## 3 Results
### Evaporation and Transpiration Partitioning
Such a result is expected as RIP and VAC are most prone to advective conditions. Focusing on VAC for days with high ET (\(\geq\)4 mm day\({}^{-1}\); Landsat overpass dates of 9 June, 25 June, and 11 July 2021) shows nearly identical total ET estimates for DisALEXI-PT and DisALEXI-PM. However, DisALEXI-PT suggests T/ET ratios close to ~0.5, meaning E is contributing ~50% to total water use during this time period. This amount of E is not likely to occur given the dry barren interrow present during the summer at VAC. Conversely, DisALEXI-PM suggests T/ET ratios closer to 1.0. This same pattern, albeit less drastic, is seen at RIP, where the DisALEXI-PT T values show negative bias with the CEC T for values \(\geq\) 4 mm day\({}^{-1}\), while the DisALEXI-PM T shows better alignment for the same values. At site OLA, we find DisALEXI-PM overestimates T (aligning with CEC E) and DisALEXI-PT overestimates E (aligning with CEC T), contributing to both estimating similar total ET estimates (Figure 5). Figure 4: Time series of DisALEXI-PT-derived E and T ((**left**) brown and green bars, respectively) and DisALEXI-PM-derived E and T ((**right**) brown and green bars, respectively) on clear Landsat 8 overpass dates during 2021. Additionally included are CEC-derived daily estimated E and T (brown and green lines, respectively) and daily LAI (blue line). As described in Section 2.3.2, a major difference between DisALEXI-PT and DisALEXI-PM is how the \(\mathrm{T_{c}}\) at the satellite overpass time is calculated when solving the temperature gradient-resistance system of the equations. Therefore, differences in E or T from DisALEXI-PT or DisALEXI-PM propagate from estimates of \(\mathrm{T_{c}}\). Additionally, past research has shown that the effect advection, and by proxy, VPD, can have on estimates of T [33; 43]. Figure 6 compares the DisALEXI-PT and DisALEXI-PM \(\mathrm{T_{c}}\) estimates with \(\mathrm{T_{a}}\) (initial estimate used as model input) and VPD (calculated using \(\mathrm{T_{a}}\) and CFSR vapor pressure). The results suggest a common trend, with \(\mathrm{T_{c}}\) (y-axis) and VPD (color scale) increasing with an increase in \(\mathrm{T_{a}}\) for all sites and both approaches (Figure 6A,B). In both models, \(\mathrm{T_{c}}\) follows a linear correlation with \(\mathrm{T_{a}}\), with values between 0 to \(\sim\)2 \({}^{\circ}\)C warmer than \(\mathrm{T_{a}}\) throughout most of the year and regardless of site. However, there are specific instances when \(\mathrm{T_{c}}\) is reported as less than \(\mathrm{T_{a}}\), a characteristic of dry air advection. These instances are only identified in DisALEXI-PM-derived \(\mathrm{T_{c}}\) values (Figure 6B); the DisALEXI-PT \(\mathrm{T_{c}}\) estimates always remain \(\geq\)\(\mathrm{T_{a}}\) (Figure 6A). Instances of \(\mathrm{T_{c}}\leq\mathrm{T_{a}}\) tend to align with higher VPD (red tones), with more occurrences at higher \(\mathrm{T_{a}}\) values. However, there are instances when \(\mathrm{T_{c}}\leq\mathrm{T_{a}}\) even at cooler temperatures (\(\mathrm{T_{a}}\leq 25\) \({}^{\circ}\)C). Closer inspection indicates a division between \(\mathrm{T_{c}}\) and VPD for instances of \(\mathrm{T_{c}}\leq\mathrm{T_{a}}\) (Figure 6C, red) and \(\mathrm{T_{c}}\geq\mathrm{T_{a}}\) (DisALEXI-PM = blue, DisALEXI-PT = green; Figure 6C). This is because DisALEXI-PM accounts for the effects of elevated VPD via its explicit inclusion within the framework (see Equation (10)), whereas DisALEXI-PT assumes that the influence of VPD is mostly accounted for in the \(\alpha\) parameter. Most instances of \(\mathrm{T_{c}}\leq\mathrm{T_{a}}\) link to the large differences in the DisALEXI-PT and DisALEXI-PM T estimates discussed above and shown in Figure 6. Specifically, the improvement in T estimation by DisALEXI-PM compared to DisALEXI-PT for RIP and VAC for values \(\geq 4\) mm day\({}^{-1}\) align with instances of \(\mathrm{T_{c}}<\mathrm{T_{a}}\) (not shown), suggesting the improvement in these cases is related to VPD inclusion.