How Well Does the Two-Source Energy Balance Model Partition ET in a Drip-Irrigated Vineyard?.

The Two-Source Energy Balance model (TSEB) estimates evapotranspiration (ET) by separately computing vegetation and soil energy fluxes using a system of temperature differences and resistance formulations, where soil and canopy temperatures are derived from the composite surface temperature and the fraction vegetation cover. TSEB has been shown to accurately estimate ET over various agricultural crops and under a wide range of environmental conditions, but validation of the separate components, evaporation from the soil (E) and canopy transpiration (T) has only been conducted in irrigated corn and cotton fields.  In this study, TSEB was evaluated and adapted for independent E and T estimations in an isolated drip-irrigated wine-grape vineyard in the arid Negev desert.

Data were collected in the vineyard over the growing season (bud break till harvest). Canopy, soil, and composite (soil and canopy) surface temperatures were measured using infrared thermometers. The composite vegetation and soil surface energy fluxes were assessed using independent measurements of net radiation, and soil, sensible, and latent heat fluxes made with a flux tower installed in the vineyard. E and T fluxes computed by TSEB using the composite temperature outperformed the fluxes computed using independent measurements of canopy and soil surface temperature. This result is due in large part to the thermal-infrared radiometer measuring canopy temperature viewing primarily sunlit leaves at the top of the vine canopy and consequently not representative of the average canopy temperature. In addition, in order to consider advection of hot dry air from the dry bare soil in the interrow to the canopy the default value of the Priestley-Taylor coefficient, used in TSEB to initially determine T, needs to be modified. Improved estimation of the energy fluxes by accounting for the relatively complex canopy structure of vineyards will be highlighted.