas the eastern margin of the Tibetan
Summary
Evapotranspiration (ET) plays an important role in maintaining water balance of terrestrial ecosystem. Accurate assessment of evapotranspiration is essential for efficient irrigation management, water resources management, crop production, environmental assessment, ecosystem modelers and solar energy system [1,2,3,4]. Water 2017, 9, 734 the actual evapotranspiration, which was otherwise difficult to estimate by lysimeter measurement and water balance approach under field conditions [5,6]. PET is useful to measure the atmospheric water demand of the region and could be used for various applications including irrigation scheduling, drought monitoring, and understanding climate change impacts. Recently PET or reference ET has been widely used in the computation of actual ET using different remote sensing based models [7,8,9]. As an input in different ET model, PET could be used in monitoring actual ET of a region. PET is considered the same as reference crop evapotranspiration ET, which is defined by Allen et al [10] as a hypothetical evapotranspiration in regard to an assumed crop height of 0.12 m, a fixed surface resistance of 70 s/m, an albedo of 0.23, and the reference surface closely resembling an extensive surface of green grass of uniform height, actively growing, well-watered, and completely shading the ground
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