Mapping Daily Evapotranspiration over California Vineyards of Different Climate and Vine Variety Using the ALEXI/DisALEXI Fusion Model Approach

Mapping the spatial variability of actual evapotranspiration (ET) across vineyards is necessary for optimizing irrigation scheduling and efficiency, subsequently leading to the conservation of water resources and maintaining sustainable wine grape production. In the current study, we utilize thermal-based satellite remote sensing data from multiple platforms to derive maps of ET. We combine the Disaggregated Atmosphere Land Exchange Inverse (ALEXI/DisALEXI) surface energy balance model and the Spatial Temporal Adaptive Reflectance Fusion Model (STARFM) to generate ET estimates at high spatial (30m) and temporal (daily) resolution. Model output is evaluated for year 2017 over vineyard sites located in Sonoma, Sacramento and Madera counties in California that are being monitored as part of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX). Each vineyard is planted with a different vine variety and grown for distinct purposes, such as yield or quality. Additionally, these vineyards span a climate gradient from generally cooler/wetter to hotter/drier from north to south and consequently lower to higher evaporative demand trends throughout the day and year. Comparisons with micrometeorological data indicate reasonable model performance at all sites, with mean absolute errors and bias similar to past GRAPEX studies. Trends across the three domains indicate advection remains an issue at sites located in the California Central Valley, causing underestimation of modeled ET during peak growing season. These results corroborate previously presented results from GRAPEX studies and is the topic of current research aimed at addressing this issue. Spatiotemporal analyses illustrate the ability of ALEXI/DisALEXI/data fusion package to characterize heterogeneity in ET both within a vineyard and over the surrounding landscape. These findings will inform the development of strategies for integrating ET mapping time series into operational irrigation management framework, providing actionable information regarding vineyard water use and crop stress at the field and regional scale and at daily to multi-annual timescales.