Coherent Interactions of Turbulence and Microclimate in Irrigated Vineyards

Water use by irrigated vineyards is a critical issue given that cultivation of wine grapes is worldwide with over 7 million hectares of vineyards distributed over 100 countries on six continents. . Uncertainty regarding the availability of water resource in the future demands better knowledge, models, and measurements for both evapotranspiration (ET) from vineyards and the environmental conditions controlling them. The GRAPEX project has integrated remote sensing models for ET, eddy covariance measurements of energy balance, and other physical and physiological observations in irrigated vineyards in California. The microclimate in the vineyard canopy represents the actual environment in which the grapes grow. Also, the complex interactions between the microclimate and air above the canopy is a key mechanism regulating ET. Modern micrometeorological technology offers the ability to examine episodic variations of properties of air in the canopy and the connections with turbulence transport. Our goal is to quantify the characteristics of turbulence, temperature, and humidity in the canopy, and how they are linked with the properties of the air above the vines. The hypothesis addressed is that the properties in the canopy will exhibit episodic variations due to periodic coherent turbulence exchange between the canopy and air aloft.Eddy covariance systems were installed above and within an irrigated vineyard, measuring at the same time three components of wind, temperature, and the water vapor density. This allows examination of the linkages between variations in microclimate with transient turbulence exchanges within and above the vines. Results show large differences in humidity exist between the above, inter-row and within row locations. The mean values of temperature and humidity do not reflect the episodic nature of air temperature and humidity, especially inside the canopy. The probability distribution of contiguous periods exceeding various humidity thresholds; the intermittency of temperature and humidity; and the scales and intensities of turbulence above the vines that couple with changes within the canopy were also examined. The results demonstrate the nature of vine microclimate and its interactions with the regional advection of hot and dry air.