## 3 Results  
### Evaluation of ALEXI/DisALEXI ET  
The ALEXI/DisALEXI modeling scheme has been previously evaluated in California vineyards as part of the GRAPEX project, with resulting daily ET fluxes comparing well with observations (RMSE <= 1.0 mm day\({}^{-1}\); [15; 16; 17; 19; 58; 59; 60]). In the current study, we focus on three GRAPEX vineyard sites: BAR, SLM, and RIP. These individual sites were chosen because of their differing cultivars and locations that span the state, offering maximum diversity when making comparisons [6]. The almond orchards used for validation in the current study are VAC, WWF, and OLA and are part of the T-REX project as described in Section 2.1. Although many years of observed data exist at the proposed GRAPEX sites, we focus on 2021 as it overlaps with the availability of observations at the T-REX locations, providing uniformity in what otherwise might be differences in meteorological conditions year to year. Figure 2 shows the resulting ALEXI/DisALEXI ET values for the Priestley-Taylor-based approach (DisALEXI-PT) and the Penman-Monteith-based approach (DisALEXI-PM) compared against observations for all sites on clear Landsat 8 overpass dates. Vineyard sites are on the top (purple) and almond sites are on the bottom (brown). Observations are taken as the average of multiple energy balance closure techniques as described in [7] and Section 2.2. Unclosed ET observations versus DisALEXI-PT and DisALEXI-PM ET are also shown (Figure 3). The results show good agreement between modeled and closed observed estimates, with an average Root Mean Square Error (rmse) of 1.10 mm day\({}^{-1}\) for DisALEXI-PT and 1.14 mm day\({}^{-1}\) for DisALEXI-PM on Landsat overpass dates. Although DisALEXI-PT performs slightly better at all sites, small differences in total ET are found between the approaches, regardless of crop or location. The largest errors are reported at sites OLA and RIP, the two southernmost sites. At RIP, errors are due to deviations between the modeled and observed estimates at high values of ET (Figure 2), while a consistent positive bias error is present at OLA. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**SITE** & **CROP** & **Landsat-8 Scene** & **HLS Scene** & **Clear Image Days** \\ \hline BAR & Vineyard & p045-r033 & T10 SEH & 13 \\ \hline VAC & Almond & p044-r033 & T10 SEH & 12 \\ \hline WWF & Almond & p044-r033 & T10 SEH & 12 \\ \hline SLM & Vineyard & p044-r033/p043-r034 & T10 SFH & 26 \\ \hline RIP & Vineyard & p043-r034/p042-r035 & T11 SKA & 30 \\ \hline OLA & Almond & p043-r034/p042-r035 & T11 SKA & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Landsat 8 Collection 2 and HLS scenes used for each site. Additionally included are the number of images used for each site during the period of study (2021). Note more clear image days for sites with overlapping Landsat scenes. Figure 3: Scatter plots of DisALEXI-PT- and DisALEXI-PM-derived daily ET vs. observed daily ET (unclosed) for GRAPEX vineyards (**top**) and T-REX almond orchards (**bottom**) on clear Landsat 8 overpass dates during 2021. Additionally, included are statistical measures n (number of clear-sky images available), r2 (coefficient of determination), rmse (Root Mean Square Error), and mbe (Mean Bias Error). Differences between the number of comparison points (n) and the number of clear-sky days (Table 1) are due to missing observed data during the Landsat overpass. Figure 2: Scatter plots of DisALEXI-PT- and DisALEXI-PM-derived daily ET vs. observed daily ET (closed via [7]) for GRAPEX vineyards (**top**) and T-REX almond orchards (**bottom**) on clear Landsat 8 overpass dates during 2021. Additionally included are statistical measures n (number of clear-sky images available), r2 (coefficient of determination), rmse (root mean square error), and mbe (mean bias error). Differences between the number of comparison points (n) and the number of clear-sky days (Table 1) are due to missing observed data during the Landsat overpass.