Impact of groundwater depth on crop coefficient: An improved evapotranspiration model

Understanding the impact of groundwater depth on actual crop evapotranspiration (ET c act ) is essential for agricultural water management in shallow water table regions. A four-year field experiment (2019–2023) was conducted at the Wudaogou Hydrological Experimental Station to monitor the ET c act of winter wheat under different groundwater depth conditions, while simultaneously recording key meteorological variables, including air temperature, precipitation, wind speed, net radiation, relative humidity, sunshine duration, soil heat flux, and soil temperature. Based on the observed data, we analyzed the influence of groundwater depth on winter wheat ET c act and actual crop coefficients ( K c act ). The results revealed that both ET c act and K c act exhibited a clear exponential relationship with groundwater depth, showing a significant decreasing trend as the depth increased. Building upon this finding, we developed a Groundwater–Meteorology-Based Actual Crop Evapotranspiration Model (GW–M model) that incorporates both groundwater depth and meteorological factors. In the model, these variables affect ET c act by influencing the K c act . The selection of meteorological factors was guided by the top three variables identified through geographical detector analysis. The model effectively reproduced the ET c act process of winter wheat in shallow groundwater areas. Comparative analysis with other evapotranspiration models demonstrated that the proposed model achieved higher accuracy. This study underscores the pivotal role of groundwater depth in regulating ET c act in shallow water table areas. The proposed modeling approach offers a flexible and scalable framework for simulating ET c act under variable groundwater conditions, thereby providing theoretical support for regional-scale agricultural water management. • Four-year field study assessed groundwater depth effects on winter wheat ET c act . • ET c act and K c act decreased exponentially with greater groundwater depth. • A groundwater–meteorology model (GW–M) was developed to estimate actual ET c act . • The GW–M model performed well under shallow groundwater conditions.