Monitoring Water Use and Stress with Evapotranspiration Estimates Derived Using Thermal-Based Satellite Remote Sensing in California Vineyards

Irrigation in the central valley of California is essential for successful wine grape production, which represents nearly 1 million acres values at approximately 6 billion dollars. With reductions in water availability and competing water use interest in much of California, there is a critical need in optimizing water management strategies to preserve water resources and maintain sustainable wine grape production. In the current study, we investigate the utility of satellite-derived maps of evapotranspiration (ET) based on remotely sensed land surface temperature (LST) imagery as a useful tool to determine crop water use and stress. Specifically, we evaluate a two-source (soil/substrate + vegetation) remote sensing-based ET modeling approach over two Pinot noir vineyard sites being monitored as part of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX). The Disaggregated Atmosphere Land EXchange Inverse (ALEXI/DisALEXI) modeling system provides ET estimates with both high spatial (30m) and temporal (daily timesteps) resolution by fusing LST data from multiple satellite platforms. Surface energy balance/ET and biophysical data collected from each vineyard between years 2013 and 2016 are used to evaluate model performance. Estimates of daily ET derived using ALEXI/DisALEXI agree reasonably well with ground-based flux estimates, with slight negative biases reported during the early spring season. Spatial analysis indicates heterogeneity in ET within each relatively small vineyard, indicating point-based ET estimates used to represent the entire vineyard may limit the effective use of irrigation water. Overall, the ALEXI/DisALEXI/Fusion modeling approach described here can provide reliable information regarding the monitoring of evaporative water loss and crop stress at the field and regional scale; aiding irrigation managers in regions with competing demands for limited water resources. Comparisons to currently applied operational ET estimation methodologies, such as the crop coefficient based estimation of crop ET and the Mapping Evapotranspiration with Internalized Calibration (METRIC) modeling approach will also be presented. Evaluation of the ALEXI/DisALEXI daily ET product is expanding over other vine varieties and climates in California and we are exploring ways to use this information in supporting operational water management decisions in vineyards.