# Evapotranspiration in Dynamic of Highland Barley Using PML ET Product in Tibet
## 3 Results and Discussion
### Seasonal Variations in ET Components
ET components were greatly affected by meteorological variables; the correlation coefficients between the seasonal variation in ET components and meteorological variables are listed in Table 2. ET components were positively correlated significantly with air temperature (\(p<0.01\)), relative humidity (\(p<0.01\)), and precipitation (\(p<0.01\)). ET and Es had the strongest correlations with air temperature, followed by relative humidity and precipitation. Previous studies showed that the meteorological variables had an important effect on seasonal variations in ET components [5; 23; 52; 53]. Moreover, Ec and Es were greatly affected by soil moisture [2; 54]; higher relative humidity and precipitation can increase the availability of soil moisture, which can promote the process of soil evaporation and vegetation transpiration [55]. Observation showed that the Ec rate had a linear relationship with air temperature for maize in arid regions [23; 56]. The significant influence of air temperature on Ec was also reported by [PERSON] et al. [57] and [PERSON] et al. [58]. These results were consistent with the strong correlations between Ec, Es, and air temperature, relative humidity, and precipitation. Ei correlated most significantly with relative humidity (\(p<0.01\)) and precipitation (\(p<0.01\)). The result agreed well with that from [PERSON] et al. [9] who found that Ei increased with the increase in precipitation for maize in northwestern China. Previous studies showed that Ei increased slowly with the increase in precipitation, while it gradually stabilized at maximum evaporation from the canopy, conforming well to a power function relationship [59; 60]. However, the ratio of Ei to the gross precipitation decreased with the increase in precipitation, generally implying that higher Ei would occur during small precipitation yet with a longer duration [30]. ET components were negatively correlated with sunshine duration, while they correlated poorly with water vapor. Es/ET and Ec/ET ratios were not correlated with all the meteorological variables (Table 2), generally indicating that their seasonal variations were affected by the environment (such as sowing time, highland barley varieties), irrigation practice, and management rather than meteorological variables, which was reported by many studies [24; 61]. For example, [PERSON] and [PERSON] [2] revealed that seasonal changes in the Ec/ET ratio could be well described as a function of LAI for winter wheat in Beijing, implying that crop development plays a critical role in allocating the ET components. [PERSON] et al. [44] also found a stronger correlation between the LAI and Ec/ET ratio of winter wheat. It is commonly reported that Es/ET and Ec/ET ratios varied exponentially and logarithmically with the increase in LAI for most crops, respectively [2; 62; 63]. This relationship was confirmed by many observations at field scale and model simulations at regional scales [24; 41; 46; 64], while Ei/ET ratio correlated most significantly with relative humidity (\(p<0.01\)), followed by precipitation (\(p<0.01\)), air temperature (\(p<0.01\)), and sunshine duration (\(p<0.01\)).