Estimating seasonal agricultural irrigation water use in Michigan: Field-level evaluation of the Michigan Water Use Reporter

The Michigan Water Use Reporter (MWUR) model is a simulation designed to estimate water use from irrigated agriculture in the state of Michigan. The model was developed by Moen (1999) but had never been evaluated against actual grower reported irrigation amounts. The evaluation of this model took place with data from the 2002 and 2003 growing season. Twenty-one fields across central and southern lower Michigan were used as study sites. Volumetric soil moisture and seasonal irrigation water depths were recorded from each site and used to test the simulation. Validation of the simulation was conducted in two stages. First, seasonal irrigation water volumes were compared, using descriptive statistics, to simulated season irrigation output. Second, simulated volumetric soil moisture were validated using field measurements from a capacitance probe. A sensitivity analysis of managerial and crop physiological parameters was conducted after validation. Depth per irrigation, irrigation trigger level, planting date, and root growth rate were analyzed. The simulation tended to overestimate both seasonal irrigation water depth and volumetric soil moisture across all crops. The sensitivity analysis found depth per irrigation and trigger level were by far the most sensitive parameters. These tests indicate the model, while demonstrating sound hydrology, does not properly characterize the methods grower use to decide when to irrigate. Better parameterization of these methods will result in a more robust simulation.