The vertical turbulent structure within the surface boundary layer above vineyards in California’s Central Valley during GRAPEX

Authors: Alfieri, Joseph; Prueger, John; Kustas, William - Bill; HIPPS, L. - Utah State University; BAMBACH, N. - Uc Davis Medical Center; McKee, Lynn

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2022
Publication Date: 3/5/2022
Citation: Alfieri, J.G., Prueger, J.H., Kustas, W.P., Hipps, L.E., Bambach, N., Mckee, L.G. 2022. The vertical turbulent structure within the surface boundary layer above vineyards in California’s Central Valley during GRAPEX. Irrigation Science. https://doi.org/10.1007/s00271-022-00779-x.
DOI: https://doi.org/10.1007/s00271-022-00779-x

Interpretive Summary: Improving irrigation management is critical to ensuring water, already a scare resource in California, is used effectively. But managing irrigation in vineyard is complicated by their unique canopy structure. Because of the wide rows and clumped natures of the vines, current theories and the models that rely on them may not adequately describe the physical processes controlling water loss from vineyards. By applying spectral analysis techniques to data collected as a part of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX), this study characterized the vertical turbulent structure over a vineyard in the Central Valley of California. The result suggests the direction of air flow can strongly influence the vertical turbulent structure above the vines and thus the exchange of heat and moisture. The direction of air flow, which is not considered by current modeling methods, may prove to be an important factor for accurately modeling vine water loss and irrigation needs.

Technical Abstract: Water is already limited resource is California and meeting the competing water needs there will only be more challenging in the coming decades. Thus, sustaining the production of wine grapes, which are among the highest value specialty crops in the state, requires water is used efficiently as possible. At the same time, improving irrigation management in vineyards requires spatially distributed information regarding vine water needs at the sub-field scale that can only be collected via remote sensing. However, due to their unique canopy structure, current remote sensing models may not accurately describe the underlying turbulent flow controlling evapotranspiration from vineyards. To address that knowledge gap, this study investigates the vertical turbulent structure over a vineyard in the Central Valley of California. Using data from an wind velocity profile (2.5 m, 3.75 m, 5 m, and 8 m) collected during 2017 as a part of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX), this study characterized the relationship between the turbulent flow at different heights using spectral analysis. It was found that the turbulent structure for the horizontal wind velocity components was strongly related for large (lower frequencies) turbulent eddies and become increasingly decoupled as the eddy size decreases until the correlation falls to zero when the eddy size is smaller than the separation distance between measurements. As a result, the overall correlation (covariance) decreases following a well-defined logarithmic relationship with separation distance. Moreover, because of the canopy structure of vineyards, airflow perpendicular to the vines interacts more with canopy than airflow parallel to the vines and as a result the strength of the correlation decreases more rapidly. This result suggest wind direction can influence the vertical turbulent structure above the vines and thus the turbulent exchange of heat and moisture. This dependency on wind direction is a unique characteristic of highly structured canopies that may prove important to accurately modeling vine water loss and irrigation needs.