# Evapotranspiration in Dynamic of Highland Barley Using PML ET Product in Tibet
## 4 Conclusions  
This study investigated the characteristics and variations in ET components and their proportions of highland barley in Tibet using the PML ET product during 2001-2020 and explored the relations between the variation in ET components and meteorological factors. The results showed that Es was the most predominant ET component and accounted for 77.3% of the total ET of highland barley in Tibet. ET components varied obviously over the altitude; ET generally decreased with the increase in altitude, with higher ET observed at 3700-3800 m altitude zone. Es and the Es/ET ratio showed a decreasing trend with the increase in altitude from 3500 m to 3800 m and then changed to an increasing trend until reaching the altitude of 4100 m, while Ec, Ei and their ratios presented an opposite varying pattern to ES. Seasonal variations in daily ET components of highland barley displayed a parabolic pattern peaked in August, while the temporal distributions differed considerably among different ET component ratios. The Ei/ET ratio generally presented a similar changing pattern to ET components. The Es/ET ratio showed a dual parabolic pattern with two peaks in April and November and a valley in August, while the Ec/ET ratio generally exhibited an opposite changing pattern to the Es/ET ratio. Seasonal variations in ET components were greatly affected by meteorological variables. ET components were correlated significantly with air temperature, relative humidity, and precipitation, while the seasonal variations in Es/ET and Ec/ET ratios were more influenced by the environment (such as sowing time, highland barley varieties), irrigation practices, and management rather than meteorological variables. Es and its ratio in highland barley decreased significantly during 2001-2020, while the Ec/ET ratio \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Meteorological** & & & & & & & \\
**Variables** & **Es** & **Ec** & **Ei** & **ET** & **Es/ET** & **Ec/ET** & **Ei/ET** \\ \hline SD & 0.415 & 0.196 & 0.056 & 0.460 & 0.203 & \(-\)0.193 & \(-\)0.263 \\ AP & 0.042 & \(-\)0.182 & 0.125 & 0.000 & 0.098 & \(-\)0.110 & 0.122 \\ T & 0.078 & \(-\)0.067 & 0.048 & 0.062 & 0.089 & \(-\)0.092 & \(-\)0.006 \\ WV & 0.183 & 0.158 & \(-\)0.080 & 0.218 & 0.058 & \(-\)0.046 & \(-\)0.211 \\ RH & \(-\)0.040 & \(-\)0.304 & 0.503 & \(-\)0.102 & 0.159 & \(-\)0.199 & 0.507 \\ P & \(-\)0.239 & \(-\)0.153 & 0.432 & \(-\)0.267 & \(-\)0.099 & 0.069 & 0.609 \({}^{*}\) \\ \hline \hline \end{tabular}  
* Significant at 0.05 significance level.  
\end{table} 
Table 3: Correlation coefficients between the interannual variations in ET components and meteorological variables. generally showed an opposite trend to the Es/ET ratio; Ei and its ratio presented an insignificantly decreasing trend. The interannual variations in ET components were not significantly correlated significantly with meteorological variables, while the Ei was more influenced by meteorological variables, especially precipitation characteristics. Conceptualization, visualization, and writing--original draft preparation, J.C.; funding acquisition, review, and validation, H.T. ; conceptualization, validation, and writing--review and editing, Y.J. ; software, methodology, Q.T. ; formal analysis, L.Y. ; review and validation, Q.C. ; review, supervision, funding acquisition, and writing--review and editing, D.T. All authors have read and agreed to the published version of the manuscript. This research was funded by the Youth Innovation Promotion Association (No. 2018417 and 2021385), the National Natural Science Foundation of China (No. 41901130 and 42061015), Chongqing Science and Technology project (No. cstc2021 jcyj-msxmX0187), Chongqing Municipal Bureau of Water Resources (No. 5000002021 BF40001), Institute of Agricultural Resources and Environment, Tibet Academy of Agricultural and Animal Husbandry Science (No. 2020 ZZKT-01), and Rikaze City Science and Technology Plan Project (No. RKZ2020 KJ01).