Parameterization of a simplified soil water balance model using actual evapotranspiration measurements to optimize vineyard irrigation scheduling

Accurate estimation of actual crop evapotranspiration (ETc act) is essential for optimizing irrigation strategies. This study addresses the need for precise irrigation scheduling tools to enhance water use efficiency while maintaining high grape yield and quality. RETOAGUA (RA), a decision-support system based on the MOPECO model, was developed to provide farmers and technicians with reliable irrigation recommendations for annual, fruit tree, and vine crops. The objective of this study was to calibrate and validate RA for simulating both crop cycle length and vineyard (Vitis vinifera L., cv. Tempranillo) ETc act under semi-arid climatic conditions in Spain, providing a basis for a proper determination of the irrigation requirements of the crops. Phenological stages were defined using cumulative growing degree days (CGDDs) and 8 years of monitoring data from the Castilla-La Mancha Irrigation Advisory Service (39 phenological crop monitoring). ETc act was assessed under full and deficit irrigation conditions using lysimeter observations and the soil water balance approach in vineyards located in the provinces of Albacete and Valencia, respectively.,The results evidenced consistent CGDDs calibration and strong agreement between estimated ETc act and the lysimeter observations (2007-2009) (RMSE<0.65 mm day⁻¹, NRMSE<19.2%, EF>0.81, d>0.90, R²>0.82). Under deficit irrigation, calibration years (2003 and 2004) demonstrated acceptable to excellent performance (RMSE 0.20–0.55 mm day⁻¹, NRMSE 10.0–25.0%, EF 0.27–0.92, d 0.85–0.98, R² 0.59–0.99), while validation years (2001 and 2002) exhibited higher variability and lower accuracy.,RA showed robust predictive capacity across different climatic conditions with low input requirements, and adaptability to different agro-climatic conditions, supporting its use a practical tool for implementing regulated deficit irrigation (RDI) strategies in water-scarce areas.