Estimating groundwater evapotranspiration from irrigated cropland incorporating root zone soil texture and moisture dynamics

Estimating evapotranspiration from groundwater (ET_g) is of importance to understanding water cycle and agricultural water management. Traditional ET_g estimation was developed for regional steady condition and is difficult to be used for cropland where ET_g changes with crop growth and irrigation schemes. In the present study, a new method estimating daily ET_g during the crop growing season was developed. In this model, the effects of crop growth stage, climate condition, groundwater depth and soil moisture are considered. The method was tested with controlled lysimeter experiments of winter wheat including five controlled water table depths and four soil profiles of different textures. The simulated ET_g is in good agreement with the measured data for four soil profiles and different depths to groundwater table. Coefficient of determination (R²) and coefficient of efficiency (NSE) are mostly larger than 0.85 and 0.70, respectively. This result suggests that the new method incorporating both soil texture and moisture dynamics can be used to estimate average daily groundwater evapotranspiration in cropland and contribute to quantifying the field water cycle.