Planning For Depletion: Optimal Irrigation in the Pinal Ama under Changing Water Sources

Abstract

As a shortage declaration on the Colorado River appears likely in the near future, many farmers in the Pinal Active Management Area face decreases in Central Arizona Project water and the prospect of returning to groundwater for irrigation. Among other differences, these two sources of water have different costs. Here a simple profit maximizing model is used to calculate a cotton farmer’s optimal irrigation level, finding, in some situations, an incentive to increase the amount of water used for irrigation when switching from CAP to groundwater due to lower cost. The profit maximizing model is used with well data to examine the relationship between the amount of water available to irrigators and profit as well as spatial differences within the Active Management Area. The profit maximizing approach is expanded to a two crop model with alfalfa and cotton, which indicates a preference for cotton over alfalfa when the amount of water available for irrigation is limited.