A multi-year intercomparison of micrometeorological observations at adjacent vineyards in California’s Central Valley during GRAPEX

Authors: Alfieri, Joseph; Kustas, William - Bill; Prueger, John; McKee, Lynn; HIPPS, L.E. - Utah State University; Gao, Feng

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2018
Publication Date: 10/20/2018
Citation: Alfieri, J.G., Kustas, W.P., Prueger, J.H., McKee, L.G., Hipps, L., Gao, F.N. 2018. A multi-year intercomparison of micrometeorological observations at adjacent vineyards in California’s Central Valley during GRAPEX. Irrigation Science. 37(3):345-357. https://doi.org/10.1007/s00271-018-0599-3.
DOI: https://doi.org/10.1007/s00271-018-0599-3

Interpretive Summary: California is among the largest wine-producing regions in the world. It is also a region with limited water resources. To ensure that scarce water resources are used effectively and ensure the long-term sustainability of the wine industry there, the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project was initiated to develop remote sensing-based tools that are able to monitor evapotranspiration from vineyards and inform irrigation management decisions. This study uses data from GRAPEX to compare the surface fluxes from a pair of adjacent vineyards in order to better understand the role of environmental conditions in controlling evapotranspiration. While there were no statistically meaningful differences in the meteorological conditions, such as wind speed, air temperature, and humidity, there were large inter-site and inter-annual differences in the surface fluxes at the two vineyards. It was found that the differences in the fluxes could be largely explained by differences in vegetation density and soil moisture. Since these quantities are, in turn, dependent on vineyard management practices, this work highlights the importance of management decisions for ensuring limited water resources are used effectively.

Technical Abstract: California is among the largest wine-producing regions in the world. It is also a region with limited water resources. To ensure that scarce water resources are used effectively, the ongoing Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project seeks to improve irrigation management within vineyards by providing remote sensing-based tools that can monitor ET across the continuum from sub-vineyard to regional scales. This study, which was conducted as a part of the GRAPEX project, compares the surface fluxes collected over a pair of vineyards separated by approximately 1 km from 2013 to 2017 to better understand the role of environmental conditions in controlling evapotranspiration. A comparison of the meteorological conditions, which include wind speed, wind direction, air temperature, water vapor pressure, and atmospheric pressure, showed there was no statistically meaningful difference in the measurements of these quantities either between the two vineyards or year-to-year. In contrast, the comparison of the surface fluxes, and in particular the sensible heat (H) and latent heat ('E) fluxes, showed there were large inter-site and inter-annual differences. On average, during the growing seasons, H differed by 28 W m-2 while 'E differed by 32 W m-2. With coefficients of determination (r2) in excess of 0.90, the differences in the surface fluxes can be largely explained by differences in leaf area index (LAI) and soil moisture content. Since these quantities are, in turn, dependent on vineyard management practices, this work highlights the importance of management decisions for ensuring limited water resources are used effectively.