A Thermal-Based Wheat Crop Coefficient Method Using Additive Crop Growth Models

Accurate crop evapotranspiration simulation is vital for reasonable irrigation planning. The two-step method for crop evapotranspiration estimation has been widely used for irrigation water demand management. However, in the two-step method, the crop coefficient ( K c ) is typically taken as a constant in crop growth stages, which may result in a certain error in evapotranspiration estimation. It is of significance to estimate K c accurately for effective water resources management. Based on three-year lysimeter experimental data collected from the Wudaogou Station for Hydrology and Water Resources, this study proposes a thermal-based K c method for actual crop evapotranspiration estimation. The proposed thermal-based K c method uses air temperature and soil heat flux as input variables, which could mainly characterise the thermal effect on crop growth from the atmosphere and soil. Results showed that the proposed method is effective in estimating K c . The estimated K c highly correlates with actual K c values, which are derived from lysimeter observation, with correlation coefficients greater than 0.87. The proposed method could estimate K c daily, which can be used to estimate crop evapotranspiration accurately