## 4 Discussion  
This study used PML-V2 ET and its component products generated at 500 m and 8-day resolution. The validation result showed that it had good performance in modeling ET compared with MOD16 ET (R\({}^{2}\) = 0.86) in TGRA. However, the accuracy of the MOD16 ET product also needs to be evaluated as it underestimated the ET for semiarid area [49] and overestimated for forested areas [50; 51]. Moreover, the FAO-56 Penman-Monteith model used in MOD16 was limited due to the lack of required weather data in many regions [52], and the heterogeneity of land use [53], uncertainty in measuring soil water status [54], and complex dynamic changes in vegetation [36] also affecting the evaluation of ET, which were ignored in ET models. Moreover, due to the absence of the lysimeters, isotopes, and sap flux in TGRA, the ET components were not verified in this study. Therefore, the sites that measured ET and its components in TGRA are likely to be built and a more accurate validation method is needed to carry out future research. The average annual ET in TGRA was 585.12 mm, which was higher than the average ET of 406 mm across China [55], and much higher than the ET in arid and semiarid regions in western China, such as the Loess Plateau [56] and Tibetan Plateau [6], while it was much lower than ET in humid regions in eastern China [55]. Ec accounted for 56.06% of ET and it was the most important ET component in TGRA. The contribution of Ec to ET was reasonable compared with the results of 0.20-0.65 for global terrestrial ecosystems [57], 0.52-0.59 for Chinese terrestrial ecosystem [19], while it was much lower than that for the Yangtze River Basin, where the Ec accounted for 65% of ET [58], and was higher than that for the Yellow River Basin, where the proportion of Ec to ET was 48% [59]. Es accounted for 29.64% of ET in TGRA, which was lower than 0.55 across China [60], and much lower than the proportion for the Tibetan Plateau [6] and the Yellow River Basin [59] in semiarid regions in western China, while the proportion was slightly higher than that globally [13]. Ei accounted for the lowest proportion of ET in TGRA (14.3%), which was higher than 9.98% on a global scale [13]. Due to the difference in climatic features, hydrological regimes, vegetation, and soil coupled with the methodology and data, the proportion of ET components varied from region-to-region [18; 19]. Generally, Ec accounted for the major part of ET globally and in most regions [13; 18], especially in vegetated systems with low precipitation, Ec was the most important part among the three components [18]. While for areas in deserts and the Plateau with low vegetation coverage, yet high precipitation and temperature, Es was the predominate part [6; 13]. Ei depended on the precipitation and canopy status. Compared to Ec and Es, it accounted for a little proportion of ET, while it was an indispensable component of surface water balance, particularly for the vegetated areas with higher vegetation coverage and leaf area index [22]. The mean annual ET did not show a significant change in TGRA from 2000 to 2020; this was consistent with the results from previous studies for TGRA [33; 36; 37]. For instance, [PERSON] et al. [36] found that the annual ET displayed an insignificant increasing trend from 1993 to 2013. [PERSON] et al. [33] reported an insignificant increasing trend of ET during 2000-2015. [PERSON] et al. [37] investigated the variation of ET using MOD16 from 2003 to 2016, and the results showed no obvious change trend. The dominant climate factors affecting the changes in ET, Ec, and Es were Ta and VPD. The result was consistent with that of [PERSON] et al. [61], who investigated the global ET from 2003 to 2019 and found that land temperature was the main driver of the ET trend. Increases in VPD and temperature combined with the decrease in relative humidity [62] increased the atmospheric demand for evapotranspiration [63]. Since the construction of TGP, the land use/land cover changed significantly in TGRA [30].