A three-source SVAT modeling of evaporation : application to the seasonal dynamics of a grassed vineyard

International audience; A parsimonious and versatile Soil-Vegetation-Atmosphere Transfer (SVAT) model is proposed for three component vineyards, which includes vine foliage, grassed soil and bare soil. A three-source energy balance approach describes the energy and mass transfer between the soil-plant continuum and the lower atmosphere with an hourly time step. It is coupled with a soil water balance module running with a daily time step. The model makes use of standard meteorological data together with parameters describing foliage development, grass and soil characteristics. The model is calibrated by means of the Multi-objective Calibration Iterative Process (MCIP) algorithm and next validated for evaporation and soil moisture over a dataset collected in a Southern France grassed vineyard. The validation exercise is twofold. It focuses first on the daily course of evaporation derived from the surface energy balance module only, forced with meteorological variables, net radiation and soil moisture. The comparison against Eddy Covariance measurements shows a good agreement (R-2 = 0.96 and RMSE = 14.0 W m(-2)). Next, a simulation coupling the surface energy balance module with the soil water balance module is validated over Eddy Covariance and soil moisture measurements. Simulations throughout two contrasting growing seasons provide good estimates of daily evaporation (R-2 = 0.90 and RMSE = 0.43 mm d(-1)) and soil water content (R-2 =0.98 and RMSE = 6.95 mm). Model inaccuracies arise mainly under conditions of strong surface runoff. Results also suggest that the parameterizations relating the surface-atmosphere module with the soil module (i.e. stomatal resistance) should be carefully examined under water stress conditions. Finally, the model versatility is addressed through a set of simulations. It appears that the modeling approach allows assessing the seasonal water balance of vineyards with different structure (grass fraction or distance between rows) and that it could be applied to similar cropping systems.