## 2 Materials and Methods
### Field Measurements  
Micrometeorological and biophysical data collected at each location as part of GRAPEX and T-REX are used to evaluate, validate, and refine ET estimates, detect crop stress, and monitor biomass development and root zone soil water availability. All sites are equipped with similar instrumentation, with measurements including surface energy balance flux estimates, turbulence and mean profile measurements of wind, temperature, and water  
Figure 1: Locations of each wine grape vineyard (GRAPEX; purple) and almond orchard (T-REX; brown) under study. Black lines are the boundaries of the field and purple or brown dots are tower locations. The latitude and longitude of each tower location are given after the abbreviated site name. vapor, as well as periodic ground-based biophysical measurements such as leaf-water potential, leaf area index (LAI), and gas exchange. Eddy covariance systems at the GRAPEX sites include a Campbell Scientific, Inc. integrated CO2 and H2O open-path gas analyzer and a three-dimensional ultrasonic anemometer collecting data at 20 Hz producing 30 min flux averages. Radiation is monitored via an NR01 four-component radiometer (Huuseflux, Delft, Netherlands), and humidity and temperature via an EE08 probe (E+E Elektronik, Engerwitzdorf, Austria) in a TS120 fan-aspirated shield (Apogee Instruments Inc., Logan, UT, USA). Ground heat flux is estimated through an array of soil heat flux plates (HFT-3, Radiation Energy Balance Systems, Bellevue, Washington) buried at a depth of roughly 8 cm, Hydraprobe soil moisture sensors (Stevens Water Monitoring Systems, Inc., Portland, OR, USA), and soil thermocouples for estimating heat storage above the plates (see [4; 6] for details of the eddy covariance and soil heat flux measurements). The eddy covariance flux systems at the T-REX sites include a similar instrumental setup with the exception of the radiation measurements monitored using a CNR4 net radiometer (Kipp and Zonen, Delft, the Netherlands). In order to further provide partitioned (separation of E and T) flux validation, we utilize a novel method based on quadrant analysis of high-frequency EC data, referred to as the conditional eddy covariance (CEC) approach [26]. The CEC approach is based on the similarity between stomatal (transpiration and photosynthesis) and non-stomatal (evaporation and respiration) pairs of component fluxes and works by combining measurements of high-frequency carbon dioxide and water vapor EC data to find all four component fluxes (transpiration, photosynthesis, evaporation, respiration) simultaneously. The CEC method is a simpler technique in comparison to other partitioning approaches (such as the modified relaxed eddy accumulation; MREA, flux-variance similarity; FVS) but circumvents the need to estimate water use efficiency (WUE) and gross primary product (GPP) as inputs. The approach has been applied in various systems, including forest, grassland, and vineyard sites [26]. Although the results were promising, particularly given the simplified approach, application within a vineyard site demonstrated some uncertainty worth mentioning. Most notable is the EC measurement height relative to the canopy height, where [26] suggests measurements be obtained as close as possible to the top of the canopy so air parcels emanating from the soil surface and canopy are not completely mixed. The EC tower height for the T-REX almond sites is roughly 5 m above the canopy, whereas the included GRAPEX vineyard sites are about 2.0 to 2.5 m above the canopy. Heights were chosen to include fetch and footprint requirements so ET observations could provide validation to remotely sensed values. Although the distance from the canopy is not ideal, we assume the CEC technique gives reasonable partitioning estimates but acknowledge potential deficiencies in the values. To conduct a reliable and consistent comparison between daily observed measurements and modeled flux estimates, which assume closure on a daily scale, we use a closure approach offered in [7].