The Oasis-Desert Effect (OAE) may significantly impact crop water use in irrigated fields under extremely arid conditions. Wine-grape production from vineyards can be found in multiple regions where the natural arid landscape is drastically modified through irrigation to optimize yield and fruit quality. Evapotranspiration (ET) fluxes derived through the eddy covariance (EC) technique, in an ideal case, are considered a direct measurement of crop water use. The Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project has collected EC data over a dozen California commercial vineyards. These vineyards encompassed a wide range of climatic conditions, vine varieties, soil characteristics, and management and production goals. The OAE is linked to an ET increase due to the energy contribution from the horizontal flow of dry, hot air into irrigated cropland, which leads to a significant evaporative cooling. Unfortunately, the energy contribution from horizontal advection violates the EC assumption of stationary flows. Thus, a quantitative understanding of horizontal advection influence over irrigated crops in drylands requires exploring novel micrometeorological approaches beyond the EC technique. We propose that these advective conditions do not follow classic stable conditions where turbulence is suppressed/weak as the turbulent transport of water vapor is significantly enhanced. We have found that days of strong Oasis-Desert advective conditions can increase crop water use by up to 50% compared to assuming that ET enhancement due to horizontal advection is negligible. We highlight the importance of recognizing the limitation of standard micrometeorological techniques to quantify ET for model validation and field-scale monitoring.
Dr. Nicolas Bambach
The Vineyard-Oasis-Desert Advective Effect on Evapotranspiration and Irrigation Management: Lessons from the GRAPEX Project
University of California, Davis, USA