Combining a water balance model with evapotranspiration measurements to estimate total available soil water in irrigated and rainfed vineyards

• We present an algorithm designed to calibrate the soil water balance in terms of TAW.
• The model was applied in vineyards under severe water stress and fully irrigated.
• The model was validated versus ET and soil water content measurements.

This research presents an algorithm developed for calibrating the soil water balance model (SWB) in terms of total available water in the soil root zone (TAW) assimilating actual evapotranspiration (ET) data. After calibration, the TAW value is used to estimate the actual ET and water stress processes at canopy scales. This methodology also allows for the estimation of the minimum TAW value that explains the ET rate in the absence of water stress. The model was applied in three vineyards grown under rain-fed, full irrigation and deficit irrigation conditions in La Mancha (southeast Spain) and the Alentejo (southern Portugal). The values of TAW obtained for the analyzed vineyards illustrate the variability of this parameter. TAW values varied from 180 to 390 mm depending on the water availability for growing conditions. The use of these TAW values allowed for a precise estimation of the ET values, water content and water stress process for the validation campaigns. The RMSE values obtained when comparing measured and modelled ET were lower than 0.65 mm/day for each analyzed seasonal campaign. The application of this methodology in operational scenarios will allow for the estimation of TAW for each site in order to optimize the irrigation applied, even in deficit irrigation schemes.