Intercomparison of Model-Estimated Potential Evapotranspiration on the Tibetan Plateau during 1981–2010

Abstract

AbstractPotential evapotranspiration (PET), the maximum evapotranspiration rate under unlimited water supply, reflects the capacity for transpiration flow and plant primary production. Numerous models have been developed to quantify PET, but there are still large uncertainties in PET estimations. In this study, the authors conducted spatially explicit estimations of daily PET from 1981 to 2010 for eight different land-cover types on the Tibetan Plateau by applying three types of PET models including a combination model (Penman?Monteith), a radiation-based model (Priestley?Taylor), and a temperature-based model (Thornthwaite). This study found that the PET estimated by Thornthwaite model (PETT) was lower than those estimated by Priestley?Taylor (PETPT) and Penman?Monteith models (PETPM). Penman?Monteith model gave the highest estimates of PET on annual and daily scales. The mean annual PET for the whole plateau estimated by these three models varied from 675.1 to 700.5 mm yr?1, and daily PET varied from 1.33 to 1.92 mm day?1. The spatial pattern of PETT did not agree with the PETPT and PETPM, while the latter two agreed well with each other. Because of different model structures and dominant meteorological drivers, the interannual variability of PET varied significantly among the models. PETPT and PETPM showed a transition around 1993 since the dominant meteorological drivers were different before and after 1993. These disagreements among different models suggested that PET models with different algorithms should be used with caution. This study provided a validation to assist those undertaking PET estimations on the Tibetan Plateau.