Observations from Leaf and Canopy to Field, Landscape and Regional Scales for Understanding Soil-Plant-Atmosphere Exchange Processes Influencing Evapotranspiration in Vineyards

Wine grapes are grown on 6 of the 7 continents with most grown in arid and semi-arid regions which are being affected by more frequent and severe droughts and heat waves due to climate change. The GRAPEX (Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment) project was designed to collect observations across a broad range of spatial and temporal scales in order to understand and develop models using remote sensing for accurately quantifying actual vine water use (Evapotranspiration, ET) and vine water status. This information is critical to improve water use efficiency and conserve water though improved deficit irrigation practices. To understand and develop models of the soil-plant-atmosphere exchange processes of vineyard systems requires an interdisciplinary approach involving plant physiology, soil physics, micrometeorology, biometeorology, hydrology, atmospheric science just to name a few. Modeling water, energy and carbon exchange from vineyards is challenging due to the significant interrow spacing relative to plant height and a managed canopy architecture leading to strongly clumped vegetation with non-uniform vertical distribution of biomass. Moreover, in these irrigated environments, local and regional scale advection affects both the measurement and modeling of fluxes and complicates the interpretation of the results. The observations made during GRAPEX Intensive Observation Periods (IOPs) included leaf-scale gas exchange, water potential and hyperspectral measurements, micrometeorological measurements of energy exchange above and below the vine canopy and in the interrow, biomass and leaf area measurements and soil moisture profile measurements together with tower-based, aircraft and satellite remote sensing data. An overview of the key findings from GRAPEX will be presented on understanding soil-vine-atmosphere turbulent exchange processes and efforts in the development of a remote sensing-based ET modeling system adapted to provide reliable ET for improving irrigation scheduling and water conservation.