# Evapotranspiration in Dynamic of Highland Barley Using PML ET Product in Tibet
## 3 Results and Discussion
### Seasonal Variations in ET Components  
The temporal distributions of the daily ET components are presented in Figure 3. ET components of high-hand barley showed similar seasonal variation patterns at different altitude zones; they increased progressively from the beginning of the year and reached the maximum in August, and then they declined dramatically to the end of the year, while the peak time for Ei (Figure 3e) was slightly later than that for ET (Figure 3g) and Ec (Figure 3c). The peak time for Es differed greatly across different altitude zones (Figure 3a); Es at 3700-3800 m altitude zone reached the maximum on the 161 st day in June, which was much earlier than those for other altitude zones. The maximum Es at 3900-4100 m altitude zone occurred on the 217 th day, which was consistent with ET and Ec, and the maximum Es was observed on the 185 th day in early July for other altitude zones. Figure 3: Temporal trends of Es (**a**), Es/ET (**b**), Ec (**c**), Ec/ET (**d**), Ei (**e**), Ei/ET (**f**), and ET (**g**) of high-hand barley at different altitude zones. The seasonal variations in ET components for highland barley were similar to that of other crops such as wheat, corn, and rice [9; 23; 48; 49]. For example, [PERSON] et al. [50] found that the ET components of spring maize presented a parabolic trend with the peak in the canopy-increasing stage in Loess Plateau in China. Four years of observations illustrated that ET, Ec, and Es showed similar seasonal variation patterns with the development of the canopy for maize in dry, semihumid climate regimes [14]. Both the observed and simulated ET exhibited similar temporal distributions for drylands in the arid regions of northwestern China [51]. The temporal distributions differed considerably among different ET component ratios. Ei/ET ratio (Figure 3f) generally presented a similar changing pattern to ET components. The Es/ET ratio (Figure 3b) increased progressively from the beginning of the year and reached the maximum in later April, and then it declined to the valley in the middle of August, and it subsequently increased, reaching the secondary maximum in early November, then it decreased till the end of the year. This was different from the result from [PERSON] et al. [28], who found that Es decreased with the increase in leaf area index (LAI) and time. The intra-annual variation in the Es/ET ratio was mainly related to the growing season of highland barley. From April to August, highland barley reaches its peak growth period. With the increase in vegetation canopy coverage, the shielding effect reduced the radiation energy reaching the surface, thus reducing the soil evaporation rate, and ultimately leading to the decrease in Es/ET. The Ec/ET ratio (Figure 3d) generally exhibited an opposite changing pattern to the Es/ET ratio, with two valleys corresponding to the two peaks of Es ratio, and a peak corresponding to the valley of Es ratio, which was consistent with the seasonal change in the Ec/ET ratio for dryland in northwestern China [51]. [PERSON] and [PERSON] [2] also found that the Ec/ET ratio did not vary significantly among the seasons for winter wheat in Beijing. The opposite trend between the season variation in Ec/ET and Es/ET ratios was also observed for maize in northwestern China [9]. Many studies reported different temporal distributions of the Ec/ET ratio of crops from that of highland barley in Tibet [14]. [PERSON] et al. [50] found that the Ec/ET ratio showed a parabolic trend for spring maize in the Loess Plateau. [PERSON] et al. [9] observed a strong seasonal pattern in the Ec/ET ratio, which increased continuously with the vegetation growth and then declined after grain filling for maize in northwestern China. A similar trend was also reported by [PERSON] et al. [24] for rice and corn in Tsukuba, Japan.