Intermittency of water vapor fluxes from vineyards during light wind and convective conditions
- 16 Downloads
Vineyards in many semi-arid regions globally face limited water resources. Monitoring evapotranspiration (ET) of vineyards is critical for water resource management, but remains difficult due to the complex biophysics of the surfaces. Both measurement and modeling approaches for estimating turbulent water vapor transport rely on implicit assumptions that exchanges occur in a reasonably regular fashion over the time scales generally used for averaging. However, heterogeneous vegetation in semi-arid climates, such as many vineyards, presents inherent factors, including canopy row/row space structure and frequent periods of light wind, unstable conditions, that can create episodic transport characteristics. Eddy covariance data were collected above and within the canopy of two vineyards in the Central Valley of California during the Grape Remote sensing Atmospheric Profile & Evapotranspiration eXperiment (GRAPEX). The goal was to document and quantify the existence of intermittent turbulence transport of water vapor, and associated episodic canopy venting. These effects were found to correlate with periods light winds and highly unstable/convective conditions. Power and cross-spectra for intermittent periods documented enhancement of low-frequency water vapor exchange events compared to more steady periods, and diminished time scale correlation between humidity within the canopy and above the canopy. Analyses show that intermittent cases can necessitate longer flux-averaging periods (up to 2 h) than more steady conditions. Episodic exchange events were isolated and summed to determine their relative contribution to the overall water vapor flux. Since light wind, unstable conditions are relatively common in many arid vineyard regions, these findings have implications for mechanistic ET models that rely on time-averaged vertical gradients, which implies reasonably steady transport.
Funding was provided by Utah Agriculture Experiment Station Project UTAO 1186 and NASA Grant #NNX17AF51G. Much of the data collection during GRAPEX IOPs was made possible through funding provided by E.&J. Gallo Winery. In addition, we would like to thank the staff of the Viticulture, Chemistry and Enology Division of E.&J. Gallo Winery for their logistical support as part of the GRAPEX project. Finally, this effort would not have been possible without the cooperation of Mr. Ernie Dosio of Pacific Agri Lands Management, along with the Borden vineyard staff, for logistical support of GRAPEX field and research activities. USDA is an equal opportunity provider and employer.
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
- Alfieri JG, Kustas WP, Nieto H, Prueger JH, Hipps LE, McKee LG, Gao F, Los S (2018) Influence of wind direction on the effective surface roughness of vineyards. Irrigation Sci (this issue) Google Scholar
- Campbell GS, Norman JM (1998) Heat flow in the soil. In: An introduction to environmental physics. Springer, New YorkGoogle Scholar
- Kustas WP, Anderson MC, Alfieri JG, Knipper K, Torres-Rua A, Parry CK, Nieto H, Agam N, White WA, Gao F, McKee L, Prueger JH, Hipps LE, Los S, Alsina MM, Sanchez L, Sams B, Dokoozlian N, McKee M, Jones S, McElrone A, Heitman JL, Howard AM, Post K, Melton F, Hain C (2018) The grape remote sensing atmospheric profile and evapotranspiration experiment. Bull Am Meteor Soc 99:1791–1812CrossRefGoogle Scholar
- Lee Y-H (2011) Intermittency of turbulence within open canopies. J Atmos Sci 47:2:137–149Google Scholar
- Peixoto JP, Oort AH (1992) Physics of climate. American Institute of PhysicsGoogle Scholar
- Robinson J (ed) (2006) The oxford companion to wine (3rd ed.) Oxford University PressGoogle Scholar
- Semmens KA, Anderson MC, Kustas WP, Gao F, Alfieri JG, McKee LG, Prueger JH, Hain CR, Cammalleri C, Yang Y, Xia T, Sanchez L, Alsina M, Velez M (2016) Monitoring daily evapotranspiration over two California vineyards using Landsat 8 in a multi-sensor data fusion approach. Remote Sens Environ 185:155–170CrossRefGoogle Scholar
- Vassilicos JC (2010) Intermittency in turbulent flows. Cambridge University Press, CambridgeGoogle Scholar