Water duties: Arizona’s groundwater management approach

Agricultural water duties have historically been used to settle al- Iocational disputes, adjudicate water basins, size canals, and schedule irrigation. The Arizona Department of Water Resources is now using water duties to reduce demand for groundwater in the management areas of the state. This paper reviews the scientific determinants that the water duty comprises and describes the concept’s implementation in Arizona’s active management areas. The water duty is only one of several approaches to groundwater allocation. New Mexico, Oklahoma, and Nebraska employ approaches that differ considerably from Arizona’s. Arizona’s allocation varies per acre, depending upon a farm’s cropping history. In the other three areas, the allocation is uniform per acre and is more dependent upon supply management goals. Differences in spatial and temporal use flexibility also occur between allocation systems. Each of these differences produces efficiency and equity ramifications.