International Journal of Environment and Climate Change

The present study was conducted to calibrate and validate the FAO AquaCrop model for simulating wheat (cv. PBW-502) productivity under the agro-climatic conditions of Prayagraj, Uttar Pradesh. Field experiments were carried out during two consecutive rabi seasons (2018–2019 and 2019–2020) involving 15 treatment combinations of three sowing windows (D1: 17 November, D2: 2 December, D3: 17 December) and five irrigation schedules based on physiological growth stages (I1 to I5). The model was calibrated using experimental observations from 2018–2019 and independently validated using 2019–2020 data. Model performance was evaluated using Root Mean Square Error (RMSE), Normalised Root Mean Square Error (NRMSE), Coefficient of Determination (R²), and Willmott’s Index of Agreement (d). The AquaCrop model simulated grain yield, biomass, and canopy cover with close agreement. For grain yield, RMSE ranged from 0.03 to 0.19 t ha^-1, NRMSE from 0.86% to 5.52%, and d-index from 0.97 to 0.99 across sowing dates and irrigation schedules. Biomass accumulation showed satisfactory agreement with d-values between 0.86 and 0.98. Canopy cover simulations at 30 and 90 days after sowing (DAS) showed satisfactory agreement (d = 0.90 - 0.98). The model showed satisfactory performance for evaluating irrigation schedules and sowing dates under the tested subtropical conditions; however, the two-season dataset and its limited evaluation under extreme heat stress represent operational limitations. Future work should include multi-location trials and integration with high-resolution climate forecasting models.