TO: Technical Advisory Group for the Napa County Groundwater Sustainability Agency
FROM: Brian D. Bordona, Director of Planning, Building and Environmental Services
REPORT BY: Jamison Crosby, Natural Resources Conservation Manager
SUBJECT: Presentation on GRAPEX Project and Application of Multi-Scale Remote Sensing Evapotranspiration Toolkit for Mapping Crop Water Use and Crop Stress for Improved Irrigation
RECOMMENDATION
title
The TAG will receive an update on the use of satellite and land-based remote sensing data for analysis of evapotranspiration and information that can be used to refine vineyard water use estimates for Napa Valley Subbasin integrated hydrologic modeling purposes.
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Procedure
Staff introduces.
Questions and answers with the TAG.
Public comments.
BACKGROUND AND DISCUSSION
Remotely-sensed evapotranspiration (ET) estimates informed the development of the Napa Valley Integrated Hydrologic Model (NVIHM) for the Groundwater Sustainability Plan (GSP). These estimates used data from 2014 to develop crop coefficients for black and white grapes in Napa Valley. As previously presented to the TAG, the total water use, as measured by ET, varies across the Napa Valley Subbasin. The initial crop coefficients developed during GSP development provided the foundation for determining applied water requirements, for both surface and groundwater, for irrigated acreages within the NVIHM. Refining the estimates of applied water is a priority during GSP implementation. Since the initial NVIHM development, multiple data sources, including local sensors as well as remotely sensed data, are being used to update modeled ET.
Field measurements of ET using surface renewal methods by Tule Technologies were presented at the October 2022 TAG meeting. The measured data provides daily, field-scale measurements of ET. As previously discussed with the TAG, the use of local data is necessary to refine crop coefficients in Napa County. An overview of remotely sensed ET measurement technologies, OpenET, was presented at the November 2022 TAG meeting. OpenET is an online platform that uses the best available science and publicly available data to provide satellite-based ET estimates. OpenET has been used in multiple applications across the Western US as well as for multiple Groundwater Sustainability Agencies (GSA) within California.
Outreach to Napa County vineyard managers and other users of Tule Technologies sensors began in Spring 2023 led by the Napa County Resource Conservation District (RCD). To date, data from 17 volunteered sensors have been obtained from the region. A comparison of field-measured ET with remotely-sensed ET is being conducted at these locations.
Extensive analyses of remotely-sensed data and the development of tools to support vineyard water management have been underway for over a decade as the core mission of GRAPEX (Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment). GRAPEX is a highly collaborative and interdisciplinary experiment, which involves USDA-Agricultural Research Service (ARS) scientists, industry, and university researchers. The large scope of GRAPEX research has allowed the development of new measurement and remote sensing tools and techniques to quantify vine evapotranspiration, moisture status, and stress, with the goal of improving precision irrigation management in California vineyards.
Through the support of a NASA Applied Sciences grant as well as continued support from USDA and grower partners, GRAPEX validation sites have expanded and include the coastal growing region in Sonoma County and Madera/Fresno Counties. This expansion resulted in a significant north-south climate gradient, different vine varieties, soil properties, topography, trellis systems, canopy size, water requirements, and management practices. GRAPEX efforts combine in-situ and remotely-sensed data to investigate the effects of canopy structure and row orientation on energy and moisture exchange processes within and above the vine canopy. A critical component of GRAPEX has been to work closely and collaboratively with scientists at commercial partners to ensure that both the experimental data being collected and the models and tools being developed can address critical operational needs.
Andrew McElrone, a Research Plant Physiologist with USDA-ARS, an Adjunct Professor in the Department of Viticulture and Enology at UC Davis, and collaborator and co-lead on the GRAPEX research, will provide a presentation to the TAG on GRAPEX findings to date, continuing research efforts, and opportunities to coordinate with the GSP team to utilize remotely-sensed and ground-based data to enhance crop water use estimates represented in NVIHM.
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: The proposed action is not a project as defined by 14 California Code of Regulations 15378 (State CEQA Guidelines) and therefore CEQA is not applicable.
SUPPORTING DOCUMENTS
A. Presentation on GRAPEX Project and Application of Multi-Scale Remote Sensing Evapotranspiration Toolkit for Mapping Crop Water Use and Crop Stress for Improved Irrigation Scheduling and Water Management in Vineyards (Andrew McElrone, December 2025)