Soil Moisture Evapotranspiration (SMET): A Low-Cost Method for Determining Seasonal Crop Water Demand

Evapotranspiration (ET) is an essential component of water balances that can be estimated using different tools, but heterogeneous landscapes and experimental designs limit their applicability. This study aims to develop a cost-effective, simplified method for estimating seasonal crop ET using soil moisture sensors along the root zone profile and reference ET data from local weather stations. The study was conducted at two sites in Utah, USA to develop and validate a new empirical soil-moisture-based evapotranspiration (SMET) model that estimates seasonal ET based on the relationship between reference ET (ET _r ), changes in soil moisture, and actual evapotranspiration (ET _a ). The initial model was constructed using detailed flux measurements from Modena, Utah, where an Eddy Covariance (EC) flux tower was installed. The model was validated with EC tower measurements at one of the research sites in Vernal, Utah showing a Root Mean Square Error (RMSE) and Root Relative Squared Error (RRSE) of 1.26 mm day ^− 1 and 0.65, respectively, which demonstrated high accuracy. This approach offers a practical solution for farmers, water managers, and policymakers to estimate crop water consumption, supporting better water resource management in arid and semi-arid regions.