Comparison of Crop Water Use Estimation Methodologies in Irrigated Crops

As increasing drought events limit water resources available for irrigation, farmers and other water users are looking for ways to monitor how much water crops use over a growing season. The amount of water used by crops over time is the evapotranspiration (ET) rate. This study compares different methods for ET estimation to recommend methods to water users based on their accuracy, efficiency, and accessibility. Each method was used to estimate ET for sprinkler-irrigated corn and alfalfa fields in Modena, UT over the 2021 growing season. The Soil Moisture based ET (SMET) method was used to estimate ET based on daily changes in the soil water content. The OpenET web platform [www.openetdata.org] and the OpenET Application Programming Interface (API) were used to retrieve ET estimates based on imagery from the Landsat satellite. ET estimates for the area were also retrieved from a Utah Department of Natural Resources (DNR) report. The eddy covariance (EC) method is accepted as the standard for estimating ET and served as the standard for the comparison of all other methods. Results indicate that while all methods underestimate ET, the SMET method agrees most closely to the EC method. Further analysis of the OpenET and Utah DNR methods is required to fully explain the reasons for the apparent ET estimation discrepancies. This study also highlights the advantages and limitations of each method