Hydrological Processes

Thus far, measurements and estimations of actual evapotranspiration (ET) from high-altitude grassland ecosystems in remote areas like the Qinghai-Tibetan plateau are still insufficient. To address these issues, a comparison between the results of the eddy covariance (EC) measurements and the estimates, considering the Katerji and Perrier (KP), the Todorovic (TD) and the Priestley–Taylor (PT) models, was carried out over an alpine grassland (38o03'1.7” N, 100o 27’ 26” E; 3032 m a.s.l.) during the growing seasons in 2008 and 2009. The results indicated that the KP model after a particularly simple calibration gave the most effective ET values in different time scales, the PT model slightly underestimate ET at night and the TD model significantly overestimated ET at noon. In addition, the canopy resistance calculated by the TD model was completely different from that calculated using the inverted EC-measured data and the KP model, which may be due to some unrealistic assumptions made by the TD model. The KP parameters were a = 0.17 and b = 1.50 for the alpine grassland and appeared to be interannually stable. However, the PT parameter showed some interannual variations (α = 0.83 and 0.74 for 2008 and 2009, respectively). Therefore, the KP model was preferred to estimate the actual ET at both hourly and daily time scales. The PT model, being the simplest approach and field condition dependent, was recommended when available weather data were rare. On the contrary, the TD model always overestimated the actual ET and should be avoided in case of the alpine grassland ecosystems. Copyright © 2012 John Wiley & Sons, Ltd.